Star Formation, Part I

Sorry we’re late, we just had to take the time to evolve this post.  That’s right, we are here to discuss the first step in a star’s evolution!  In one of my many twisted analogies I said that stars are like people.  So, we have the early stages of a star’s life!  Just like how people have baby and teenage years we have the topic of star formation and nebulae (again, twisted analogies…but I think we can all deal with the puns and any bad humor presented here).

Interstellar medium (ISM) is quite literally “the stuff between the stars”. And by stuff, we mean the gas and dust that stars form out of, and often, spew back into space during their lifetimes through stellar winds or supernovae. Unsurprisingly, hydrogen makes up most of the ISM as HI (neutral), HII (ionized), or H2 (molecular), and helium makes up most of the remainder. It’s hard to detect neutral hydrogen because its single electron is in the ground state, so it cannot jump down an energy level to release radiation, and only rarely does a photon of the right energy come along to boost the electron to a higher energy level. However, astronomers can still detect HI using the 21 cm line. This relies on the fact that electrons and protons both have a quantum “spin”. A hydrogen atom has slightly less energy when they are spinning in opposite directions as compared to when they are spinning in the same direction – the photon corresponding to this difference  in energy has a wavelength of, you guessed it, 21 cm.

While it doesn’t make up a large percentage of the ISM, dust blocks light and also reddens it, since longer wavelengths are less likely to interact with dust grains. It is sometimes found in the form of Polycyclic Aromatic Hydrocarbons (PAHs), which are relatively complicated hydrocarbons with ring structures. Why do we mention PAHs? Not for any important reason, they’re just thought to be necessary for life (even though we consider them scary carcinogens down here on Earth).

Thus, we start our evolution with stuff.  What is this stuff?  Oh, various things.  Hydrogen, helium, lithium… Yes, lithium in fact would exist, but we will ignore this until a bit later into the post.  But we just have stuff, what do we need to make a star?  Well, this stuff, at this point forming a nebula, literally meaning cloud, is not condensed.

The Eagle Nebula

Soar like an Eagle Nebula (yes, nebulae are pretty). Credit: Jeff Hester and Paul Scowen (Arizona State University), and NASA. From http://outreach.atnf.csiro.au/education/senior/astrophysics/stellarevolution_formation.html

Before we go further, we should note that there are several kinds of nebulae. Reflection, emission, absorption/dark, planetary, supernova remnants… heck, people used to call galaxies and star clusters “nebulae” as well. Note that this post will deal with star forming regions or cloud complexes, so there won’t be SNRs or planetary nebulae because they don’t really apply to the start of a star. Emission nebulae are formed when gas molecules are excited (yes, you be excited as well) by radiation from a nearby star and release radiation; they are typically red in color because of their hydrogen content. Reflection nebulae occur when starlight doesn’t have enough energy to excite the electrons and just reflects off dust particles instead (typically blue because shorter wavelength light is easier to scatter). Both these types of nebulae signal regions of star formation. Absorption nebulae, or dark nebulae, appear “dark” because they’re made of relatively dense clouds of dust that simply block light from behind them.  And why study these?  Well…they’re dark for one.  So yeah, they block out light, how annoying!  Luckily we have some ideas of how they block out light, but if we didn’t it would be quite the nuisance.  But then what else could they involve (you know, since astronomy just can’t leave something as is)?   Well, there are these things known as Bok globules.  They are smaller dark nebula that are also regions of star formation in HII regions, and they can also hint at some star formation in general since they can be in molecular clouds.

Horsehead Nebula (a dark nebula)

One of the most famous dark nebulae in the sky. Credit: NASA

B68

Barnard 68-the other most famous blotch of black stuff in the sky that is actually stuff. Credit: NASA and cfa.harvard.edu/COMPLETE

Thackeray’s globule-the other OTHER most famous blotch of black stuff in the sky indicating star formation. Yay for Bok globules! Credit: HST and cfa.harvard.edu/COMPLETE/

But back to stars. For a star to form, a chunk of the gas cloud has to increase in density to such a point that it collapses under its own gravity. Either random turbulence within the gas cloud itself may achieve this critical density, or an outside source, such as collision with another gas cloud or shock waves from a nearby supernova, may be involved. Astronomer James Jeans derived an equation to show the minimum mass necessary for a cloud of a certain radius to collapse; we of course know this as the Jeans mass. However, the Jeans mass neglects external gas pressure (which is factored in by the Bonner-Ebert mass) as well as several other factors that may influence collapse. The initial gas cloud fragments into several pieces, for reasons that we don’t quite understand yet, and these pieces may fragment further until their density is so great that they just keep collapsing.  And you guessed it, this is called fragmentation!  These are important because they can form binary stars and relate clusters of many stars, both of which are quite useful.  Fragmentation itself stops and changes due to differences in density and energy radiated as the collapse occurs.  Aside from this, factors influencing protostars are mainly motions (rotational or angular) and magnetic aside from atoms.

And to further the fascination let’s add some more factors.  As we said there is rotation and magnetic fields.  There are also differences in density.  Another factor?  Well, a commonly seen occurrence is to see stellar winds from massive stars blowing at or ionizing the protostar such that they are eroded away.  So, what do we get from these complications?  Birth lines!  Yes, they really are just like humans, well not at all actually, since these are actually lines for the beginning of protostars’ evolution.

Also, massive stars may not form from large amounts of mass collapsing, but from multiple smaller stars coming together because the high temperature, luminosity, and radiation associated with large stars are thought to be hard to achieve by collapse.  But this may not be needed because mass can fall into an accretion disk (an accumulated disk of material) around the star.  This could then make a massive star grow, and it wouldn’t be fully ionized, which could prevent collapse.

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“A typical interstellar cloud is supported against collapse by internal turbulent motions.”

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“Once such a cloud is “tipped over the edge” and starts to collapse, it reaches a state where gravity can pull the gas together to form dense “cores”. “

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“These cores continue to collapse, often fragmenting further, until they form star – sized clumps.” To show what we have been explaining thus far. Credit for the above three pictures: ircamera.as.arizona.edu and Matthew Bate

So, are we at a star yet?  Nope, we still have a ways to go. You see, like we said stars evolve, like life theoretically, but we can track them much better (see, stars are so much more stellar than other things).  Tracks we say?  Yes, evolutionary tracks in fact!  These curves show major tracks for different mass stars.  The energy produced during this time is created from falling material going so fast that it goes supersonic and has what’s called a shock front, which basically just means that we get this whole mix of really fast moving stuff slowing it down to the point where energy is released.  Another note is that material is accumulating, or accreting (yes, it’s a word that will be used many many times) around the star as it collapses.  In fact, the collapse that occurs appears to be of infrared sources which appear in Bok globules.

Alright, but now what do we have?  Well, we’ll just say by this point we’ve gotten a protostar.  This collapses through the Kelvin-Helmholtz mechanism of gravitational contraction which can release potential energy as heat, explaining the light we see from a protostar.  Moving on we have the oh so important Hayashi Track!  In fact, Hayashi did many things with these early stars, but let’s just start with this.  The Hayashi track shows that for a collapsing protostar the opacity of a star increases from slight ionization of hydrogen.  This results in convection in the envelope, which he managed to show as a vertical line on the H-R diagram.  This line shows that the collapse eventually decreases luminosity and increases temperature.  The best part about this track?  It actually forbids certain types of stars from forming, greatly helping our search for star formation.

Hayashi Track

Credit: David Darling

After all this and some modelling we get what’s called pre-main sequence evolutionary tracks.  These are basically more tracks to see the evolution of stars.  Interestingly, a core and convective zone begins to form at this point, which can allow some slight fusion through the PP chain and the CNO cycle, but not enough to really stop collapse.  This can produce a slight expansion such that luminosity would actually slightly decrease.  In lower mass stars carbon generally can’t be burned, so later in life the CNO cycle wouldn’t really occur as much, but in massive protostars it’s slightly different since the CNO cycle would be more dominant.  So, what does this show?  Basically that mass matters.

We’ll cover types of Pre-Main Sequence objects and more star formation in Part II.

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TL;DR – Stars form out of interstellar medium, massive clouds of gas and dust. A gas cloud becomes denser in one area, which collapses under its own gravity and also fragments to form several protostars. These not-quite-stars follow evolutionary tracks as they evolve towards the main sequence on the H-R diagram.  And what is basically the most important factor?  Mass.  This beginning stage is important to understand where to look for types of stars and events, to understand the processes in stars, and to help make better interpretations of how the universe works.

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Sources:

Nebulae:

Star Formation (these sites cover most of the star formation post in general, which is why this isn’t split up so much)

Carroll and Ostlie, An Introduction to Modern Astrophysics, 2nd edition (pg 398-445)

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Keeping Time in Astronomy

We are sorry this post was so untimely, but you see it was to show how important keeping time is (okay, just bear with us).  Yes, it’s about time for this post!  But why?  That’s because it’s about time of course!  Time is completely derived from watching the motions or being able to see the light of the Sun, Moon, and other objects.  Things can appear slow, fast, or like nothing in terms of time, it’s all relative of course.  In fact to an extent we can say that these clocks have driven us cuckoo!

The basis of time is the SI unit, the second, a special little s that is the only unit that can’t follow our normal SI system of 10.  Where could this even come from?  It used to be one second of minute of one hour of one solar day, therefore being 1/86,400 of a solar day.  Now we can use the wonders of the atomic clock!  The reason is because of all sorts of interference with complex “leap” times; there is even a leap second along with the leap year.  These leap times were done to correct the calendar due to all sorts of errors.  All these factors have led scientists and astronomers to develop many definitions of time.

To start, we have the year.  On average it is about 365.25 days.  So, where does the decimal come from?  To start we have a few different ways to keep time.  Sidereal time, or sidereal motion, looks to the revolution of the Earth with respect to DISTANT STARS.  This comes from observing the sky.  Solar time, also known as synodic motion, is with respect TO THE SUN, it is a daily observation to see when it rotates to get to the same place.  How much of a difference could this make?  Well, the solar day is about 24 hours.  The sidereal day is 23h 56m 4s.  In addition to the slight error, think about how the stars are moving in space.  We are slowing down/speeding up throughout the year, and on the scale of billions of years, or even a few years, these errors can make a fair amount of difference.  To be direct, the motions of the Earth are quite inaccurate.  That alone is reason to develop more accurate time-keeping.  Also, the sidereal year is an orbit around the sun relative to stars, while the tropical year measures between two successive spring equinoxes.  This alone creates a difference of 20 minutes in the year, so  this too builds up over time.

You can see not only is this revolutionary, but it is also timely (from Prof. Richard Pogge, Astronomy 161: An Introduction to Solar System Astronomy, http://www.astronomy.ohio-state.edu/~pogge/Ast161/Unit2/time.html, listed below ).

What would astronomy or science be without have more than a few ways to do something?  There is also standard time.  This was using railroads and telegraphs to standardize time.  It synchronizes clocks of different locations within a time zone not exactly using solar time.  This goes into time zones, dividing the Earth into zones of 15 degrees of longitude.  But this links into Universal Time (UT).  This was used to develop time offsetting from the Prime Meridian.  It was to replace the Greenwich Mean Time (GMT) which had multiple definitions.  UT is technically closer to a Mean Solar Time, with Greenwich as the reference.

But then there is more of course.  Eventually, with all these errors scientists decided that our definitions were a bit faulty.  So, the second was defined again.  The interesting thing about the second is it’s the only unit that isn’t regularly used with multiples of 10.  So, this develops into atomic time.  By using Cesium-133 (this is a specific isotope, but if you get your hands on cesium in general…well, please be responsible/have fun with the explosion) has a specific number of cycles with decay.  This has developed  into the notable atomic clock.

Another type of advanced time keeping is Ephemeris Time (ET), based on observing the motions of the planets and the sun.  ET was briefly used to define the SI second, but it has since been phased out as we have discovered better ways of timekeeping.  Now we’ll return to something nuclear.  Nuclear time involves an H-3 (tritium) isotope that beta decays to He-3.  When tritium reaches its half life a nuclear time elapses.  Next we have something very astronomical: pulsar time, the use of binary pulsars (yes, massive stars rotating around each other) to find periods varying by less than a second because of their relatively definite motion.

Lastly, we have one of the more important astronomy-related methods of keeping time.  These are Julian Dates (JD).  This is a continuous count of days since noon Universal Time on January 1, 4713 BCE (this would be on our everyday Julian calendar).  This may seem quite arbitrary, but the reasoning was that at the time of its development, there were no known historical events before this year, so as to avoid negative dates or BC/BCE/AD.  It also links to solar and lunar cycles.  About 2.5 million days have occurred since then, and it may not seem obvious, but this calculation has to take into account leap years, days, minutes, seconds, and other inaccuracies.  However, it is much more accurate and can better show second differences in data collection.  To make life easier, below we have these formulas:

a=\frac { 14-month }{ 12 } \\ y=year+4800-a\\ m=month+12a-3

For dates in the Gregorian calendar:

\\ JD=day+\frac { 153m+2 }{ 5 } +365y+\frac { y }{ 4 } -\frac { y }{ 100 } +\frac { y }{ 400 } -32045

For dates in the Julian calendar:

\\ JD=day+\frac { 153m+2 }{ 5 } +365y+\frac { y }{ 4 } -32083

Aside from this we should note what a common notation is-J2000.  This is related to epochs, saying that time is starting from the JD on the date January 1, 2000.

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TL;DR

Time can be taken from keeping track of specific stars in the sky, relative to the sun, from atomic clocks and pulsars, or simply by measuring the amount of time from a specific date.  While time may not seem directly important, but a lot of work has been put into this concept.  It is the basis of a large portion of physics and technology.  Astronomy itself benefits immensely from being able to orderly be able to keep track of time for objects.  So next time your clock wakes you up in the morning, remember to not throw it across the room, because it’s just another way of reminding us how important time is.  Also, it means that you should get the heck out of bed or else you’ll be late.

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Sources:

Time in general

http://physics.nist.gov/cuu/Units/second.html 

http://www.astunit.com/astunit_tutorial.php?topic=time

http://www.maa.mhn.de/Scholar/times.html

http://www.maa.clell.de/Scholar/calendar.html

http://www.astronomy.ohio-state.edu/~pogge/Ast161/Unit2/time.html

http://astronomy.nmsu.edu/nicole/teaching/ASTR505/lectures/lecture08/slide08.html

http://curious.astro.cornell.edu/timekeeping.php

http://www.skyandtelescope.com/howto/basics/3304611.htm

http://www.optcorp.com/edu/articleDetailEDU.aspx?aid=2193

Julian Dates

http://aa.usno.navy.mil/data/docs/JulianDate.php

http://scienceworld.wolfram.com/astronomy/JulianDate.html

http://curious.astro.cornell.edu/question.php?number=88

http://www.tondering.dk/claus/cal/julperiod.php#formula

Apparent/Absolute magnitude, Color Index

Before we begin, for those who didn’t see the About page, we’re sorry but we have to limit posts to one per week.  This is because we both have piles of schoolwork to do, but we will try to keep up with one post a week.

This post will involve more about light, as we said it’s quite important.  In fact, this post will discuss how we can use light to predict distances from Earth.  At this point, math should be expected, along with checking units and significant figures.  In fact, we will be introducing one of the most important equations for distance calculations in an Astronomer’s arsenal.

Now we go on the next part of our journey, to Greece of course, where we are joined by the man Hipparchus. He developed a system of apparent magnitudes (denoted as m), which determines how bright stars were by looking at them here on Earth.  For some reason he decided that it would be more logical to say that as the numbers decreased the stars became brighter, resulting in the scale ranging from m=1, the brightest stars, to m=6, the dimmest.  This was mainly because no highly accurate equipment was available, but this is still extremely important as it describes how objects would appear from an observer on Earth.  Originally the system was just based on naked-eye observations, but modern astronomers decided to fix it up.

Now the scale is logarithmic and compares ratios of apparent magnitudes for stars.  Apparent magnitude is now considered to be brightness or flux measured in Watts per square meter.  It was decided on this scale that 100 would correlate to a magnitude difference of m=5.  This should be emphasized as a difference since for the brightness ratio of  B1/B2 should be equal to the magnitude difference of m2-mwith the formula:

B2/B1=100(m1-m2)/5

Taking the log of both sides we get:

m1-m2 = -2.50 log(B1/B2)

With that we can show that when the brightness ratio equals 100 then we take log(100) which equals 2, multiplying by -2.50 to get -5.  But this still works since the scale shows that the object is brighter as the magnitude value decreases.  In addition, that means that if you were to measure between one magnitude it would be a factor of 100.4 which is equal to approximately 2.512 since it comes from 1001/5.  So, a 1st magnitude star would be 2.512 times as bright as a 2nd magnitude star, and 2.512or about 6.310 times as bright as a 3rd magnitude star.  Also, Hipparchus’s scale has had an increased range of magnitudes.  The Sun for example is now m=-26.83.

Next we need to establish how we can show radiant flux, denoted F, or those brightnesses.  Earlier we mentioned it as watts per square meter, which is exactly shown by a familiar manipulation using light and surface area of a sphere.  This is the inverse square law (we can call this brightness or flux, we will now be using F for flux):

F=L/(4πr2)

Now that we have explained how we can view objects with the unaided eye and defined brightness we have to show how to find the actual magnitudes of all objects.  How would this be done, though?  Astronomers decided to create a system of absolute magnitudes, denoted as M or Mv, which shows what the magnitude of stars and objects would be at a set distance of 10 parsecs.  This works since instead of having all sorts of objects with different actual magnitudes and different distances from the Earth an established sphere of points can be used to better show the magnitudes.  With that and the inverse square law in mind we can create a flux ratio to show how much the magnitudes would be from this set distance.  Again, 5 magnitudes separate the apparent magnitudes of two stars which would show a flux ratio of 100.  This is the very same brightness comparison formula we had earlier.  We can actually manipulate that into something called the distance modulus.  We can say that:

100(m-M)/5=F10/F=(d/10 pc)2

This shows that for the flux ratio of a star’s apparent magnitude to its absolute magnitude and for F10, which would show how the star would appear from 10 parsecs, would equal the distance to the star if it were at 10 pc away.  This can therefore have multiple manipulations to show a star’s distance away:

d=10(m-M+5)/5 pc

Or a star’s apparent and absolute magnitudes:

m-M=5log(d/10)=5log(d)-5

If you were wondering how this could be useful if we don’t necessarily know the distance or absolute magnitudes of every star (you could certainly find the apparent magnitude as it is defined by how an observer would see it from Earth), that is a very good question.  Later we will discuss that for certain stars the absolute magnitude is extremely consistent and can be used to find distances very well.

There is still more to this story.  The apparent and absolute magnitudes mentioned are measured as bolometric magnitudes, which detect flux from a star across all wavelengths of light.  It would be nice to do this, but it is generally easier to target specific wavelengths especially since certain objects can be analyzed better in them.  For this we have to look at what we use.  UBV wavelength filters are used to find a star’s apparent magnitude and color.  U is the ultraviolet magnitude with a filter at 365 nm and bandwith of 68 nm, B is blue magnitude with a filter at 440 nm and a bandwith of 98 nm, and V is for the visual magnitude (sometimes considered green) with a filter at 550 nm and a bandwith of 89 nm.  This creates multiple color indices which compare the different wavelength filters to show a star’s apparent or absolute magnitude.  The actual device, the bolometer, uses an association between temperature and color as mentioned in the last post to show them.  The indices are differences between magnitudes of the U, B, and V to equal absolute magnitudes shown as:

U-B = Mu – Mb

and

B-V = Mb – Mv

Since we already noted as the magnitudes increase the brightness decreases we can say that a star with a smaller B-V index would be bluer (as the blue was filtered out more) and would show both that the star is brighter and hotter.  The same would apply for the U-B in that lower values would be more ultraviolet and therefore be brighter and hotter as well.  So, overall the purpose of U-B and B-V is to quantitatively show what the color and temperature of a star is.

With this we can next say that there is the bolometric correlation, or BC, which shows the comparison between bolometric and visual magnitudes (mboland Mbol are really just m and M):

BC = mbol– V = Mbol – Mv

There is another factor influencing these formulas.  It is called interstellar extinction which creates the effect known as interstellar reddening, denoted A as another magnitude.  When it isn’t noted in the question you should ignore this, but it is good to know all the factors influencing this important distance equation.  Interstellar extinction refers to the presence of interstellar dust that absorbs or scatters light from an object.  The effect is stronger at shorter wavelengths, which interact more strongly with dust. Therefore, red light can be seen more,  and if something appears more red than it “should”, then dust is present.  This was proven after comparison between expected and observed emissions showed that there was an inaccuracy.  If a question mentions some amount of reddening the following corrections are made:

The distance modulus becomes d = 10 0.2 (m – M + 5 – AV)

B-V values since the color is changed it becomes

True color = (Bo-Vo), Observed color is (B-V)

(B-V)=(B+Ab) – (V+Av)

(B-V)=(Bo-Vo) + (Ab – Av) = Intrinsic color + color excess

Since extinction will occur more in the lower wavelengths, this increases the V values relative to the B or U values.  A test can also ask about how this can show in ratios, where it would show Ab/Av or Au/Av.  In this case you would have to be given the value of the Av, and then multiplying the two ratios by the Av would get Ab and Au, such that you can correct either your B-V or U-B values.

The last thing to note is the color-color diagram.  This relates U-B and B-V indices for stars, and it can show temperature and color as well.  Stars actually aren’t perfect blackbodies, so even if they get close the diagram won’t form a straight line.  Here is an example, but know that a color-color diagram can be applied to objects with many stars, which will look different:

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TL;DR: Developing methods of organizing stars and understanding distances is important in Astronomy since this allows Astronomers to better understand our place in the universe and to construct formulas which explain it well quantitatively.  Apparent magnitude is how bright something appears to be, while absolute magnitude shows how bright something actually is from a set distance of 10 pc.  With this the distance modulus can be derived to find the distance to most objects.  Color indices also are studied to show the temperature, color, and characterize stars better.  Lastly, a correction must be made for interstellar dust.

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Sources and further reading:

Spectra

Spectra (plural of spectrum) were mentioned throughout this blog, and they will be mentioned many more times.  It is the best kind of spectrum, the electromagnetic.  They can be used to study stars, DSOs, and even the planets and moons!  Since stars can emit all sorts of light they are also split into classes based on their spectra.  Let’s get right into this extremely useful tool, but be warned that there will be some math.

Atoms have quite the history and must be understood to understand those lovely spectra since all atoms produce different spectra.  The atom below is the Bohr model, named after Niels Bohr, of a Hydrogen atom.  Also, the electron paths are called orbitals or shells.

Simply this (astronomyonline.org physics concepts-the atom).

There are essentially seven energy levels, numbered one to seven, represented as n=# (n is known as a quantum number) and referring to the orbitals, such that one is the closest to the nucleus and seven is the furthest.  A relationship exists showing that as an electron gets further from the nucleus it gains energy, usually coming from a photon or from heat.  When an atom is in the ground state all of its electrons are in the lowest possible energy level, while when it is in an excited state at least one electron is in a higher energy level from the lowest possible.  This is known as jumping energy levels, but please don’t think that this involves a child that drinks caffeine and gets all energetic and jumpy.  (In fact, it is probably recommended to not give children caffeine but that’s another story.)  Moving on, ionization can be more specifically defined as when the amount of energy the electron absorbs is greater than the allowed energy of all orbits.  Atoms want to be fairly stable, unlike jumpy little kids, which is why all sorts of things form, from salt to water.  So, an atom that is excited ultimately will have the electrons jump back down to the ground state.  But to have gone to a higher energy level the electron had to gain energy, meaning that for it to drop to a lower energy level, it has to emit energy.  That is where spectra come from.

Basically this. Sadly if the atoms produce gamma rays it won’t turn people into the Hulk. In fact, if atoms produce gamma rays it is recommended to go far far away and to hide (astronomyonline.org physics concepts-the atom).

Spectral lines can be produced at specific wavelengths from atoms.  Electrons that absorb energy must either absorb all or none of it since this energy comes in packets called photons.  Therefore, it is true that each and every single atom that has a different structure MUST absorb and emit different amounts of energy.  In essence, this process starts with absorption of energy and ends with emission of energy.  Atoms have certain lines which show optimally in certain temperature ranges, so this is yet another hint they can show about stars.  Spectra can be split into three types: continuous spectrum, emission lines, and absorption lines.

A continuous spectrum is basically a rainbow, all colors of light.  This is the prime, beautiful example of a spectrum that anyone has seen in nature.  We noted in the history section that it took many people to explain the effects seen in the continuous spectrum as it is normally seen and the dark lines seen by Fraunhofer. Notably Kirchoff did this, and the rules are:

1. A luminous solid or liquid emits a continuous spectrum of all wavelengths.  It has no lines in it.

2. A rarefied luminous gas emits light whose spectrum shows bright lines.  These lines are called emission lines.

3. If the light from a luminous source passes through a gas, the gas may extract certain specific energies from the continuous spectrum.  We then see dark lines where the energy has been removed.  These dark lines are called absorption lines.

Three types of spectra

Very colorful (NASA spectra introduction from Imagine the universe)!

To explain its usefulness in stars, certain elements will show prominently in the spectral lines since stars are insanely hot.  In general, certain objects show more emission lines or absorption lines depending on their composition, and every single aspect to spectral lines can be studied to learn immense amounts of information about stars.  They are made of plasma, but since that is ionized gas the 2nd and 3rd rules apply.

Since Hydrogen is the most abundant element in the universe, a variety of people developed series to explain its various spectral lines.  It was understood that series existed to show different energy wavelengths produced as emission lines by Hydrogen.  The major series consist of the Paschen series in the infrared, the Balmer series in the visible, and the Lyman series in the ultraviolet.  For the Lyman series the shortest transition seen is called Lyman-alpha (n=2 to n=1) at the 122 nm line.  For the 103 nm line (n=3 to n=1) it is called Lyman-beta.  For the Balmer series the 656 nm line is Balmer-alpha or more commonly H-alpha (Hα).  After this the 486 nm line (n=4 to n=2) is H-beta.  Hopefully a trend is shown that the highest nm line transition is named alpha, and then after it goes beta, gamma, etc.

It is from Wikipedia, but do use other sources with Wikipedia when doing research.

Just to make this colorful, we will also show what the Balmer series would look like to us, but it wouldn’t be fun to just have Hydrogen.  Let’s show all the elements!

The wavelengths are measured in Angstrom which is 10^-10 meters, but besides that it’s colorful (ucolick.org under spectra lab)!

From here we must depart to the land of math as the mathematical definition can better show our knowledge of spectra.  If a letter is used once it will not be repeated unless to make a note about it or to change units, so if it isn’t mentioned look to one of the last equations mentioned.  Remember UNITS MUST ALWAYS MATCH.

Going from the Hydrogen series there is a formula known as the Rydberg formula.  It was discovered around the same time the Balmer series was first discovered.  It is highly important because it can be used to calculate the wavelength for energy transitions from emission spectra of Hydrogen, the most abundant element in the universe.  We will show how the formula works.

First, it is important to know the two major equations relating to light.  One is λν = c.  Where:

  • Lambda or λ is wavelength in meters
  • ν or nu (pronounced “new”) is frequency in wave crests or cycles per second
  • c is the speed of light in a vacuum or 2.998 x 10^8 m/s

The other equation is the de Broglie equation E=hν.  Where:

  • E is energy in joules
  • h is Planck’s constant as 6.626 x 10^-34 Joule*seconds.

Using the above equation and substituting for frequency it can be represented as E=c*h/λ.  Both the speed of light and Planck’s constant can be found to have more significant figures, but

For calculating the energy change of an electron:

\begin{displaymath}<br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br />
{\mit\Delta} E = E_0\left(\frac{1}{n_f^{\,2}}-\frac{1}{n_i^{\,2}}\right).<br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br />
\end{displaymath}

Where:

  • $n_i$ is the initial quantum number
  • $n_f$ is the final quantum number
  •  Eo is the initial energy or the energy of the groundstate

For the energy change of the electron if it is negative then the electron should emit a photon of frequency$\nu=- {\mit\Delta}E/h$.  If the energy is positive then the electron should absorb a photon of frequency $\nu={\mit\Delta}E/h$.  This is exactly what leads into the Rydberg formula.  Since $\lambda^{-1}=\nu/c$, the Rydberg formula when substituting is:

\begin{displaymath}<br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br />
\frac{1}{\lambda} = R\left(\frac{1}{n_f^{\,2}}-\frac{1}{n_i^{\,2}}\right),<br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br />
\end{displaymath}

Where:

    Lambda is in nanometers

   $n_i$ and $n_f$ are the same, but it is assumed in the Rydberg formula that $n_f<n_i$ since it is used for emission lines of Hydrogen.  This gives the definition that the Lyman series is a transition to the ground state ($n_f=1$) releasing UV light, the Balmer series is a transition to the first excited state ($n_f=2$) releasing visible light, and the Paschen series is a transition to the second excited state ($n_f=3$) releasing infrared light.

    And the Rydberg constant R:

With this now even you can relate energy, wavelength, and frequency all from spectra.  In fact, combined with the Doppler effect these equations can be used to analyze and see the composition, temperature, or presence of certain objects.

To finish, some jokes that hopefully will be amusing after we have shed light on yet another subject:

An electron sitting in a prison asked a second electron cellmate,”What are you in for?”

To which the latter replied, “For attempting a forbidden transition.”

Q: Why does hamburger have lower energy than steak?

A: Because it’s in the ground state.

Q: What happens when electrons lose their energy?

A: They get Bohr’d.

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TL;DR: Spectra are up there with one of the best tools to use to analyze objects in Astronomy.  Atoms can absorb specific wavelengths of light or emit specific wavelengths of light depending on their size and structure.  This produces spectral lines which appear on a spectrum of light, and this will be different for all atoms of different structure.  Since most of the objects being studied are made of atoms, we find that they produce spectral lines. Hydrogen has been studied extensively because it makes up so much of the universe, and the Rydberg formula helps us calculate hydrogen’s spectral lines.

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Sources and further reading:

 

What are stars?

A good question.  Are they like people?  They live.  They die.  They have populations and clusters.  Technically as Carl Sagan said “we are star-stuff.”  So people and stars are sort of similar.  But the main difference is that they are gigantic spheres of extremely hot plasma.  Okay, so not exactly the same thing, but they are still assuredly awesome.  One could even say stellar.

A star is a large amount of gas, mostly Hydrogen, and is held together by two forces that are essentially equal.  This is called hydrostatic equilibrium.  The name comes from fluid dynamics, where the only fluid, incorrectly, was thought to be water.  The first force is gravity.  On a large scale gravity has more importance and attracts this massive amount of gas together.  But with only gravity attracting the gas inwards there has to be an outwards force to create equilibrium.  This force comes from fusion.  We say fusion powers the Sun because it releases insane amounts of energy and can create a radiation pressure that works outward against the force of gravity.  It has so much energy, it ionizes the gas and is the reason why stars are made of plasma.  The Sun and in fact the whole night sky is all thanks to fusion.

Stars have many qualities which will be discussed later, but an important aspect is that just like anything else they have a structure.  Here is the Sun:

Parts of a Star

If it could talk, it would probably be bragging how hot it is (even though it’s not that hot for a star) and that it is like an onion; it has many layers.

Stars have many shells or layers.  Fusion begins with fusing Hydrogen into a shell of Helium.  In general, as fusion occurs, heavier nuclei sink towards the core or center and form these shells from convection.  The core therefore has the most energy since it takes more energy for higher level reactions to occur and it is the central area of energy production.  But going to the outside of the star it begins to cool down.  This occurs at first through radiation, the transfer of energy by light.  The light travels quickly through a Radiative zone where the light is emitted or scattered.  Then the star transfers energy with its chief method of energy transfer, convection, the transfer of energy through a fluid to balance temperature.  This occurs in the plasma of the star in the Convection zone.  On the Sun, hot fluid rises and moves out of the star, while cold fluid sinks, which is why it balances in temperature and cools down going towards the outside of the star.  Note that energy leaves a star by radiation, not convection, since energy from a star leaves with emitted light travelling through space, and space is not a fluid or solid.

The photosphere is similar to the radiative zone, but it more specifically refers to the presence of light and energy created. It represents the area where the light makes a star become opaque.  The chromosphere is similar to the convection zone and is where the colors of the Sun are mostly seen.  It technically can’t be seen except during a solar eclipse or with a light filter since the light of the photosphere over powers it.  The chromosphere also contains spicules, spikes of gas that eject out to the next part of the Sun, the corona.  This is similar to the Sun’s atmosphere and is made of plasma too.  A mystery still keeping scientists up at night is that the corona is hotter than the surface of the Sun.  But it isn’t just a little hotter.  To compare temperatures, the core is about 15-16 million K, the photosphere, closer to the surface, is about 5700 K, the chromosphere can be 5000-4400 K, and the corona is a million K.  Iron detected in the atmosphere could be the cause, but scientists are unsure.

The Sun also has a magnetic field just like the Earth.  We know it has one due to something known as the Zeeman Effect.  Atoms can produce light associated with magnetism when excited or ionized.  When this light is released lines of light at certain wavelengths can be seen, and these lines can be seen to split due to magnetism.  The magnetic field is most likely due to the movement of plasma which creates an effect similar to a dynamo, which uses motion to rotate a coiled magnet and through some awesome science this creates electricity.  On the Sun it’s a bit different, but theoretically the plasma convecting should be conductive and extremely magnetic, therefore the massive amount of rotation on the Sun  should create a magnetic field.

Many things that occur on the Sun involve this magnetic field, the following are examples.  Sunspots are relatively cool (emphasis on “relatively” since they can be 3000-4500 K) and appear dark.  The magnetic field shifts around a lot since there is so much plasma moving around.  This creates differential rotation (parts rotating differently) in the Sun.  It can get so twisted up it can become like a rubber band, curling up and piercing the outside of the Sun.  This creates a spot where the magnetic field leaves and reenters the Sun.  There is an 11 year sunspot cycle because the magnetic field of the Sun flips like the Earth’s (just a lot more often since it is humongous) and can be traced to have minima and maxima.  Solar winds are streams of charged particles shot out of the Sun which can use the energy of the corona to escape the Sun’s gravity.  These can be the cause of geomagnetic storms, which can affect satellites and technology on Earth or be a possible danger for astronauts.  Coronal Mass Ejections or CMEs are an explosion where all that coiled up magnetic force throws out material into the Corona.   Solar flares are sudden, intense variations in brightness in the Sun.  This results in massive CMEs.  Both CMEs and solar flares are caused by sunspots and are associated with solar winds, but whether CMEs and solar flares are associated is still being researched.  Some of these can be characterized as a solar prominence.  No, not how the Sun is so awesome it is important, famous, or noticeable (though, that should be an alternate definition as the Sun does do that), it is something which can cause a loop-like shape starting in the photosphere and entering out into the corona.

If the Sun could talk here it may say how loopy it is.

There are multiple measurements for stars using the Sun.  They are useful since the Sun is a fairly average star, and it acts as a good basis for comparison.  There is the Solar mass (about 2X10^30 kilograms, fitting the mass of the Earth about 30,000 times), Solar luminosity (about 4X10^26 W, an average lightbulb is 100 W…it’s fairly obvious that the Sun is brighter), Solar radius (sadly not an easy 1 million km, but it is about 700,000 km; able to fit the Earth about 110 times), and age of the Sun (currently about 4.5-5 billion years, which is really long…there is really no other way to put it)

Next is the naming of stars.  Sadly, if you are looking to “buy a star” and name it (perhaps for romantic reasons) you will be disappointed.  At least, if you expect it to mean anything.  Most stars have been cataloged and therefore buying a name for it is the same thing as pointing to a star and making up a name for it, except you’d have to pay for it.  Ancient Astronomers would generally name stars for a relationship to a constellation to make them easier to remember, but now there are catalogs and designations based on the imaging used, coordinates, and properties of the object being studied.  There is the Bayer designation, naming a star based on the constellation and brightness related to a Greek letter (so, the brightest star in the constellation Taurus would be called Alpha Tauri, but ancient Astronomers would call it Aldebaran which is sometimes used as a common name).  But now there are modern catalogs, the major ones being the Messier (as mentioned, M), New General Catalog (NGC), and Index Catalog (IC).  There are many more catalogs, but in general cataloging stars is extremely important.  They allow Astronomers to know where they are looking, what they are looking at, and how to revisit or calculate positions of an object that is being looked for.

One of the most interesting things to all this: these processes and more occur in stars in the whole universe.  As Carl Sagan said, “Billions upon billions”, referring to how the universe has billions and billions of galaxies, each having billions and billions of stars, all functioning more or less the same way.  In fact, the same processes that occur with light bulbs and power plants on Earth occur on the magnificent scale of the Universe, and that is nothing short of mind-blowing.

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TL;DR — Stars are amazing.  They act as prime examples of how mechanics demonstrated on Earth can be applied on extremely large scales.  Stars develop from large clouds of Hydrogen which condense from gravity, and radiation from fusion repels this to maintain a star.  This makes magnetic fields and pretty much a giant ball of plasma.  Stars have been studied for 1000’s of years, and still have many mysteries to be found, which reveal more about the Universe as we study them.

1900’s-Today: Continued

And now we bring you the second part of our history of the 1900s.

Objects or expanding our knowledge of the Universe, who discovered them:

With all these new discoveries, theories, and fancy technologies we must have found more about the Universe, and we did. One object would be the pulsar, discovered by Jocelyn Bell Burnell and Anthony Hewish.  Burnell wasn’t given direct credit until later despite being the actual discoverer.  But either way, the discovery came around 1968.  It was even thought to be some sort of alien, being called Little Green Men (LGM), but after looking at the radio data, they found what we now call a pulsar, appropriate since they spin so quickly that they appears to pulse in milliseconds.  There is also the quasar, discovered by Allan Rex Sandage and Thomas Matthews.  Technically it wasn’t discovered by one or two people, but only found after many people spent many years from the 1940’s to 1962 looking at many many spectral and radio sources.  Both objects show how radio astronomy allowed us to gain a greater insight into the different objects of our universe.

One of the most famous objects to be detected is the black hole.  Technically a black hole can’t be directly seen since it would theoretically appear black as surrounding space, but possible systems and waves of energy created by gravity should be able to detected.  The first person to apply modern physics to one of these very dark objects was Karl Schwarzschild, who found that the mass of the progenitor star (the star that the black hole came from) is linked to the distance that a black hole’s gravity would have an effect.  The black hole actually has some significant betting and arguing behind it.  As stated, Chandrasekhar made a mass limit that was fairly controversial, but with work, people found that a neutron star would have a separate limit which would create a black hole if exceeded.  Stephen Hawking bet that the first strong candidate for a black hole, the X-ray binary system Cygnus X-1 which was found by Thomas BoltonLouise Webster, and Paul Murdin in 1972, would not be one. Hawking is known for making other bets and failing, like betting with John Preskill against Kip Thorne that radiation from a black hole would create an apparent loss of information (he eventually gave up on this), and also betting against the Higgs boson.  But the man did discover Hawking radiation and did very important theoretical work despite suffering from an impairing motor neuron disease.

You can clearly see here that you cannot see this.

Another very famous discovery was that not only was the Universe expanding like Hubble thought, but it is accelerating as a result of dark energy, something that we don’t exactly understand.  This discovery was made in 1998 by  Saul Perlmutter, Brian Schmidt, and Adam Riess, using data on Type Ia supernovae collected by Schmidt and Nicholas Suntzeff.  The name took a cue from dark matter, as both are placeholders to show their very interesting effects for which we can’t quite find something specific that would create the effect.

There is so much going on with the universe as a whole that we have yet to state the full structure of our very own Solar System.  To start we have Planet X, or Pluto (now a dwarf planet).  The man who discovered this officially is Percival Lowell, more of an 1800’s man, but he started the lookout for it in 1906, so we figure he belongs here.  However, Clyde Tombaugh was the one who really found it, in 1930. Funny how with that we have effectively reached the edge of our Solar System.  Well, not really, since  Gerard Kuiper discovered the Kuiper belt, a ring of rocky objects around our solar system, and Jan Oort discovered the Oort Cloud, a giant cloud around the Kuiper belt that is almost a sphere of comet-like objects.  Oort also created some of the earliest evidence of dark matter and improved radio astronomy.  Now, does this mean that we have finally learned everything to know about the Solar System?  No, that would be no fun.

The whole Solar System, very different from the system thought up by Ptolemy. Thankfully no 80+ epicycles.

Besides all this, two other interesting objects were discovered.  One is the brown dwarf; discovered in 1988 by Eric Becklin and Ben Zuckerman.  These are “stars”, put in quotes because they haven’t had the mass to start fusion.  The other major objects we have discovered are exoplanets, officially discovered also in 1988 by Bruce CampellG. A. H. Walker, and Stephenson Yang.  The reason we mention these two at the same time is because they were thought to be the same thing.  Research until 1990 was done to further prove the difference between brown dwarfs and exoplanets, but science always needs further confirmation, so it took until 2003 with some new fancy technology to make it pretty official.  But now where does that lead us?  You see, there is this situation with Pluto.  Finding all these different lower mass objects outside our solar system, we found planets orbiting close to the Sun that are as massive as Jupiter, along with many others.  That, it being different from other planets in size and orbit, and the discovery of another dwarf planet named Eris which is more massive and about the size of Pluto created the debate.  Poor lonely Pluto, but it’s scientific progress.

There is also the idea of popular science.  This was around for a long time, but with the advent of television, movies, and improved speed of print, science could be delivered to a far broader audience.  With magazines there were Popular Science and New Scientist.  With literature there were the big three, Isaac Asimov, Arthur Clarke, and Robert Heinlein.  With television there were Carl Sagan and Bill Nye.  All of this was readily available to people, both as inspiration and for learning.  A last well-known scientist would be Neil deGrasse Tyson, for supporting NASA and taking after Carl Sagan’s Cosmos to teach many about the grand Universe we live in.

As we said, Astronomers (and looking to the name of this blog, Neil deGrasse Tyson specifically) are quotable: “I think of space not as the final frontier but as the next frontier. Not as something to be conquered but to be explored.”

Organizations and general new technologies:

A variety of organizations were formed for space research and to teach the public about Astronomy.  One was the American Association of Variable Star Observers (AAVSO) formed in 1911 for amateur and professionals alike to come together and search the skies.  There was the International Astronomical Union (IAU)  started in 1919.  Yes, the people responsible for Pluto’s demotion, but a unified international organization to meet on issues like these is certainly important.  Next there is the National Aeronautics and Space Administration (NASA), which was founded in 1958, after the US decided that a Space Race was on with the Soviets.  This was some race, even getting men to the moon.  But even with that, “NASA spin-off technologies”, such as kevlar, water purification, and LEDs, stemmed from the research.  Another organization was Search for Extraterrestrial Intelligence (SETI), set up since 1984.  This organization searches everywhere for signs of life, using the Drake Equation, developed by Frank Drake, to show what possibilities to look at when searching for life.

Man on the Moon

An example of how NASA did something very awesome.

There were many technological advancements like the Mount Wilson Observatory.  By the very same man who built the Yerkes Observatory, George Ellery Hale, this was built with the Hooker and Hale telescopes.  The importance to this was that from 1917 to 1948 it was the largest reflecting telescope in the world.  In addition to that, it was built in mountains near Pasadena, which had improved visibility because of smog trapped over Los Angeles.  It was most famously used by Russell for star classification and by Hubble for his major calculations.

But after 1948?  Telescopes could be built bigger, created for specific purposes, and the creation of satellites created a completely new view of space. To start, radio astronomy was mainly ground-based, because sending equipment to space is very difficult, costly, time-consuming, and dangerous if repairs are needed.  So, if fine radio images can be taken here on Earth, they will be.  An example of this is the Very Large Array or VLA, which has detected objects from galaxies to quasars to pulsars.  There was also High precision parallax collecting satellite or Hipparcos.  Launched from 1989 to 1993 by the European Space Agency, this has taken measurements for the parallax of just about 100,000 stars.  The next space telescope launched in 1990 was the famous Hubble Space Telescope.  It has shown parts of space unknown to us with the most detail ever seen.  It actually had an imperfection with the mirror, which was eventually repaired, but that’s why we like our radio telescopes here on the ground.  Speaking of that telescopes on the ground, there are still many that are made for use on Earth.  An example would be the Very Large Telescope or VLT.  It is indeed large,  four reflecting telescopes each with a mirror 8.2 meters in diameter.  It was set up in 1999 in the Atacama Desert of Chile since that would allow for far better observations than near a city with pollution (both light and air).  To show how useful it was, it was the reason scientists can show stars around the supermassive black hole at the center of the Milky Way and revealing the first exoplanet to be discovered.

Another major space telescope was the Chandra X-ray Observatory, searching the skies as of 1999.  This marvel launched by NASA has searched the skies in the X-ray range to show a variety of objects, such as a pulsar in the Crab Nebula.  Yet another major space telescope was the Spitzer Space Telescope, launched by NASA in 2003.  It has imaged a variety of objects in the infrared range.  The next space observatory to be launched was Kepler.  As we said, Kepler had a satellite named after him for being awesome, and his namesake has been searching the skies for exoplanets since 2009, finding over 2,000 candidates, with about 200 being similar to Earth.  Another notable space telescope which hasn’t been launched yet is the James Webb Space Telescope, being launched by NASA in 2018 as Hubble’s successor.  For comparison, Hubble had a 2.4 meter mirror and Spitzer an 85 cm mirror, while the James Webb will have an 8 mirror meter optimized for infrared observations, so it should be able to show a whole new perspective of space.

See Explanation.  Clicking on the picture will download the highest resolution version available.

M1. See, the Messier catalog is helpful, and so are space telescopes at giving us a whole new perspective of it. From: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP) at NASA’s astronomy picture of the day (apod)

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TL;DR — This was quite a bit of history to discuss.  But it is Astronomy, so there is certainly more.  This was to give an overview of the vocabulary, people, and Astronomy in general.  Now we can explore even deeper into the Universe and how it works.  But what is expected in Astronomy and what are the problems after looking at all these people?  It is:

1. Astronomy is really awesome, it can relate to anyone’s imagination.  It is so abstract and great to write, talk, or think about since it is discusses the skies and stars, we can’t reach it yet, but it shows how most subjects can be tied together.  It can even be useful with a variety of satellite or material technologies developed.

2. Astronomers do the work, it’s not often that a eureka moment occurs as much as data, predictions, and models are created to show a probable event either before or after collecting data for it.  It may not sound as exciting, but it actually is more amazing to be able to do that if you think about it.

3. Dark matter, dark energy, quasars, black holes, and many objects even within our own solar system still are not completely understood.

4. Lots Of Acronyms. Or LOA.

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For more on this go to: http://heasarc.gsfc.nasa.gov/docs/heasarc/headates/1900.html

http://www.starteachastronomy.com/astronomers.html

http://www.solarviews.com/eng/people.htm

http://spider.seds.org/spider/ScholarX/hist_mod.html

1900’s-Today: Modern Astronomy, the people, the problems

Now that we have been moving so fast across time, perhaps things will appear to start going slower (hopefully explained in a future relativity post).  The 1900’s has created a lot of mind-blowing problems to discuss in our interpretation of the Universe.  We’ll get into the whole shabang from the Big Bang to now, but the amount of information to cover from the 1900’s to now cannot really be covered in one post, since such a massive amount did happen.  Luckily, not enough to ignite fusion.  So we split the 1900’s, perhaps by fission, into three parts.

General discoveries of principles:

Sir James Jeans and Lord Rayleigh developed the Rayleigh-Jeans Law, of course.  Rayleigh in 1900 and Jeans in 1905 attempted to predict the relationship between wavelength and temperature for blackbodies.  This worked with high wavelengths, but failed catastrophically when it got to lower wavelengths because it showed something called the “Ultraviolet catastrophe.”  No, this doesn’t mean Ultraviolet rays were predicted to cause some major problem for humans, but it did show that by Ultraviolet or lower wavelengths the energy should be infinite.  With that logic, rays from the Sun or any star should have infinite energy, which is untrue, because then there would be infinite energy in the Universe and spectroscopic data would show infinite temperatures for stars.  Oh, also the Earth or any planet wouldn’t be habitable.  Most of these statements contradict the data we have (and the fact that we are still alive).  Still, another step for science.

To continue from the work of Balmer and all the other people who developed spectroscopy there are two other notables.  They are Theodore Lyman and Friedrich Paschen.  They both found spectral lines for the emission spectrum of Hydrogen at different wavelengths.  Lyman found it in UV wavelengths.  Paschen, presumably a passionate man, found the lines in the infrared wavelength.  Hot stuff!  

To continue from Pickering and his “computers” there are three other extremely important women in Astronomy to discuss.  The first is Antonia Maury, who created an early catalog of stellar spectra to help classify them.  Unfortunately, her explanation of the different spectral line widths wasn’t liked by Pickering, so she took a leave for almost 10 years.  She did come back and analyze the spectral lines of the binary star Beta Lyrae,  but she may deserve more credit than it sounds since Ejnar Hertzsprung found value in her work for identifying giant and dwarf stars.  Henrietta Swan Leavitt cataloged over 2,000 Cepheid variables, half of the known amount during the time.  She also developed the period-luminosity relationship, which was used by Hubble and many others as a method of calculating how far a Cepheid was by comparing its apparent magnitude to the absolute magnitude corresponding to its period.  That is up there with one of the most important discoveries in Astronomy and distance calculation.  Lastly, there is Annie Jump Cannon.  She improved upon the theory of stellar spectra.  She created the mnemonic “Oh Be A Fine Girl, Kiss Me”, showing the stellar classes O, B, A, F, G, K, M.  Again, still used and very important.  Sadly, the three women weren’t given all the credit they deserved at the time, and the same went for pay.

“Computers” possibly as important as the computers we use to make this post or to read it with

No Astronomy history discussion is complete without Edwin Hubble.  They say he could have either been an amazing boxer or basketball player, but instead he went into Astronomy.  This is why we make the tough decisions in life.  At the time the latest technology was photographic plates, which had to be examined manually.  But using them he found many Cepheid variables, and he proved they were outside our galaxy using distance calculations courtesy of Leavitt.  He also classified a variety of galaxies, and he found that they were different in distance, shape, and brightness.  This is called the Hubble tuning fork since it looks like a tuning fork, and it doesn’t just sound good, it works well enough to still be used.  The most famous of his discoveries is calculating Hubble’s Law in 1929 by looking at the redshift of other galaxies and calculating how fast away things are moving relative to us.  Using this he was able to create an estimate for the age of the universe, and he showed it was expanding.  Besides being famous, he also gets a very nice telescope which showed us such detailed photos that they can almost let us look back in time by looking into the far edge of the universe (our background happens to be part of the Hubble Ultra Deep Field).

Ejnar Hertzsprung and Henry Norris Russell are known mostly for developing the Hertzsprung-Russell or H-R Diagram.  This will certainly be discussed in another post since besides showing Astronomers’ love of relationships (they are quite romantic), it visually links luminosity, mass, radius, spectral type, stellar evolution, and most qualities we can tell about a star.  Hertzsprung used Leavitt’s work on Cepheids and checked it with parallax to calibrate the relationship.  With work put into stellar classes, he found stars had different qualities and stellar evolution could be linked.  He also used Maury’s work to show color-magnitude diagrams that link width in stellar spectra to density and size.  Russell’s major contribution is the stellar evolution part. With Heinrich Vogt, he showed that mass and chemical composition, but essentially mass, determine the evolution of a star.  In general, Russell introduced much of atomic physics to Astronomy which helped develop astrophysics.

Arthur Eddington is known for many things.  To start he theorized the interior of stars and in 1914 explained how Cepheid variables pulsate.  He also found the Eddington Luminosity,  showing the luminosity of a star while it is in hydrostatic equilibrium, which is when the radiation pressure outwards matches gravitational attraction of mass inwards.  This means he would of course by 1924 explain the mass-luminosity relationship showing that mass and luminosity produced by a star are related.  Eddington also used a Solar eclipse to prove that light is bent from the Sun, major evidence of relativity.  He may have need some of his derivations corrected and tried mistakenly correcting others sometimes, but within 10 years he made three extremely important discoveries to Astronomy.  We do try to explain things well in this blog, but to quote Eddington himself, “Not only is the universe stranger than we imagine, it is stranger than we can imagine.”

Yes, light bends. Also, relativity confuses you and us. Either way, the Solar eclipse is cool.

When we mentioned that Eddington incorrectly argued against other people, mainly we are talking about Subrahmanyan Chandrasekhar.  He is mostly known for the Chandrasekhar limit (1.44 solar masses), which explains the mass limit for white dwarfs.  It also explains how type Ia supernovae are created.  So this discovery was of course criticized by Eddington, who didn’t believe pure mathematical derivation could describe something as massive as a star, especially when it involved quantum mechanics which were not completely understood.  But Chandrasekhar was right in the end, and he even has the Chandra X-Ray Observatory named after him.

Next we shall tune in to Karl Guthe Jansky, the main person to develop radio Astronomy.  By detecting radio waves from the Milky Way Galaxy he showed that a giant dish could be used to detect a variety of objects.  Radio Astronomy has revealed many astronomical objects, since energy can be radiated in all different parts of the electromagnetic spectrum.  It can also be used to detect and calibrate distances, so it is a truly top-notch, or should we say large wavelength, discovery.  Bell Labs should also be noted since not only did Jansky make his discovery there, but much of modern technology was developed there.  He gets all sorts of radio Astronomy-related things named after him, from a unit to a prize.

Jansky’s method of radio Astronomy, not a fancy dish, but it does the job

It may be as confusing as relativity at times, but it has to be mentioned (in fact, it even conflicts with general relativity, which shows how the universe is just confusing).  Everything in science must be approached, so we shall look at the development of Quantum mechanics.  Some main people would be Max Planck, Albert Einstein, Erwin Schrodinger, J. Robert Oppenheimer, Richard Feynman and Werner Heisenberg, in no particular order.  Quantum mechanics shows how particles interact, how light seems to be both a wave and a particle, how classical explanations of physics don’t work on a quantum scale, how position and momentum cannot be both determined at the same time, and pretty much showing how we can always screw with physics just a bit more.  Of course, it isn’t all about cats, so how does this relate to Astronomy?  For one it solved problems like how Wien’s Law and the Rayleigh-Jeans Laws didn’t work, because Planck came along and decided that it isn’t an ultraviolet catastrophe.  In general, theories about stars eventually involve things on an atomic scale, so quantum forces should be considered in how a star forms or how light travels.

Another thing to mention is that by this point we still weren’t totally sure where light from the Sun, and stars in general, came from.    Luckily, we have a whole slew of scientists to thank for figuring this one out.  To start we have F. W. Atson who developed measurements of atoms; his work was used by Eddington to theorize fusion.  Next Hans Bethe, who is given the most credit, gave greater proof that Hydrogen fused into Helium to create enough energy to light up the Sun.  But there is still more.  Since stars have different compositions someone, namely Carl Friedrich Freiherr von Weizsäcker, showed that carbon, nitrogen, and oxygen are involved in fusion for higher mass stars.  Last to note was some heavy news from Fred Hoyle who said that iron can’t fuse into heavier elements, even with such high energies.

Basically, they explained this.

Another person on this long list is Walter Baade.  He looked to the stars, so much so that he found that there were differences between Cepheid variables.  This is linked with the discovery of stellar populations (that he also discovered), that a star’s age affects its composition and overall older and newer stars can be differentiated.  With this, he found that certain Cepheid had different periods, which would change most calculations done before the time that used the variable stars to calibrate distances.  This is why Astronomers must always check their work.

If one read the “Preparing for Competition” part of this blog one may have noticed a certain statement about Swiss Cheese.  But a more important Swiss Astronomer is Fritz Zwicky.  With Walter Baade he coined the term “supernova”, was the first to theorize neutron stars, and proposed that Type Ia supernovae could be used as a “standard candle.”  What this means is that these supernovae can be used to map out extremely large distances because they are all very similar.  Zwicky did work on a galactic scale, literally, since he did work about galaxies, their size, and their mass.  Knowing from Einstein that light mass can bend light he discovered gravitational lensing with galaxies in 1937, which means that we can sometimes see behind galaxies or show that we may have distortions in our views of galaxies.  But even with this he still has his most famous discovery of dark matter.  You know, the other thing they are looking for over at CERN.  Zwicky used something called the virial theorem to show that there is certain mass in galaxies that can’t be seen.  It’s pretty important considering it could make up more of the universe than the regular matter we are made of.

The Coma Cluster, used by Zwicky for finding dark matter. For being called a coma it surely made Astronomers more awake.

With discoveries about galaxies comes another woman, Vera Rubin.  Despite being denied to Princeton, she was able to go to Cornell to gain a higher level degree in her passion of Astronomy.  After trying to decide on a topic, she took to galaxy rotation rates.  It was expected that similar to our own Solar System, the rotation rates would be slower on the outside of the disk of the galaxy than the center.  But after taking spectroscopic data she and her adviser, Kent Ford, found that the edges of galaxies rotated pretty much as fast as the center.  At first it was surprising, but after looking at other galaxies and at the observations made by Zwicky she found further evidence for dark matter.

Chushiro Hayashi was a Japanese astrophysicist, so we know he did something awesome.  He made a contribution to the Alpher-Bethe-Gamow or αβγ paper, which showed how elements were created in the Big Bang and which ones would be more abundant.  He showed that something called electron-positron pairs, which were present in the early universe, should be taken into account.  This led to a more accurate proportion of the presence of elements like Helium.  But besides this his more eponymous discoveries are the Hayashi track and Hayashi contraction, which shows that the evolution of protostars, or stars that are just beginning to develop (not necessarily as cute as babies sadly), can be plotted on an H-R diagram.  The Hayashi contraction itself is when a protostar condenses into a main sequence star;  he showed the temperature at which protostars would maintain hydrostatic equilibrium.