A Landing a Day

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Posts Tagged ‘Vesto Slipher’

Mulberry, Indiana

Posted by graywacke on February 8, 2016

First timer?  In this formerly once-a-day blog (and now pretty much a once-every-three-or-four days blog), I have my computer select a random latitude and longitude that puts me somewhere in the continental United States (the lower 48).  I call this “landing.”  I keep track of the watersheds I land in, as well as the town I land near.  I do some internet research to hopefully find something of interest about my landing location.  To find out more about A Landing A Day (like who “Dan” is) please see “About Landing” above.  To check out some recent changes in how I do things, check out “About Landing (Revisited).”

Landing number 2245; A Landing A Day blog post number 673.

Dan:  This is my first landing in Indiana since changing my random lat/long landing procedure 29 landings ago.  And yes, my Score went down (from 1132 to 1113).  If you’re curious what I’m talking about, check out the “About Landing (Revisited)” tab above.

Here’s my regional landing map:

landing 1

And my local landing map:

landing 2

You can see on the above map that I landed in the watershed of the S Fk Wildcat Ck.  My streams-only map shows that the S Fk discharges to Wildcat Ck; and on to the Wabash R (26th hit):

landing 3a

Zooming back, you can see that Wabash (which forms a good portion of the IN/IL boundary) ends up in the Ohio R (136th hit):

landing 3b

Of course, this is all part of the Mississippi watershed (880th hit).

Click HERE for my Google Earth (GE) spaceflight in to central-ish Indiana.  After enjoying the flight, hit your back button.

I have excellent GE SV coverage:

ge sv landing map

Here’s what the orange dude sees:

ge sv landing

And I get a good view of the S Fk Wildcat Ck:

ge sv creek map

And here ’tis:

ge sv creek

Since Mulberry was the closest town to my landing, it was the first town I checked out.  It was looking absolutely hookless until I saw this name under “Notable People:”  Vesto Slipher, astronomer.

Two things jumped out.  First, what an incredibly strange name; and secondly, he was an astronomer with his own Wiki entry.  It turns out that he was quite accomplished and he played a key role in understanding one of the most fundamental aspects of our universe. 

This is going to be my first straight-ahead astronoomy post.  I’ll meander a bit, before pulling Vesto in to the story.  So what fundamental aspect of our universe do I have in mind?  It’s the fact that the universe is expanding.  This, of course led to a cornerstone concept in modern cosmology:  running the clock backwards inexorably leads to the Big Bang.  So how was this all figured out?

You’re probably thinking that Edwin Hubble figured it out, and that’s fundamentally true.  He’s the guy who developed Hubble’s Law, which quantifies the relationship between galactic distances and the speed that the galaxies are flying away from us.  Simply put, the farther away the galaxy, the faster it is receding from us.

Interesting sidebar:  If you think about it for a moment, it would be perfectly logical to conclude that we’re at the center of the universe.  After all, hundreds of billions of galaxies that make up the visible universe are all flying away from us, at velocities that are proportional to their distance from us.  What other conclusion could be drawn? 

Well, here’s the rub.  An observer on a distant galaxy, making the same measurements that I just described, would also find that all galaxies were flying away from him, also at speeds proportional to distance.  This is one of those total head-scratchers that I like to think about, but am at a loss to truly understand.

So anyway, Hubble needed two critical pieces of information:  first, the distances to galaxies (which was his strength and the center of much of his research); and secondly, the relative velocity of galaxies as observed from Earth (i.e., are they moving toward us, moving away from us, or staying put?  And how fast?)

Hubble was a leader in using “standard candles” to determine galactic distances.  A standard candle is an identifiable light source that, no matter where it is, shines at a known luminosity.  The farther away it is, the dimmer it appears; but since the actual luminosity is known, there’s a formula that can be used to determine the distance to the light source. 

Well, it turns out that there’s a type of star known as a Cepheid variable that can be identified by the way the intensity of the light varies.  It turns out that there’s a direct relationship between a Cepheid variable’s luminosity and pulsation period.

So Hubble used Cepheid variables to determine the distance to hundreds of galaxies, all of which had identifiable Cepheid variable stars.

Note:  Cepheid variables are good up to a distance of about a million light years.  To find out about galaxies further away (which is the vast majority of galaxies), a Type 1A supernova is often used as the standard candle.  This is much tougher job, as supernova are rare transient events and it takes a lot of work to find enough of these to build up a statistically significant data base.  But legions of persistent astronomers have done that and, of course, have found that Hubble’s Law holds true all the way to the far “edge” of the universe . . . 

Anyway, back to Hubble’s discovery:  it’s this second question (the relative velocity of galaxies) where he leaned heavily on the research of our hero, Vestos Slipher.  So what did Vestos do?  First some background. 

It turns out when light is passed through a prism, it looks like this:


This is the visible light spectrum (a rainbow).

The light spectrum from stars and more distant galaxies does not look like the continuous spectrum shown above.  Rather, it has distinct spectral features characteristic of the atoms in the gases around the stars.  Because hydrogen is far and away the most abundant element in the universe, hydrogen impacts the way the spectrum looks, thusly:


The black lines in the absorption spectrum are gaps in the spectrum created as light passes through hydrogen gas.  The Hydrogen Emission Spectrum is the opposite:  it shows corresponding narrow bands of light emitted as the light passes through.  

OK, OK.  I’m on pretty shaky ground here.  I’m ignoring the quantum mechanics that explains why these absorption and emission wavelengths exist at all (and why there are both absorption and emission spectra).  Suffice it to say that these hydrogen spectra can be discerned and measured by analyzing the light from stars and galaxies.  Moving right along:

When the light source is traveling away from us, the light wavelengths become longer, as the wave appears to be stretched out. This is a Doppler Effect, just like the changing sound of a train whistle as the train goes by (a higher pitch when the train is approaching and a lower pitch when the train is receding).

The faster the relative speed of a receding galaxy, the longer the hydrogen spectrum wavelengths become.  This “shift” is towards the red end of the spectrum, and is therefore known as red shift.

The magnitude of the shift is determined by looking at the hydrogen emission spectrum at rest and comparing it with the spectrum from the moving galaxy.

Here’s a graphic showing how the hydrogen spectra are shifted when measured from a rapidly-receding galaxy (from Georgia State University):

red shift

See the “v=-.1c?”  This says that a galaxy receding at one tenth the speed of light results in the red shift shown.

Phew.  So good ol’ Vesto was a pioneer in identifying and measuring the red shift of hydrogen emission spectrum wavelengths emanating from galaxies and realizing that this shift has to do with the relative velocity of the receding galaxy (and is a way to measure the speed of the receding galaxy).

So, one part Hubble (galactic distances) + one part Vesto (relative galactic velocities) = Hubble’s Law.  I wonder how close Vesto was to coming up with the overall theory?  If he were a little quicker, maybe we’d have the Slipher Space Telescope . . .

Time to close this unusual post out with my usual GE Pano shots.  Taken along the railroad south of Mulberry, here’s a shot (by Refidini-Nip-Kosove) of an eye-catching rail tank car:

pano refedini-Nip-Kosove

I’ll close with this great sky shot by Ana Buzancic, taken less than a mile south of my landing:

pano Ana Buzancic Petercic

That’ll do it . . .




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