Okay, the Southern Skies Star Density thing is SETTLED! But Mike challenges the Astronomy World with his new theory of why the night sky is dark!

Definitely click for bigger & clearer.

The argument about the density of the star population in the Southern skies vs. the Northern skies Has Now Been Settled. Please pay particular attention to the first three words of Dr. Matthew Colless' thorough, generous and prompt reply to Vleeptron's plea to settle this controversy: "You are right ...", and by "You" Dr. Colless means Me.

I knew the shape of the Milky Way. I'm just a crappy draftsman and couldn't figure out how to make MSPaint sketch a bulging discus. Cylinders, disks and hockey pucks I can handle.

Now for Olbers' Paradox. Mike wrote:

Perhaps it's arrogant of me to disagree, but I disagree. Not with you Bob, as this is a very interesting theory, but with the theory in general.

The theory assumes that there's a bunch of lights at a distance, and they're shining right at us with nothing in the way. That's just not the way the Universe is designed. Given the vast (understatement) size of the Universe, you have to assume that even if there's a light source out there, the direct line of sight between it and us is broken a huge amount of times by any number of objects. Dead stars, planets, gas clouds, comets, meteors, etc. All of these objects break down the light and send it off into other directions.

I read the entry on Wikipedia on this, and I did note the Absorption portion of the article, and it's ideas. I disagree with it too (I guess I'm one of those non-scientist people). The objects that "absorb" the light would re-radiate that light. This is true. But it re-radiates it uniformly (I'll get to this in a second). The small portion of the light that should have gotten to Earth is broken down into even smaller portions, and this happens an unknowable number of times between here and there. Also, the Universe is not infinite in size. Some of this light (I'd argue a majority of it) gets pointed away from all other objects. Even though the energy is conserved, it's not light that we'll see. Ever. What this comes down to is even though the light is out there, it's not coming at us, or it's to faint to see. As for the uniform radiation theory, I'm not sure I buy that either. Light reflects. it bounces off of things and goes in different directions.

The human eye can only see so much. The light of a candle is lost at 43 miles. Sure, that's a long way for so little light, but it's not that the light isn't reaching you. How long does it take light to go 43 miles? I'm not going to figure it out, but it's not very long.

I was reading something about Galaxy clusters the other day. There's a pretty cool picture at

http://www.astrographics.com/GalleryPrintsIndex/GP0017.html

This picture is taken with a pretty amazing telescope. Can humans see it with no aid? Nope. Is the light getting here? Yep. But if we were to look right at it, we wouldn't register a thing.

If you look at the night sky on a night with no moon, the sky isn't black. It doesn't even look black. It's a dark blue. Very, very dark. Why? Because there's light there. Not much, but some.

Another thing to consider, even at as lame a distance as 4.3 light years away, our Sun is just a bright star. Dimmer than Serius. What would our Sun be after 10 light years? 50 light years? 1000 light years? That's just 1000 years out of 4.5 billion years old. It's not that the light isn't getting there. It's there. It's just not going to be bright enough to be seen.

OK, now that I've typed a lot, and proven to the world how stupid and stubborn I am, I'll stop typing.

You got guts, I got to say that. Never mind me -- I'd believe anybody who waved a Ph.D. in astronomy around. If they told me the night sky is dark because somebody forgot to pay the electric bill, I'd believe it.

But you're taking on Edgar Allan Poe, Albert Einstein, Edwin Hubble, Fred Hoyle, and whoever wrote the Wikipedia wiki. The best explanation I ever sucked down of the Solution to Olbers' Paradox was in Hoyle's "Frontiers of Astronomy" (1955). But Hoyle rejected the Big Bang, and was a Steady-Stater. So in modern astronomy, there's a little wiggle room for what you believe.

But maybe they're wrong and you're right. In which case I want an invitation to Stockholm to be there when you accept your Nobel Physics Prize. (Al Gore just got to meet Uma Thurman, she was the celebrity hostess of his apres-Nobel party!!!) Everybody was sure Newton's scheme of Space and Time was the Real Deal, and then Einstein (a low-level patent examiner in the Swiss Patent Office) cooked up his very different Relativity. Keep kicking. It could happen.

Now back to the Southern night skies. The Anglo-Australian Observatory runs one of the world's most powerful optical telescopes in a tiny dot called Siding Springs in the Back of the Beyond in New South Wales, Australia. They put it so far out in Nowhere that it's about as free of light pollution as any place you can find in this dirty world.

When the Director of the Anglo-Australian Observatory looks up at the night sky, he's looking at the Southern skies, and I am guessing he's something of a reliable authority on them. Here is my plea to settle this dustup, e-mailed Friday morning, and his same-day reply.

I think Dr. Colless has a soft spot for people who spell well, use good grammar, say Please, and are genuinely curious about astronomy.

Actually I'm 2 for 2 with nice, prompt, personal answers from world-class astronomers; the Japanese comet expert Seiichi Yoshida answered my question about when Comet McNaught would come back again. (Like the realistic equivalent of Never.) I have a feeling that astronomers enjoy a little dialogue with curious amateurs. Every great astronomer began as an 11-year-old curious amateur, and they remember the days when they were as Dumb As Bob, and needed their questions answered.

Got tough science questions? The Vleeptron High Non-Junk Science Council goes to the center of the Outback to get you The Authoritative Answer!

==============

Dr. Matthew Colless, Director

Anglo-Australian Observatory

Dear Dr. Colless,

Please pardon this space invasion. I'm an amateur and a great admirer of the AAO and the work it does.

I travelled to Alice Springs to see Comet Halley. It was the first time I'd ever seen the Southern skies. They were obviously startlingly different from my Northern skies, but also seemed denser and richer. One of our Alice Springs hosts who provided us with telescope time explained that this was a function of the rotational orientation of the Earth -- that the South just always points to a denser star field within the Milky Way.

Now my blog pals and I have stumbled into controversy, and one claims the Southern skies are not inherently more star-dense than the Northern; but that what I saw was only a seasonal phenomenon, which would have reversed six months later. (I think our visit was in March.)

The controversy, and our pathetic theories and diagrams, are at

http://vleeptronz.blogspot.com/2007/12/does-southern-hemisphere-always-get.html

Could you spare us just a few moments to Make Us Smart about this question? There are admittedly limits to how much smarter you can make potzers like us, but any help you can offer would be greatly appreciated, and received as a great treat.

Wishing you the happiest Holiday season and New Year,

Bob Merkin

Northampton Massachusetts USA

P.S. The night before we took the Ghan [train] from Adelaide, the TV weather report said Alice Springs would be "grouse." I thought it was an advisory for bird hunters.

===================

----- Original Message -----

From: Matthew Colless

To: bobmerk@earthlink.net

Sent: 12/22/2007 1:22:08 PM

Subject: Re: Question about star density of Southern skies

[NOTE: R.A. = Right Ascension, one of the two numerical values used to aim at a specific sky direction. The other is Declination.]

Hi Bob,

You are right about the southern skies having denser starfields than the north overall, though it does rather depend where you look and when. The main reason for the difference is that the centre of the Milky Way is in the south (Declination=-29 degrees). Our Galaxy is not so much a disk as a discus (thinner at the edges than the centre) with a fat hub (the Galactic bulge). When the Galactic centre is high in the southern sky (R.A.=17h45m, so our winter, your summer) the total number of stars visible in the sky is much higher than can be seen in the north (the number of bright, nearby stars only a little higher; the number of faint, distant stars is much higher). The star fields near the plane of the Galaxy are a fact of a few to several times denser near the Galactic centre than towards the rim; but the Galactic poles (north and south) are fairly similar. And of course during the southern summer the Galactic centre is mostly below the horizon at night, so the difference between hemispheres is much less. Actually one of the biggest differences between Australia and the US is the lower population density and hence lower light pollution - it is easier to get out of populated areas in Australia and find truly dark skies, and so see more stars.

Regards, Matthew.

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Professor Matthew Colless
Director, Anglo-Australian Observatory
Tel: +61-2-9372-4812
Fax: +61-2-9372-4880
P.O. Box 296, Epping, NSW 1710, Australia
Email: colless@aao.gov.au
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