h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

I thought I should have somewhere to talk about things astronomical. If this gets unwieldy, I may turn it into an astronomy page.

Last night at about 12:30, when I was putting on the washing and putting out the guinea pigs, I saw two stars through a gap in the clouds to the southwest. They were bright (2nd magnitude at least) didn't look like any two stars close together that I knew.

Checking on Skyglobe this morning, I find that they were probably Regulus (a star in Leo) and Saturn (a planet) which is very close to it at the moment.

I'm impressed Despite having a scope and a book, I've still not really been gripped by star-gazing. About as good as it gets for me is knowing what and where Orion is Oh, and the Pliades.

When we lived half the time on the Great Barrier Reef, we'd spend hours lying on the deck of Bright gazing up into the big skies at night. was very knowledgable and I ought to remember much of what he said, but for some reason it all escapes me now (age).

I have to go out and help a friend but I'll be back to read thoroughly and comment later

Skyglobe is a great program - I got it free with a magazine years ago. It was shareware. If I liked it I was supposed to pay for it. I sent my payment off to the address in the product and it was returned to me as "not known at this address". I did some research on the web, found a new address and did the same again, with the same results. So I've tried - I now consider it mine.

It's a simple program which shows you the stars in any direction at any location in the world at any time. You can run it back to 6,000 BC to see where the pole star was then, or just see what constellations are up above the horizon at the moment.

Unfortunately, it doesn't run on Windows Vista.

There's a useful webpage at http://www.fourmilab.ch/yoursky/ where you can view skycharts, horizon views, track the planets and zoom in with a telescope view from any location on any date. The user interface is a bit clunky because of all the possible options.

Another good one is www.heavens-above.com, although you have to register an email address to use it. They've never sent me any spam, and it's great for identifying satellites and orbiting space junk, and predicting Space Shuttle and ISS passes as well as Iridium flares.

Last night I looked out to the South East at midnight and saw the two main stars of Libra for the first time this year, Zubenelgenubi and that other one.

Zube

There's a useful webpage at http://www.fourmilab.ch/yoursky/ where you can view skycharts, horizon views, track the planets and zoom in with a telescope view from any location on any date. The user interface is a bit clunky because of all the possible options.

Another good one is www.heavens-above.com, although you have to register an email address to use it. They've never sent me any spam, and it's great for identifying satellites and orbiting space junk, and predicting Space Shuttle and ISS passes as well as Iridium flares.

Last night I looked out at midnight and saw the two main stars of Libra for the first time this year, Zubenelgenubi and that other one.

Zube

Whoops!

Zube

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Oh and after Zube: wait! A33827501

GB

I apologise for the incredible segue, but the program sounds like another case of science catching up with science fiction!

Yes, we've had various mechanical representation of the solar system, and for centuries the geo-centric theory created ever more bizarre versions to account for the movement of heavenly bodies, but I distinctly recall a Sci-Fi story about a young man who found he could 'jump' through time.

To aim better, he created a handheld device (with the help of a science devotee friend) to help him determine when he was by matching the position of various nearby stars.

Just thought I'd mention it in hopes that someone remembers the title or author.

I got thinking last night as I dozed off to sleep. How many sixth magnitude stars are there, and how many first magnitude?

I believe that sixth magnitude stars are 100 times as faint as 1st mag ones. That's the way the scale works.

I also know that there are about 5,000 stars visible to the human eye which includes magnitudes 0 up to 6.

I suppose we can assumed that on average all stars are roughly the same brightness, so the variations in brightness are due to distance. The brightness reduces with the square of the distance from earth. So if a +6m star is 100 times as faint as a +1m star, then it is 10 times as far away on average. If we think of the earth surrounded by a number of thin shells, all centred on the earth, then the number of stars in any shell will be proportional to the volume of the shell, which will vary with the distance squared, so there should be 100 times as many stars at 10 times the distance. This leads me to conclude that there should be 100 times as many 6th mag stars as 1st mag stars.

Now for some complicated mathematics to fill in the gaps for other stars.

OK, I've played around with Excel and come up with the following:

+0m 12 stars
+1m 30
+2m 76
+3m 190
+4m 478
+5m 1200
+6m 3,014 stars

It'd be interesting to see does that match the actual number of stars of each magnitude.

'when I was putting on the washing and putting out the guinea pigs' - I have a mental image of you hanging them out to dry!

A table from wikipedia (for what that's worth):


Apparent
magnitude Number
of Stars[93]
0 4
1 15
2 48
3 171
4 513
5 1,602
6 4,800
7 14,000

Zube

That's more 6th magnitude and less of the brighter ones than my calculations. Obviously I should have allowed for a spread in absolute magnitude. The stars we see as 0 or 1 mag are more likely to be brighter than average as well as being close to us.

What size telescope have you got, Zube, and is it a reflector or a refractor?

erm, its a refractor, a general purpose one, not a specialist Astronomical telescope.

Sorry, G, it's a 60 mm refractor, probably cost something like this:

http://www.amazon.co.uk/Tasco-Luminova-578x-Refractor-Telescope/dp/B00009NN16/ref=pd_sbs_ce?ie=UTF8&qid=1211548385&sr=1-148#moreAboutThisProduct

Interesting. According to the Edited Guide, you should expect a magnification of more than 120 from a 60mm scope. That Amazon site gives a magnification of nearly 600!

This one looks good:

http://astronomy.ie/SLTseriesseries.html

#22096 NexStar 102 SLT for €433

Yes, that looks good, 102 mm would make a big difference, and you could still use it to spy on the neighbours!

Cheap telescopes always lie about their max. magnification, if you set them up with the strongest lenses they supply you can see bugger all through them.

I'd love a big dobsonian like one of these:
http://astronomy.ie/dtg.html

Or do you remember the ads in Scientific American?
http://www.celestron.uk.com/catalogues/view_item.asp?ItemID=30679&CatalogueID=272&CategoryID=3824

Little Lotto ticket, it's all up to you!

Zube