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

Does "Dobsonian" indicate that it is not an equatorial mount? Wouldn't that make it rather hard to track things?

Another thing not considered when talking about brightness fading with distance is interstellar dust. some directions are dustier than others which cuts down the magnitude.

If dust is uniform, does brightness decrease with the square of distance?

Yes, the Dobsonian design uses a simple altazimuth mount to save cash. Not great for photography.

So, good for galaxy watching but not good for planets. I remember spending about 20 minutes aligning the telescope at 200x to see Saturn. It stayed in view for about 2 seconds and then it was gone again and I couldn't find it.

Hi Gnomon

If I read it aright, and perhaps I’ve misunderstood you, I think that your initial assumption might be awry.

>I suppose we can assumed that on average all stars are roughly the same brightness,<

Stars vary considerably in their actual brightness, Our grading in ‘apparent’ magnitude is only as we perceive them, The brightest star we see is Sirius. Compare this to the current known actual brightest star: http://hubblesite.org/newscenter/archive/releases/1997/33
Which we are unable to see without the aid of the hubble telescope.

It releases 10 million times the amount of light that our sun does and it’s big enough to fill the Earth’s orbit. It is 25,000 l/y away and would appear 4th mag if it wasn’t for the dust between us. Sirius is only 8 l/y away but shows as a first mag star.

Deke

Thanks, Deke. I think I came to that conclusion in posting 14.

Oops. Sorry.

Deke

No, that's ok. I wasn't being sarcastic, and am genuinely grateful for your comments.

I should have read further.

I've had a few looks through the telescope in the last couple of weeks and I'm beginning to know how to work the controls. The problem now is waiting for a clear night when it is dark. These days, it doesn't get really dark until about 11:30. I've two eyepieces, a 25X (25 magnifications) to see a broad view and a 75X for detailed work. I've ordered two more, a 17X for really broad views (useful for looking at loose clusters like the Beehive) and a 170X for even more detailed work. I'll get these in a few weeks.

So far I've seen:

Saturn - although it is very small at 75X. I can just make out the rings.

Epsilon Lyrae - a double star which is quite striking. It's actually a double double - each of the two stars is itself a double, but at 75X I can't see that.

Mizar - this is a very spectacular double, being a bright star to start off.

The Moon - the new crescent moon is very spectacular at 75X, although I didn't look for long; I was really only testing the telescope.

Praesepe - the Beehive cluster - this is impressive but will benefit from the wider view of the 17X when I get it.

M57 - the Ring Nebula - at 75X on a rather cloudy night, this was right on the limit of my vision. When I looked straight at it all I saw was a blob. Looking out of the side of my eye I could see a ring.

The skill is knowing what to look for. If I let my eyes get used to the dark, then I can't consult a book to see what's interesting in the area, so I have to swot up on what might be visible before I go out. And star charts don't tend to list which things are visible in a 4 inch telescope at 75 magnifications. So a few of the galaxies which I asked the telescope to display just appeared as black sky.

But I'll get used to it with a bit of practice.

If you like doubles, Beta Cygni is a fantastic one to look out for. Very marked colour difference between the stars and easy to find.

Turn Left at Orion is written with small telescopes in mind and also uses sketches of the view of the objects that you're looking at so you have some idea about what you're looking for.

You'll need to get yourself a small low power red torch to help see your way around outside in the dark.

Thanks Phil. Beta Cygni should be easy to find this time of year.

Here, nebulae and galaxies are always the most difficult of objects to find. Living on the edge of London it’s always difficult to get a clear enough night to see anything of that nature, I can count on the fingers of one hand the number of times I’ve positively identified the Ring Nebula or the Crab Nebula. I’ve never been able to see them with binnies, even on the few occasions I’ve stayed out in the country. The Ring nebula I’ve positively been able to see the colours, but not the Crab.

Spiral or any other sort of galaxy I’ve mostly only been able to see as a slight patch of light without making out any real form. Perhaps that’s why I tend to concentrate on the Moon. No shortage of light there.

One of the more fascinating objects are the globular star clusters. The most prominent one in this hemisphere is at its most, er prominent, at the moment. M13 in Hercules is quite high at the moment and worth a look. I often wonder what the night sky might be like on a planet in the middle of that .

Later this year I’ll try for that other Nemesis of mine, the two outer planets Uranus and Neptune. Neither are well placed but it might just be possible to make an acquaintance again,

It was a bright, clear morning as I walked to work today, and there was a drop-dead gorgeous crescent moon in the pre-dawn sky, nail paring thin and hanging there in the blueness.

Last night, I saw Jupiter and Venus together. Venus was very low so I couldn't see with the telescope on the deck, so I lugged the telescope upstairs to Iz's bedroom and tried to look out through an open window, but the tripod is quite bulky and I couldn't manage it. As far as I could see, though, Venus is not a crescent at the moment.

I'd a quick look at Jupiter too but then the clouds came.

If you get chance (and good weather) tonight after sunset, Venus, Jupiter and the will all be in the same general direction. Should be quite a sight

The moon will actually occult Venus _before_ sunset but we won't see that

Venus and Jupiter were very spectacular together last night, but unfortunately so low down that I couldn't see them with my telescope. I also saw the new moon, as thin as you could imagine in a light blue sky so it must have been just after sunset.

I'll be out there with my binos soon, but it's not looking very promising

According to my Stellarium, the moon is occulting Venus right now.

I don't get home till about 5pm, so I won't have a chance to look until then, and I won't have much time even then, as I have to cook a meal and then head out again at about 6pm.