Friday, July 3, 2009

Daytime Observing with Your Telesccope

You can get plenty of use out of a telescope for astronomy even if it's not dark out. First, it's important to not use your telescope to look at the Sun unless you've got the right equipment. That means a full-aperture solar filter for starters, removing any finder scopes from the telescope, and a good knowledge of what you're doing otherwise. Those little solar filters that screw onto the eyepiece are not safe. They can crack from the heat of the concentrated sunlight on them, and if you're eye's there when they do crack, you'll get the full force of the sunlight it lets through on your retina. Not good.

There are plenty of things to look at other than the Sun, however, that don't require any special preparation of your telescope. The Moon is often up in the daytime, and while it doesn't show its detail as sharply through a daylit sky as at night it's still very interesting to look at. Just as at night, the best area to look is along the line between the day and night parts of the Moon, what's called the "terminator".

Several planets can also be observed during the daytime. Mercury is always close to the Sun, and Venus never gets too far away. Finding them during the day is the problem since they don't stand out as well as they do at dusk or in the night. If you have a chance, it's good to get familiar with where they are when you can see them easily, before you go out to find them in the daytime. Use their location with respect to the Sun as a reference, since that'll be your biggest signpost in the sky during the daytime.

Then, when you go to find it during the day you can start out with the end of the telescope covered, as well as any finder scopes. Start at the Sun, then move away from it. Stop before you get to where you think you need to be for the planet, uncover, and then move toward the planet while moving away from the Sun. Never move back toward the Sun while you're looking through the scope. It's also a good idea to have a second person on hand to make sure you don't move the scope back toward the Sun while looking through the telescope.

If you've got a computer on your telescope, that can put you on the planet once you get it aligned. If you have an alignment procedure that will work with you levelling the scope, setting it to north, and using the Sun as a reference point (line up the scope with the Sun with the covers on it and the finder--use the shadow of your scope to line up on the Sun, and don't look through it!)

Venus can show very nice phases during the day, looking like a little Moon.

Jupiter and Saturn can be seen during the day as well, they look like ghostly versions of themselves during the day. Seeing them during the day is quite an experience.

You can also see the brightest stars during the daytime. Sirius, the brightest star (other than the Sun, of course), is the easiest to see. Arcturus, Fomalhaut, Betegeuse and Rigel can all be seen in daylight as well.

You'll want a clear sky, with as little moisture as possible. The deeper the blue at the highest point in the sky, the better your chances.

Give daytime observing a try, and see how many "night time objects" you can collect!

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