What is a planisphere and do I need one. A planisphere is simply a tool we use to find our way around the sky. It consists of 2 circles, one has a sky map printed on it, the second has a window cut into it which allows only the part of the sky visible in the sky at the intended point in time to be seen. The masked circle is marked off in a 24 hour clock configuration, while the sky map portion is marked of in the 12 months of the year, subdivided by day.


To see what is in the sky on the day and time you want to observe at simply line up the day and time and the sky chart will display the objects that are visible. Simple, easy to carry, and very efficient. I used one when I was starting out, and still use one to this day. A planisphere is especially handy for quick, grab and go sessions or binocular observing.

Orion makes a beauty that I can highly recommend: Orion Star Target Planisphere

If you look at the advertisments and packaging for astronomical telescopes they almost always show gorgeous, vivid color pictures of nebulae and planets, etc. But can you really see color at the eyepiece. Another yes and no answer.

You will not see the brilliant colors or detail visible in those pictures. These were shot with sensitive film or specialized digital detectors (CCD cameras) which collected photons for minutes or hours. Your eye can not do that. What you do see through the eyepiece is subtle, yet beautiful in its own right.

Another reason for the lack of color is when your eyes have 2 sensors, rods and cones. The cones are responsible for color reception, the cones do great with even dim light. When your eyes are dark adapted, the rods dominate and color detection goes down.

On M42 for instance (the Orion Nebula) at a dark sight I usually see it as a pastel grey/green with almost any scope. However with bigger apertures (14 inches and up), I do detect a bit of peachy pink, kind of a rose tint, and a touch of blue but it is subtle. I have also detected some color in the brighter planetary nebulae. Definite color can be seen in some stars, especially double stars with different colors which gives a nice comparison.

Also color is nicely evident on the planets, but they again are more pastel than vivid like you see in pictures. Details in any view have to be teased out while you observe, the longer you look, the more you see. Another trick is to use averted vision when viewing deep space objects. By this I mean you look at the object but don't look right at it (off to the side of your vision kind of. Try it at the eyepiece.

Clear Skies

This post is brought on by seeing cheap little telescopes being advertised as offering 500X magnification and other such nonsense.

First off a telescope alone doesn't give any magnification. An eyepiece, working in concert with the telescope does that. A telescopes function is to gather more light than your eye can, and focus that to a spot where you can then utilize an eyepiece to magnify the image.

The amount of magnification achieved is calculated by the focal length of the telescope divided by the focal length of the given eyepiece. So with my 8inch SCT which has a focal length of 2000mm if I use a 10mm eyepiece we get 2000/10=200X. Pop in a 25mm eyepiece and 2000/25=80X. Now lets look at my 90mm refractor with the same 2 eyepieces. The refractor has a focal length of 600mm so 600/10=60X and 600/25=24X.

Now on to the point I made that the claims of 500X from a small telescope are nuts. Is 500X possible, yes. But it is not usable. A good rule of thumb is that the MAXIMUM usable magnification you can use is 50X per inch of aperture. And that is on the best, steadiest nights. Normal usage is more in the 30X per inch of aperture. So the best magnification I could realistically look at in my SCT is 8*50=400X. So these little cheapo department store telescopes with their 60mm of aperture which is about 2.5 inches would have a maximum usable magnification of 2.5*50=125X. And the eyepieces that come with these are usually crap as well so you won't even get that.

Trust me, don't waste your money, save up and buy a proper scope with some good eyepieces. You will be glad you did. While you're saving up, get a planisphere, learn the constellations, and do some scanning with binoculars.