You may have heard the term "astronomical telescope" and are wondering what it means.

It is a bit of a loose term and it refers to two different things.

In a nutshell an astronomical telescope is a telescope that is specifically designed for and made for astronomy use. I know that sounds a bit funny but take a look at this telescope:

It is very big! And it is mounted in place. It can't easily be pointed at objects on the earth. It has a dome around it! This telescope is made specifically as an astronomical telescope.

Astronomical telescopes also are designed specifically to gather as much light as possible. So typically they have very big lenses or mirrors.

Star light and light from other celestial objects is extremely dim. Large optics are needed to gather as much light as possible.

Another thing about an astronomical telescope is that it usually has someway to compensate for the motion of the earth.

What I mean is this:

If you point a telescope at a building down the street the building doesn't move. You just have to hold the telescope steady.

But the objects in the sky do move! They do a complete revolution every 24 hours. So, an astronomical telescope will often have some kind of mechanical device to move the telescope. It will follow the stars!

This picture here shows some parts of an astronomical telescope. Number 6 is a motor that rotates the telescope so it can follow celestial objects.

One more thing to note if you are buying a telescope.

I had earlier mentioned that gathering as much light as possible is important for an astronomical telescope. This means big mirrors and lenses right? But it also means as few lenses and mirrors as possible.

An astronomical telescope sees things upside down. Yes, if you look at a star with it the star is upside down. Or if you look at the moon it is also upside down. But it doesn't really matter.

But if you look at the house down the street you don't want it to be upside down!

So, if you are buying a telescope that is specifically astronomical you may have to also buy an extra optical piece called an erecting prism to flip the image back to right side up - if you want to use your telescope for observing things on the earth - things like the house down the street.

Just keep that in mind when buying a telescope. If you are going to use it solely for astronomy then the extra lens is really unnecessary, and even unwanted because it does reduce the amount of light your telescope gathers.

Astromania 1.25" 90-degree Erecting Prism

• This is a great diagonal for daytime terrestrial use and night time astronomy applications for telescopes or spotting scopes.
• High quality optical Prism inside rather than a mirror which makes your image clear and sharp.
• Economical 1.25" 90-deg prism diagonal for astronomical telescopes and spotting scopes.
• More comfortable viewing orientation as you observe from above, filter thread for any 1.25" filter. Accepts standard 1.25" eyepieces.
• With this diagonal you can match the orientation of the star field with "correct" star maps and charts. It produces an image that is oriented properly, which means that the image is upright but reversed left to right.

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