Astronomy Telescope Test Review

1. A light year is the distance light travels in one year. Light travels fast, three hundred million meters per sec (300,000,000 m/s) so that distance is very, very large. A light year is a distance unit, NOT a time unit.

2. The objective lens or mirror is the lens or mirror in the telescope. Light hits this before it goes into the eyepiece. The objective causes the light to come to a focus. The eyepiece has a lens that magnifies the image that the objective makes.

3. Focal length = the distance from the lens or mirror to the focal point (or focus); Aperture is the opening of the telescope, which is the same size as the objective lens or mirror. It is usually measured by its diameter.

Focal ratio is the focal length of a telescope divided by the aperture. Magnification is calculated by dividing the focal length of the objective by the focal length of the eyepiece. M = fo/fe

4. A ccd camera takes a picture because light falls on the pixels in the camera. The intensity (or brightness) of the light is measured. The picture is unique because each pixel has information about how much light hit it. You can get that measurement if you use an astronomy image processing program.

5. reflecting telescope, refracting telescope, catadioptric (also called a cassegrain or what we called a combination) telescope

6. A Galilean telescope is a refracting telescope and a Newtonian telescope is a reflecting telescope.

7. Resolution is how well you can see details. Focus is the sharpness of the image. When the telescope is in focus the image appears sharp and you can tell what it is or at least what shape it is. As you move the focusing knob back and forth you are moving the eyepiece so its focus is lining up with the focus of the objective. Chromatic aberration is the little bit of color around the outside of images made with a refracting telescope. An example - An explanation

8. To calculate magnification divide the focal length of the objective (Fo) by the focal length of the eyepiece (Fe). Mag = Fo/Fe

9. MEM is Maximum Effective Magnification. You calculate it by using the "20 times rule" - multiply the diameter of the aperture (measured in cm) by 20. This number is the maximum amount you can magnify with this particular telescope and eyepiece.

10. An image processing program can open a telescope image and read the information about light that is in the image. You can change the colors and brightness of the image. You can also measure how much light is in any pixel. You can also measure size since you can find out much of the sky each pixel covers.

11. The optical system of the eye - opening = pupil, focusing = lens, sensor = retina; The optical system of the telescope - opening = aperture, focusing = either objective lens or objective mirror (also called the primary mirror), sensor = ccd camera or eye

The telescope has a much larger opening or aperture than the eye, so much more light is gathered in a telescope.

The telescope can have a much longer exposure time than the eye. The eye has an exposure time of about 1/15 of a second.

Resolution is much better in a telescope. It can see details and see two objects as distinct at a much further distance than the eye.

The eye has a much larger field of view than the telescope.

The eye can see both in black and white and in color but the telescope can only see in terms of brightness.