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Astronomer FAQ

Share the Night Sky.

When we hold public events, we get all kinds of questions, which is great!  Here are some of the most common ones:

1.  Is there something special happening tonight?

Usually the answer is no.  Most people are surprised to find that you can set up a telescope on any night and find something interesting to look at.  In fact, it is very common for the planets to line up across the sky in a way that you can see two or three or even more at the same time.  Any even if the planets are not in a good viewing location in the sky, there are dozens of easy to find targets for even the most inexperienced astronomer to enjoy.

2.  How much power does this telescope have?

This is a difficult question to answer.  Usually folks are expecting a magnification or zoom level answer, like “200X”, but this number is not specific to the telescope and the actual zoom level changes with the eyepiece.  In theory, any telescope can be setup to zoom levels as high as 500X or more.  However, the highest useful magnification on a good night is usually around 250X and the eyepiece choice to achieve that magnification depends on the size of the target (planet, star, galaxy, etc.)   A better question might be, “What is the aperture of your telescope?”  Every astronomer can answer that question and it provides a better measure of the capability of the scope.  Aperture is the size of the opening through which the telescope accepts light.  On a reflecting telescope, this would be the diameter of the mirror, and on an refracting telescope, it would be the diameter of the lens.  The more light a telescope can collect, the brighter the image.

3. How much does a telescope like that cost?

A: An Intermediate telescope package, with mount and decent accessories, will run between $1500 and $2500.  That’s not say that you have to spend that to get started in astronomy, though.  You can get a decent Dobsonian mount reflector, with accessories for under $400.  There are even some very nice tabletop models for under $250.

4. Can you see the flag on the moon?

A: Unfortunately, no.  The earth’s atmosphere is a limiting factor for all ground-based telescopes, and even in the best conditions, the smallest features that can be resolved on the moon are more than a mile across.  Even the Hubble Space Telescope, with at least 10 times better resolving power than traditional ground based equipment, is not capable of find the famous flag or any manmade object on the moon.  The only possible exception might be one of the five lunar “retroreflector” units left on the Moon by both the US and Russian moon missions.  These mirror assemblies were designed to reflect laser light back to earth in lunar ranging experiments.  They have been used by observatories, but very few, if any, amateur astronomers have the equipment required to illuminate the mirrors and detect the tiny amount of light returned to earth by these mirrors.

5. What is that bright star I see in the morning/evening?

The bright light you saw was probably a planet, not a star.  Venus is the most likely candidate, as it is often very bright and never gets more than 47° from the sun.  However, it could also be Mercury, Jupiter, Saturn, or Mars, depending on the current alignment and any of these could be seen in the morning or evening, depending on the time of year.

6. How many moons does Jupiter have?

Tricky question.  The correct answer is “lots of them”.  If you were in school before 1974, you might remember the answer to be 12.  However, astronomers are still finding new moons of Jupiter and the current count is up to 79.  The reason is that Jupiter orbits near the asteroid belt, a region of the solar system littered with millions of asteroids, many of which are less than 10 km in size and very difficult to spot from earth.  Most amateur astronomers have only ever seen four moons of Jupiter, Ganymede, Callisto, Io, and Europe, also known as the Galilean Moons.  The rest are simply too dim to see under most conditions and at least 8 inch diameter optics would be required.