Answers for the Most Asked Question Around the World

Which orbits are used for space telescopes?

Launching into space is enormously costly and difficult, so deciding where to locate an observatory must be a compromise between astronomical advantages and the payload capabilities of the launch systems. Purely from the viewpoint of the energy required for launch, the “Low Earth Orbit”, at an altitude of about 500 km, is the most economical…. read more »

How is a space telescope pointed?

Action/reaction . . . remember? On Earth, if you want to move a piece of furniture, no problem: you just brace your feet against the floor and push. And a motor rotates a telescope by bracing against a part of the mount that is fixed to the ground. But in space? – nothing to brace… read more »

What can we learn from observations at radio wavelengths?

Observations at radio wavelengths are highly informative because they allow us to see things that are not detectable in the optical. Radio waves pass easily through gas and dust clouds, so stars or galaxies that would be invisible to an optical telescope can be seen at radio wavelengths. Certain regions of the Universe contain molecules… read more »

What can be learned by observing at x-ray wavelengths?

The x-ray Universe is very different from the visible one as x-rays are produced only by matter that has been heated to temperatures in the millions of kelvins. And this occurs only in the presence of extremely powerful magnetic or gravitational fields, or during explosions. See Q. 156 for a view of the Galaxy in… read more »

Interested in amateur astronomy? What are the first steps?

Astronomy is not just for professionals – the sky belongs to everyone! Amateur astronomy is a fascinating hobby, running from the simple pleasure of gazing at the night sky, to learning to appreciate the phenomena and mysteries of the Universe, all the way to making quasi professional observations. Perusing books and magazines on astronomy, even… read more »

What can be seen with an amateur telescope?

It all depends on the telescope aperture and the observing conditions – darkness of the sky and atmospheric turbulence. Here are what you can hope to view when conditions are good. With a 60 mm (about 2 in) refractor: the surface of the Moon, the phases of Venus, sunspots (with a filter in front of… read more »

What are the Messier objects?

The Messier objects are the delight of amateur astronomers. The French astronomer Charles Messier (1730–1817) was a dedicated comet hunter. Systematically searching the sky for non-stellar objects, he found a number of diffuse objects that he soon realized could not be comets because they did not move. To help other comet hunters in their searches,… read more »

How can planets be spotted in the night sky?

If you are out in the field and are unable to access one of the many sky maps available in magazines or on the Internet, the planets can be difficult to pick out from among the many bright stars. The only ones visible to the naked eye are Venus, Mars, Jupiter, and Saturn (Mercury requires… read more »

How can you find an amateur astronomy club?

It is easy to become a member of an amateur astronomy club, even if you do not own a telescope. There are clubs in most relatively large cities around the world, usually sponsoring monthly activities that include talks, workshops, and observing sessions. A search on the Web is likely to find a club based near… read more »