Across
- 1. A __ is a “dirty snowball” of ice and rocky debris, typically a few miles across, that orbits the Sun in a long ellipse. When close to the Sun, the warmth evaporates the ice in the nucleus to form a coma (cloud of gas) and a tail. Named for their discoverers, comets sometimes make return visits after as little as a few years or as long as tens of thousands of years.
- 3. When the Moon or a planet appears especially close either to another planet or to a bright star.
- 4. A telescope with a mirror in the back and a lens in the front. The most popular designs are the Schmidt-Cassegrain telescope (SCT) and the Maksutov-Cassegrain telescope (commonly called a “Mak”).
- 5. The diameter of a telescope’s main lens or mirror — and the scope’s most important attribute. As a rule of thumb, a telescope’s maximum useful magnification is 50 times its aperture in inches (or twice its ____ in millimeters).
- 7. An event that occurs when the shadow of a planet or moon falls upon a second body. A solar ___ occurs when the Moon’s shadow falls upon Earth, which we see as the Moon blocking the Sun. When Earth’s shadow falls upon the Moon, it causes a lunar ___.
- 9. The path among the stars traced by the Sun throughout the year. The Moon and planets never stray far from the ___.
- 11. A vast collection of stars, gas, and dust, typically 10,000 to 100,000 light-years in diameter and containing billions of stars (from galaxias kuklos, Greek for “circle of milk,” originally used to describe our own Milky Way).___ may be spiral (with one or more spiral-shape arms), elliptical (shaped more like fuzzy footballs with no distinguishing features), or irregular (chaotic appearance).
Down
- 1. Denotes an object near a celestial pole that never dips below the horizon as Earth rotates and thus does not rise or set.
- 2. A type of Newtonian reflector, made popular by amateur astronomer John Dobson, that uses a simple but highly effective wooden mount. Dobs provide more aperture per dollar than any other telescope design.
- 6. Sunlight reflected by Earth that makes the otherwise dark part of the Moon glow faintly. It’s especially obvious during the Moon’s thin crescent phases.
- 8. The edge of a celestial object’s visible disk.
- 10. Aligning the optical elements of a telescope so that they all point in the proper direction. Most reflectors and compound telescopes require occasional __ in order to produce the best possible images.