Basic Astronomy, Glossary, Objects in Space, Moon

Fig. 18: The Moon. Note the deep shadows in the craters.

BASIC ASTRONOMY

In the early 17th century, Italian scientist Galileo, using a crude telescope smaller than your NG or NGC, turned it to look towards the sky instead of distant trees and moun- tains. What he saw, and what he realized about what he saw, forever changed the way mankind thought of the universe. Imagine what it must have been like being the first human to see moons revolve around the planet Jupiter or to see the changing phas- es of Venus! Because of his observations, Galileo correctly realized Earth's movement and position around the Sun, and in doing so, gave birth to modern astronomy. Yet Galileo's telescope was so crude, he could not clearly make out the rings of Saturn.

Galileo's discoveries laid the foundation for understanding the motion and nature of the planets, stars and galaxies. Building on his foundation, Henrietta Leavitt deter- mined how to measure the distance to stars; Edwin Hubble proposed a glimpse into the origin of the universe; Albert Einstein unraveled the relationship of time and light. Almost daily, using sophisticated successors to Galileo's crude telescope, such as the Hubble Space Telescope and the Chandra X-Ray telescope, more and more myster- ies of the universe are being solved and understood. We are living in the golden age of astronomy.

Unlike other sciences, astronomy welcomes contributions from amateurs. Much of the knowledge we have on subjects such as comets, meteor showers, variable stars, the Moon and our solar system comes from observations made by amateur astronomers. So as you look through your telescope, keep in mind Galileo. To him, a telescope was not a mere machine of glass and metal, but something far more—a window of incred- ible discovery.

The Glossary

Be sure to make use of the Glossary feature in your NGC computer control panel. The Glossary menu provides an alphabetical listing of definitions and descriptions of com- mon astronomical terms. Access directly through the Glossary menu or through hypertext words. See GLOSSARY MENU, page 17, for more information.

Objects in Space

Listed below are some of the many astronomical objects that can be seen with your telescope:

The Moon

The Moon is, on average, a distance of 239,000 miles (380,000km) from Earth and is best observed during its crescent or half phase when Sunlight strikes the Moon’s sur- face at an angle. It casts shadows and adds a sense of depth to the view (Fig. 18). No shadows are seen during a full Moon, causing the overly bright Moon to appear flat and rather uninteresting through the telescope. Try using a neutral Moon filter when observing the Moon. Not only does it protect your eyes from the bright glare of the Moon, but it also helps enhance contrast, providing a more dramatic image.

Brilliant detail can be observed on the Moon, including hundreds of lunar craters and maria, described below.

Craters are round meteor impact sites covering most of the Moon’s surface. With no atmosphere on the Moon, no weather conditions exist, so the only erosive force is meteor strikes. Under these conditions, lunar craters can last for millions of years.

Maria (plural for mare) are smooth, dark areas scattered across the lunar surface. These dark areas are large ancient impact basins that were filled with lava from the interior of the Moon due to the depth and force of a meteor or comet impact.

Twelve Apollo astronauts left their bootprints on the Moon in the late 1960's and early 1970's. However, no telescope on Earth is able to see these footprints or any other artifacts. In fact, the smallest lunar features that may be seen with the largest tele- scope on Earth are about one-half mile across.

Planets

Planets change positions in the sky as they orbit around the Sun. To locate the plan- ets on a given day or month, consult a monthly astronomy magazine, such as Sky and Telescope or Astronomy. Listed below are the best planets for viewing through your telescope.