What to Observe in the Night Sky

The Moon

The moon is the nearest object to view. It is bright and easy to find. It is best to view the moon when it is not full. The most dramatic features can be seen at the edge of dark and light, day and night on the moon. This is where the shadows from craters and mountains are most defined.

Planets

Some of the planets are easy targets too. They also can reap rewarding views with somewhat minimal effort. Jupiter and Saturn are very impressive even in a small inexpensive telescope.

The first thing you need to do is find out where they are in the night sky. The planets closer to the sun change their position in the night sky quicker than those further away. Once you know where Jupiter and Saturn are you pretty much can count on them staying in the same area for a few months. Mars is also a popular target. Mercury and Venus orbit inside Earth's orbit, so they never stray far from the Sun in our sky, and in a telescope they show phases like the Moon, from a thin crescent to nearly full. Uranus and Neptune are difficult to find and see.

There is plenty more information on observing planets in the Solar System section.

Double Stars

These are stars that are apparently so close together that they look like one star to the naked eye. When a telescope is used you can see that there are actually two stars or even three or four.

One of the most dramatic double stars is Albireo. It is in the constellation Cygnus. To the eye it looks like a single yellowish star. In a telescope we can see that there are two stars, one golden orange and one blue. The orange one is a giant star, and the blue one is a hotter, smaller star.

Star Clusters

There are two types of star clusters

Open Clusters - These are patches in the sky with lots of stars. They are loosely gathered and randomly arranged. Some of these clusters have shapes that can be seen using your imagination. Some of these shapes have given some clusters names describing the shape (Beehive, Christmas Tree, Owl...)
Globular Clusters - These are clusters that are spherical and held together by gravity. Some globular clusters have millions of stars. For northern observers, the most popular and easy to find globular cluster is M13 in the constellation Hercules.

Nebulae

The word nebula means cloud. Nebulae are clouds of gas and dust; most of the ones we see shine or reflect the light of nearby stars. Nebulae are more difficult to see than the objects mentioned so far. It is best to use a large aperture telescope to view them.

There are five types of nebulae

Planetary Nebulae - These nebulae are shells of gas thrown out by some stars near the end of their lives. They are called planetary nebulae because they often look a little like planets in small telescopes. A typical planetary nebula is about a light-year across.
Reflection Nebulae - These nebulae are clouds of dust which are reflecting the light of nearby stars. They are usually blue because the scattering is more efficient for blue light. Reflection nebulae can be huge and are often the birthplace of new stars. Reflection nebulae and emission nebulae are often seen together and are sometimes both referred to as diffuse nebulae.
Emission Nebulae These nebulae are clouds of high temperature gas. The atoms in the cloud are energized by ultraviolet light from a nearby star and emit radiation as they fall back into lower energy states. These nebulae are usually red because the predominant emission line of hydrogen happens to be red. Emission nebulae are usually the sites of recent and ongoing star formation.
Dark Nebulae - Dark nebulae are clouds of dust which are simply blocking the light from whatever is behind. They are physically very similar to reflection nebulae; they look different only because of the geometry of the light source, the cloud and the Earth. Dark nebulae are also often seen in conjunction with reflection and emission nebulae. Diffuse and dark nebulae are typically tens of light-years across, and the largest are hundreds.
Supernova Remnants - Supernovae occur when a massive star ends its life in an amazing blaze of glory. For a few weeks a supernova can outshine its entire galaxy. When it's all over, a large fraction of the star is blown into space as a supernova remnant. Young remnants such as the Crab Nebula are about ten light-years across; older ones like the Veil Nebula have spread out to more than a hundred light-years.

Galaxies

There are hundreds of billions of galaxies, perhaps more, in the observable universe. Thousands are within reach of a medium to large telescope. Most look like faint, fuzzy patches. The Andromeda Galaxy is the nearest large galaxy to our own. It looks like a large, softly glowing oval in a telescope.

Messier Objects

Charles Messier was a comet hunter in the mid to late 1700s. You may be familiar with the pictures of comets that look like stars with long tails. This is what they look like when they are close to the sun. When they are still far from the Sun, they look like fuzzy patches in the telescope, like faint balls of cotton.

There are many objects in the sky that look similar to comets but are not. Messier could tell because they do not move relative to the stars. In order not to confuse these objects with a possible comet, Messier cataloged these fuzzy objects and gave them numbers.

As telescope technology improved, astronomers realized that these fuzzy objects were nebulae, star clusters, and galaxies. Today we use this catalog as a map of cool things to look at. There are 110 objects in the catalog. Many astronomy clubs have contests to see how many of the objects their members can find. In the spring they hold Messier Marathons, which are all-night observing sessions. Around March, from mid-northern latitudes, it is actually possible to view nearly all of the objects in one night.