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Astronomy Hints #5: Viewing the Inner Planets

We’ve covered the easiest telescope target in a previous post on viewing the Moon and now it is time to start thinking about using your telescope to view other members of our solar system – the planets. We’ll start with actually can be a harder target in some ways: The inner planets, or at least the ones closer to us. This means Mercury, Venus, & Mars.

Most of the planets are bright enough that they are not affected by light pollution much. Viewing them is subject to other atmospheric conditions, however.

Mercury – Right off the bat we should let you know that Mercury is a very tough object to view. Being the closest planet to the sun means that most of the time it gets washed out by sunlight. However, every now and then Mercury reaches its furthest orbital distance from the the sun and sticks out far enough so that right after the sun sets Mercury can be seen.  This is the best time, in fact the only time to view Mercury (although it can also be viewed when the same orbital conditions happen during a sunrise). Don’t expect very much, Mercury will appear to be little more than a dot in your telescope.  Most astronomers usually hunt down Mercury just to say that they have done it rather than for any impressive views.

Venus –  Venus is also closer to the sun than the Earth, which means it will only be visible right before the sun rises or right after the sun sets. Hence Venus’ other names “Morning Star” and “Evening Star”.  Venus will usually be very bright and easy to find when it is up. When magnified in your telescope Venus will likely have a crescent shape visible much like the Moon but probably won’t have many surface features, at least without a filter. This is because of Venus’ heavy cloud cover. That same cloud cover makes it very reflective and bright but removes any surface detail.

Note than on some occasions, with a bit of experience you can actually view Venus in the middle of the day! This takes some practice to do, however.  It is one of the occasions where a computer-aided telescope can actually help quite a bit.

Mars – Mars is the first planet that is actually further from the Sun than Earth. It is reddish in appearance -even without a telescope. When it is up you can try to crank up the magnification. Most of the time Mars is a decent object to view, but about every 24-25 months Mars reaches opposition, where it is closest to Earth. This is best time to view Mars and with decent skies, a good telescope, and high magnification you might be able to get details such as the polar caps! As of this writing the next opposition will be in March of 2012.

A note about Mars – Every time Mars comes into opposition some folks send out emails with ludicrous claims about  how Mars appear as big as the Moon in the sky. These emails are recycled from the 2003 opposition which was the closest opposition in some 50,000 years. But even during that opposition Mars certainly did not appear as big as claimed. When you get these emails, please do not forward them.

Asteroids and Minor Planets – These can be tricky targets and often require a bit of detail and knowledge of the sky to find them. They also require a good quality telescope to locate. Get some experience working with the night sky before you start hunting asteroids.

A Note About Filters:The brighter planets are often bright enough

Color Filters

Colr Fitler Set

that you can consider using color filters that thread onto your telescope’s eyepiece. These filters can help bring out surface details that would otherwise not be viewable in normal conditions. A Red #25 filter, for example, can bring out cloud detail on Venus. Trying different filters can bring a new experience to your viewing of the planets.

In our next Astronomy Hints we will tackle the bigger denizens of our Solar System (well, most of them are bigger anyway)- The outer planets!