Observing Project 8A The Rotation of Mars

Mars rotates on its axis just like Earth does and in almost the same amount of time. The planet's sidereal period is only 41 minutes longer than Earth's is. This is one of the easiest things to gauge about the planet because its surface markings are consistent and easy to see. You can study the rotation of Mars in one of two ways.

If you want to spend a few hours at the telescope you can watch the planet's features slide across its disk. Pick an object near the planet's central meridian and time how long it takes for it to reach the planet's limb. In just a bit over six hours your point should roll out of sight and into Martian night.

A simpler way to do the same thing would be to watch the planet on a successive series of nights. Since Mars takes about forty minutes longer to complete a rotation than Earth does, each night a feature on the planet's central meridian will retreat a bit further onto the planet's morning hemisphere each day. Over the course of about a month, you can track the planet through an entire reverse rotation in this way. Pick a prominent feature like Hellas or Sinus Sabaeus and track it from night to night. This drill will also help you begin to grow familiar with the geography of Mars.

When working with Mars use all the power the seeing will tolerate. Also use filters. To enhance surface features you should use red and orange filters. These block light from haze and clouds and increase contrast among surface features. Study your maps and know the planet's features and geography and you can recreate one of the most important early discoveries about Mars in the telescopic era.

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