24 February 2008

How to see Mercury

I've been asked in the past how to find Mercury. Because it is so close to the Sun compared to any other planet in the Solar System, it is harder to spot than the rest and never appears very far away from the Sun (that is, it never appears high up in the night sky). However, because it is relatively close to Earth, it can also become quite bright. These two factors combine to make Mercury a challenge to see but still a fun goal for many. The coming weeks offer an opportunity to try to see it.

Mercury and Venus are both circling the Sun inside the orbit of Earth and both move faster than Earth. In a single 12 month period of time, Mercury will circle the Sun over 4 times. As it speeds on its orbit, it is visible low on the horizon in the evening or morning sky. Right now both Mercury and Venus are very low on the horizon in the morning and if you have a clear view and good timing, you can see the two dance along the horizon. The diagram shows where to look for them.

In 2004 NASA launched the Messenger spacecraft to explore Mercury and in January 2008 it finally made its first pass, flying just over 100 miles above the surface of Mercury. Messenger is returning some amazing photographs of the planet. To my surprise, Mercury looks exceedingly similar to our own Moon. For pictures, visit http://www.nasa.gov/mission_pages/messenger/main/index.html.

Mercury and our Moon have much in common, being of similar age, made of similar minerals, and both having no atmosphere*, they are bombarded by meteors and have no erosion or surface flows which change its appearance over time. Hence they both appear similar on their surfaces. For me, seeing the photos reminds me that there are lots of things we share in common with our neighbors in space and by exploring our own Solar System we can better understand what is happening in other star systems and galaxies.

* Note: Mercury has an extremely thin atmosphere due to the solar wind lifting particles off the surface of the planet, but this layer of atoms is being constantly "burned off" and is not a permanent atmosphere as we have on Venus, Earth or Mars.

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