Mercury can be seen in the eastern sky at dawn for a few days around greatest western elongation. It can also be seen in the western sky at dusk for a few days around greatest eastern elon gation. The...

Mercury can be seen in the eastern sky at dawn for a few days around greatest western elongation. It can also be seen in the western sky at dusk for a few days around greatest eastern elon gation. The following table shows the dates of the next few greatest elongations of Mercury. Magazines such as Sky & Telescope or Astronomy will tell you which, if any, of these greatest elongations is going to be especially favorable for viewing the planet. Alternatively you can use your Starry Night Enthusiast( planetarium software to examine these elongations. Open Sky Guide
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 A fast little world. This view shows Mercury and its orbital path around the Sun. Note how close Mercury stays to the Sun during its orbital journey. Stop the advance of time. Adjust the Date to each of the listed dates in the table below for Greatest western elongation and click on Sunrise to place the Sun on the horizon. You will note that the favorable elongations are those for which the angle of Mercury’s orbit with the horizon is largest. Why is Mercury at different altitudes (angles above the horizon) on different dates at these sunrise times? Now Adjust the Date to each of the listed dates for Greatest eastern elongation and click on Sunset and note the favorable dates for observing Mercury in the evening. Set the Time Flow Rate to 1 minute at any of these times and run time forward to observe Mercury’s descending motion with respect to the horizon.

If an elongation is favorable, make plans to observe this innermost planet of the solar system, a planet that is rarely seen by anyone but astronomers. Set aside several evenings (or mornings) around the date of the favorable elongation to reduce the chances of being “clouded out.” Select an observing site that has a clear, unobstructed view of the horizon where the Sun sets (or rises). Make arrangements to have a telescope at your disposal, if possible. Search for the planet on the dates you have selected and make a drawing of its appearance through your telescope.

*Mercury can be seen in the eastern sky at dawn for a few days around greatest western elongation. It can be seen in the western sky at dusk for a few days around greatest eastern elongation.