Mercury Orbit

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Cohdey

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Hi all,

I am new here, and joined in order to ask this question.

I read an article somewhere on the web a few months go about the planet Mercury being the closest to earth in its orbit in hundreds of years this August. I was wondering if I am remembering this correctly, or if I am having a brain drain. :D

The article said that Mercury won't be this close or this visible again for hundreds (or thousands maybe) of years. Am I remembering correctly? If this is really true, when is the best time and date to see Mercury?

Thanks for any help you can give me!!

Cohdey
 
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doubletruncation

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Hi Cohdey,

Mercury's closest approach to the Earth is actually the worst time to view it for two reasons: first, that is the point in its orbit when it will appear closest to the Sun on the sky and will therefore be very difficult to see, and second, at that point in its orbit we see the unlit side of mercury, so it is also faintest when it is closest to the Earth. Generally the best time to view mercury is when it reaches its maximum angle of elongation from the Sun (roughly when it is a quarter or three quarters of the way around the Sun with respect to the Earth). The maximum elongation will not be the time when Mercury appears to be the brightest, that will be when Mercury is on the far side of the Sun and we can see the full lit hemisphere, however at that time Mercury will also appear very close to the Sun on the sky, and will therefore be difficult to see. Using the JPL Horizon interface ( http://ssd.jpl.nasa.gov/horizons.cgi ) it looks like you can see Mercury now just after sunset, and it will reach a maximum elongation from the Sun of ~27 degrees on ~ August 25, 2009. On average the time between maximum elongations is ~58 days, with the maximum elongations alternating between being best viewed in the morning and best viewed in the evening. The maximum possible elongation is ~28 degrees, and it comes pretty close to this on a fairly regular basis. Realistically you wouldn't notice a big difference between the maximum elongation on August 25 of ~27 degrees and the maximum possible elongation.
 
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MeteorWayne

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Cohdey,
You are probably confusing Mercury with Mars, and heard about the great Mars "hoax". Every year since the closest approach between the earth and Mars in 2003, the same story circulates on "Teh Interwebz" with the story getting more and more distorted every year.

To read more about it, see this:

http://www.skyandtelescope.com/news/8708182.html
 
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