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Challenge #1 – Seeing Mercury at Greatest Elongation

Mercury Statistics

TargetTypeRight Ascension*Declination*ConstellationMagnitudeSize
MercuryPlanet22h 43m 03s-07° 20′ 24″Aquarius-0.57.1 arcseconds

*At moment of greatest elongation on Feb 10th. See ‘planets’ section for daily guides to the planet’s position.


Where to Find Mercury

Mercury is the closest planet to the sun and moves around it swiftly. It takes just 88 days for Mercury to complete a full orbit of the sun meaning that we get to see it approximately six times a year, three in the morning and three in the evening.

Because it is so close to the sun, we only ever see it in the twilight glow after sunset or before sunrise. The planet never ventures far away enough from the sun for us to see it in darkness. However, at moments of greatest elongation, it is as far from the sun as it gets, making these the ideal time to point our telescope in its direction. On the evening of February 10, Mercury reaches one of these greatest elongations.

The picture below from SkySafari 6 shows you where to find Mercury 45 minutes after the sun has set that day. Click the image to open a full screen version.

Look low above the western horizon, below the dazzlingly bright Venus. Mercury is about 10° above the horizon at this time for mid-latitudes of the US, the further north you are, the lower in the sky Mercury will appear. Conversely, the further south you live, the higher Mercury will be in your sky.

Through a telescope on higher magnification, you’ll see a crescent shape which is only 50% illuminated; it will appear as a very small version of our first quarter moon.

Sadly, there are no moons around the little planet for us to spy, nor are there surface features we can try to bring out. But, seeing this tiny, illusive planet is achievement enough in its own right. Good luck!