Mercury at Greatest Eastern Elongation

The best time to observe the innermost planet Mercury is coming. On Sunday, October 20, Mercury will reach its widest separation (25 degrees east) from the sun for the current apparition. The planet will be shining brightly at mag -0.1.

In astronomy, a planet's elongation is the angular separation between the Sun and the planet, with Earth as the reference point. Mercury is the smallest and innermost planet in the Solar System whose orbit lies closer to the Sun than the Earth's. This means that it always appears close to the Sun and is difficult to observe much of the time. The only time when the planet Mercury is well placed for observation comes a few days each time it reaches greatest elongation - greatest separation from the Sun.

With Mercury sitting below a shallowly dipping evening ecliptic in the west-southwestern sky, this will not be the most prominent appearance of the planet for Northern Hemisphere observers, but an excellent one for those at more southerly latitudes. The optimal viewing period for mid-northern latitudes falls between 6:45 and 7 pm EDT. Viewed in a telescope, Mercury will exhibit a waning gibbous phase. The planet will be positioned less than a fist’s diameter to the left (or celestial southeast) of bright Venus in the sky.

Star Walk 2 will help you identify the current position of Mercury and other celestial objects in the sky above you.

Clear skies and happy hunting!

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Image Credit:Vito Technology

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