Mercury’s eastern elongation is also called the evening one because the planet is best observed during the evening hours. The number varies because Mercury’s orbit is slightly tilted and is not perfectly circular. The maximum elongation angle for Mercury is between 18° and 28° east or west of the Sun. When Mercury is positioned to the east of the Sun, it’s an eastern elongation, and when it’s to the Sun’s western side, it’s a western elongation. There are two types of elongations – eastern and western. Elongations occur every 40-70 days and are a delight for any astronomy lover. Astronomers call this event “the greatest elongation”. The most favorable time for observation of Mercury is when the planet reaches its greatest separation from the Sun, as seen from the Earth. However, at certain periods of time, the elusive planet becomes visible for us. That’s why many people have never seen Mercury. The answer is simple: Mercury is the closest planet to the Sun and, most of the time, it is obscured by the Sun’s glare. Although Mercury is small, it’s quite bright to be observed with the naked eye, so why can’t we see it? Even people, who are not interested in astronomy, can accidentally spot Venus, Mars, or Jupiter shining in the sky, but never Mercury. Mercury is often called the “elusive planet”.

In today’s article, we’ll tell you more about this event and give you tips on how to spot the planet with your own eyes. On January 23, Mercury will reach its greatest eastern elongation and shine bright in the evening sky.

Moon elongation angle