Catch The Elusive Planet Mercury After Sunset

In early June 2020, skywatchers in some parts of the world will have the opportunity to see the elusive planet Mercury with the naked eye after sundown. Read on to find out how, when and where to spot the smallest planet of the Solar system.  

How and where to see Mercury

  Mercury will reach its greatest eastern elongation (greatest separation from the Sun) on Thursday, June 4, 2020, but will be easy to spot in the sky on the evenings of both June 3 and 4. At its greatest elongation, the planet will be 24 degrees east of the Sun. Observers will be able to see Mercury with the naked eye around 40-60 minutes after sunset. The innermost planet will shine at magnitude 0.4. It will rise not very high above the western horizon and will be located between two bright stars – Capella and Procyon.   For better results, choose your observing location with an unobstructed view in the direction of sunset. The stargazing app Star Walk 2 will help you determine the best viewing time for your area and will show you where to look in the sky to find Mercury. If you want to take a look at the planet's disk, use a small telescope. Through a telescope, Mercury will appear as a waning, less than half-illuminated disk (about 40% illuminated).  

Who will see the elusive planet?

  This evening apparition of Mercury will favor the Northern Hemisphere observers. For skywatchers in the Southern Hemisphere, viewing conditions will be poor. It is difficult to view the planet in the Sun's glare most of the time. If you live in the Northern Hemisphere, use the opportunity to spot Mercury on June 3-4, 2020, as the planet will become fainter in the evening sky with each passing day.  

What is elongation?

In astronomy, a planet's elongation is the angular separation between the Sun and the planet, with Earth as the reference point. In other words, elongation is the angle between the Sun and the planet, as seen by an observer from Earth.

The greatest elongation is possible for the two inferior planets – Mercury and Venus, as they are closer to the Sun than the Earth and never stray too far from it in the sky. The maximum elongation angle of the Sun for Mercury is 28 degrees, for Venus – 48 degrees.

At and near its greatest elongation, a planet is very well placed for observation. When a planet reaches greatest elongation (or greatest separation from the Sun), it appears farthest from the Sun as viewed from Earth and can be easily identified in the sky even without optical aid.

Eastern and western elongation

A planet can be at an eastern or western elongation. Since Mercury and Venus are always located near the Sun, we can only observe them in the evening or morning sky and never in the middle of the night.

Mercury and Venus are observable in the evening sky when they are to the left (or east) of the Sun. Thus, evening elongations are called eastern. During eastern elongation, a planet rises and sets shortly after the Sun.

Morning elongations are called western. During morning elongations, Mercury and Venus are located to the right (or west) of the Sun. The planets rise and set a short time before the Sun and are visible before sunrise.