Mercury and Venus are regularly at their greatest elongation. It is a very good period to observe these planets in the sky. But what does that mean, exactly?
Little Mercury is at its maximum elongation: the planet is moving 26.3° away from the Sun this Wednesday, February 16, 2022 (at 10:06 p.m. very precisely). This means that right now Mercury can be seen well in the sky. You should try to observe it in the morning, because it is a West elongation.
But what exactly happens in the solar system, when we speak of maximum elongation for certain planets? This configuration only exists for the so-called “inferior” planets, that is to say, the orbit around the Sun is smaller than that of the Earth. This is therefore only possible for Mercury and Venus. Mars, Jupiter, Saturn, Uranus and Neptune are so-called “superior” planets.
As the Institute of Celestial Mechanics and Ephemeris Calculation (IMCCE) explains, the maximum elongation is “ the configuration for which the apparent angular distance of the planet and the Sun is the greatest “. The following animation, created by Numerama, helps to better understand this definition.
Elongation, opposition: what difference in astronomy?
Unlike the superior planets, the inferior planets cannot be at the opposition: this occurs when a planet, seen from Earth, is opposite the Sun in the sky. This is a very good time to see these planets, which are almost visible all night at this time. ” For the higher planets of the solar system, the maximum elongation corresponds to the opposition, that is to say to an elongation of 180° “, completes the IMCCE.
As this 180° configuration is not possible with the lower planets, it is the moment of their maximum elongation which is most favorable for their observation: between 18 and 28° for Mercury, between 45 and 47° for Venus. ” When Mercury and Venus are near their ‘greatest eastern elongation’, they are visible after sunset. Conversely, when they are close to their ‘greatest western elongation’, they are visible before sunrise. “, specifies the IMCCE.
The advantage of Mercury and Venus is that they are planets visible to the naked eye. Even if you don’t have an instrument (sunglass, telescope), you can find them with your eyes — if the weather conditions are good, of course.
Mercury’s next maximum elongation is scheduled for April 29, 2022, at a distance of 20.6° from the Sun. It will be a greater East elongation, so Mercury will be visible in the evening.