Mercury will move to its greatest western elongation on May 10. Astronomical science experts said that during this great elongation, the horizon altitude of Mercury is very low, and it is difficult to observe, but it is also a rare opportunity for astronomy enthusiasts who dare to challenge.
Relative to the position of the Earth, the planets in the solar system can be divided into two categories, one is an intraterrestrial planet and the other is an extraterrestrial planet. Intraterrestrial planets refer to Mercury and Venus orbiting within the Earth's orbit, and from Earth, they always oscillate back and forth near the Sun, no more than a certain angle at most. In the case of Mercury, this angle will not exceed 28 degrees.
Yang Jing, a member of the Chinese Astronomical Society and a director of the Tianjin Astronomical Society, said that if you want to see Mercury's "true face", you must wait until its angular distance from the sun reaches its maximum, that is, the farthest position of Mercury from the sun from the earth. If Mercury appears in the east of the Sun, it is called the eastern elongation, when Mercury appears low in the western sky at dusk; If Mercury appears to the west of the Sun, it is called the greatest western elongation, when Mercury appears low in the eastern sky at dawn. There are usually 6 to 7 great elongations of Mercury each year, including the eastern and western elongations.
The length of time Mercury rises above the eastern horizon before the Sun at the western elongation is not exactly the same, sometimes earlier and sometimes later, resulting in mixed viewing conditions. The earlier the sun rises, the darker the sky background will be, and the more likely Mercury will be observed.
"This is the second time that Mercury will have four western elongations this year, and although Mercury can reach a magnitude of 0.5, it is the most unfriendly observation conditions. This is because, although Mercury rises above the ground before the Sun, the sky is already brightening when it rises, and the observable time is very short; Although the angular distance between Mercury and the Sun reaches 26 degrees, the horizon height of Mercury at sunrise is only 10 degrees, which is very low, and it is easily affected by the low-altitude atmosphere and obscured by buildings and trees on the ground. Yang Jing said.
Observation of Mercury is not limited to the day of the greatest western elongation, but can be observed within a week, but it needs to be sunny and transparent, and avoid the obstruction of buildings and trees on the ground.
"Observations can begin more than 1 hour before sunrise and end nearly half an hour before sunrise. It is best to use a small astronomical telescope or a large-aperture binocular, and the success rate will be greatly improved. Yang Jing reminded.
Editor: Chen Ruizhi
Source: Xinhua News Agency