On December 4, Mercury will reach its greatest eastern elongation, which is Mercury's last greatest elongation of the year. Astronomical science experts said that if the weather is fine, after the sun sets that day, interested members of the public can use binoculars or small astronomical telescopes to find Mercury at low altitude in the southwest.
Due to its proximity to the Sun, Mercury releases large amounts of sodium ions under solar wind radiation, creating an effect similar to that of a comet's tail. This is the "tail" of Mercury photographed by Pu Shi, a Beijing starry sky photography enthusiast, on October 3, 2022 using a high-magnification astronomical telescope and filters at the Ming Tombs in Beijing. (Photo courtesy of me).
Yang Jing, a member of the Chinese Astronomical Society and a director of the Tianjin Astronomical Society, said that Mercury is not easy to see because it is the closest planet to the Sun among the eight planets in the solar system. From Earth, Mercury is located near the Sun most of the time, rising and setting almost with the Sun, so it is often overwhelmed by the Sun's brilliance. It is only when the angular distance between Mercury and the Sun reaches its maximum, that is, the "great distance", because it is least affected by the sun's rays, and it is possible to see it at this time.
A close-up of Mercury taken by Liang Changhai, a starry sky photography enthusiast in Yunnan, in Huaihua, Hunan Province, March 30, 2023. (Photo courtesy of me).
Great elongation is a phenomenon unique to intraterrestrial planets such as Mercury and Venus. Around the time of the elongation, it is also a good time to see the planets in the earth.
Taking Mercury as an example, if Mercury is on the east side of the Sun, the maximum angular distance from the Sun is the greatest elongation to the east, and if it is on the west side of the Sun, the maximum angular distance from the Sun is the greatest elongation to the west. Because Mercury's orbit is relatively flat, the angular distance between Mercury and the Sun varies from 18 to 28 degrees at each great elongation.
A close-up of Mercury taken by Chen Suhui, a starry sky photography enthusiast in Jiangsu, in Nantong, Jiangsu Province, on November 9, 2020. (Photo courtesy of me).
At the time of the greatest eastern elongation, Mercury will appear low in the western sky in the evening and is called the "evening star";At great western elongation, Mercury appears low in the eastern sky at dawn and is called the "morning star."
Mercury orbits very fast, orbiting the Sun in just 88 days, so the eastern and western elongations occur three to four times a year.
A close-up of Mercury taken by Beijing star photography enthusiast Zhong Zhiqiang in Shunyi, Beijing, on October 24, 2021. (Photo courtesy of me).
Although Mercury's great elongation is not always suitable for observation during the year, it depends on how high Mercury's horizon is when the Sun is on the horizon. The higher Mercury horizon, the better the viewing conditions. Yang Jing said.
This year, Mercury has 6 major elongations, 3 each in its eastern and western elongations. During this great elongation, Mercury will shine at a magnitude of -04th class, the horizon height at sunset is about 11 degrees.
Tianjin starry sky photography enthusiast Wang Qiang photographed Mercury in the morning light in Tianjin on February 16, 2020. (Photo courtesy of me).
Observation of Mercury is not limited to the day of the greatest elongation. "A few days after this great elongation, Mercury's horizon elevation changed little and was still observable, and then it set rapidly, turning into a 'morning star' after the Lunar conjunction (i.e., Mercury between the Sun and the Earth) on December 23, and appeared low in the eastern sky before dawn. Yang Jing reminded.
Curator: Liu Xinhui.
Reporter: Zhou Runjian.
Editors: Chong Dahai, Zhu Shun.
Jointly produced by Xinhua News Agency and Xinhua News Agency Tianjin Branch.
Produced by Star Studios.