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Stargazing conditions are improving. In September, watch these planets “sing leadership”
Heaven has known
Li Xin
The rainy season is gradually coming out of various locations in September, and conditions for stargazing are getting better and better. The star in the night sky this month is still the planet. Among the planets visible to the naked eye, only Mercury is difficult to find. Neptune will oppose the sun this month, but it is too far and too dark, and you must use a telescope to see it. The ε Perseid meteor shower in September will also usher in much, but this time the appreciation effect will be greatly reduced under quarter-moon interference.
Mars will start “retrograde” after the moon
Best time to watch: September 6
Recommendation index: ★★★ ☆☆
Observation Difficulty: ★★ ☆☆☆
Among the extraterrestrial planets, Mars has the least chance of being visible. It is best suited for observing only a few months every two years. The rest of the time it is relatively dark and the distance to the sun is relatively close. After the big collision in July 2018, Mars re-entered our field of view this summer. October 14 will mark the beginning of an opposite sun relatively close to Earth, with a brightness of -2.6 and so on.
Mars’ departure time this month has been brought forward to around 7pm and the brightness has risen further. At noon on September 6 Beijing time, Mars will join the waning gibbous moon. That night, we can see it rise together with the moon at an angular distance of only about 4 °. Right now, Mars, whose brightness is close to -2, is very striking, and the encounter with the moon will make it appear a bit dark. . On September 10, Mars will change from prograde to retrograde. At this moment, it appears to be motionless in relation to the starry sky in the background. This moment of the planet is called “stay”.
The celestial phenomena related to the moon in September and the conjunction of Venus and the waning moon on September 14. On the night of September 25, the quarter moon will approach Jupiter and Saturn, and a double star with a moon will appear.
Meteor “light rain” under Perseus
Best time to watch: September 9
Recommendation index: ★★ ☆☆☆
Observation Difficulty: ★★★ ☆☆
Because the radiant point is also in the Perseid sky area, the September ε Perseid meteor shower is easy to leave a deep impression on people, but in fact its flux is not at the same level as the huge Perseid meteor shower in August. The active period of this meteor shower is from September 5 to 21 of each year, due to the high declination of the radiant point, it is very suitable for observation in the northern hemisphere. In existing observational records, there have been small-scale outbreaks in 2008 and 2013, with an hourly flow of about 30. However, through analysis of the current orbit model, it will be difficult for you to have activities of this scale in the next 30 years, and the annual flow at peak time is likely to be in just single digits.
Around 10 p.m. on September 9, the radiant point of the ε Perseid meteor shower in September will rise to a height well suited for observation, and can be observed during the second half of the night until dawn. However, the extreme period of this year coincides with the upper and lower quarter moon, and the moon will rise at midnight. The few original meteors in the group are even more difficult to observe under moonlight. However, occasional meteors appear more frequently in the latter half of autumn in the Northern Hemisphere. Moonless nights around September 17 are well suited for stargazing while observing meteors.
The “planets on the tip” are visible all night
Best time to watch: September 12
Recommendation index: ★★ ☆☆☆
Observation Difficulty: ★★★★ ☆
Neptune is the third most massive planet and the fourth most massive in the solar system, and its radius is 3.9 times that of Earth. Because it is so far away from the earth and the sun, its apparent magnitude is only 7.7 and we cannot observe Neptune with the naked eye. Although it was one of the important members of the solar system, it was very difficult for people to observe and calculate the orbit of such a planet 200 years ago. In 1846, Le Vieux of France and Adams of England respectively calculated another possible planet through the orbit of Uranus. Subsequently, Galler of the Berlin Observatory in Germany observed Neptune in an area of 1 ° near the position calculated by Le Vier. Therefore, the planet whose orbit is calculated before being confirmed by observation is called the “planet at the tip of the pencil.” The English name “Neptune” for Neptune comes from the god of the sea in Roman mythology. Later, when the Voyager 2 probe flew over Neptune, it observed its dark and complicated halo, so people named the three main rings after Levier, Adams, and Galle.
Neptune’s period of revolution is 164.8 years, which means that it moves very slowly in the night sky. On September 12, it will be located in the Aquarium zone during the opposition and will be visible all night. The observation of Neptune is inseparable from an astronomical telescope. On the lens of a small telescope, Neptune is just a small faint blue dot, which is difficult to distinguish from a star. Only the Voyager 2 probe passed Neptune in 1989. In addition to detecting its halo, satellites, and atmospheric composition, humans still know very little about Neptune. As more and more Neptune-like exoplanets are discovered, the structure and origin of this distant planet have sparked great interest among astronomers, and humanity is also preparing a “return to Neptune” plan.
(The author is a research associate at the Beijing Planetarium)
