The spring-like April sky "theater" also began to "warm up"

Tianxiang knew

Li Xin

Entering April, China is surrounded by spring. As the weather warmed up, the celestial "theater" gradually became lively. In this month, the protagonist is still a few visible planets. In late April, the Lyra meteor shower will usher in a great deal. And two non-periodic comets will also enter our field of vision.

At the end of the moon, Venus shines brightly among the stars

Venus is the "star" of the canopy we are already familiar with. The bright light spot in the western sky in the evening is Venus. Some people may ask, isn't Venus called "Revelation Star" and appeared in the East before sunrise? In fact, as an inner planet, Venus will appear on both sides of the sun. When it appears on the east side of the Sun, it is visible at dusk, and Venus at this time is also called "Chang Geng Star".

In 2020, in the first few months, Venus was "Chang Geng", and its brightness gradually increased. After entering April, although the ground level at sunset has decreased, the brightness has not decreased. On April 28, Venus reached the brightest time this time it appeared on the east side of the Sun, with a magnitude of -4.7, which is almost 100 times that of Vega. On April 26, Venus will also coincide with the moth moon of the fourth day to stage Venus with the moon.

Except for Venus, the three extraterrestrial planets of Mars, Jupiter, and Saturn are mainly visible in the second half of the night. You may remember that in late March they had a "Samsung Convergence" with a close angular distance. Mars will gradually "away" from Jupiter and Saturn in April, but the angular distance between the latter two will become smaller and smaller. From April 15th to 16th, the second quarter of the moon will stage a "Samsung Moon" with three planets.

Lyra meteor shower is extremely long

Lyra meteor shower is a relatively rare meteor shower active in spring in the northern hemisphere. Human observation of the meteor shower in Lyra has a long history. The earliest observation records of Lyra meteor shower in China can be traced back to the Spring and Autumn Period more than 2,600 years ago. This shows that the meteor shower has experienced a burst of heavy traffic. However, in recent years, the meteor shower in Lyra has been quiet. Even on the great night, its traffic is only a dozen or so per hour, and we can only see one meteor in the group about every 10 minutes.

The active period of the Lyra meteor shower is from April 14th to 30th every year, and this year's extreme is expected to appear on the afternoon of April 22th, Beijing time. The maximum duration of the meteor shower in Lyra is relatively long. The average time for the flow to remain above half of the peak is 32 hours, and the longest time can reach 61 hours. So we only need to remember its huge date, the specific time is not so important. For this year, the two nights from the evening of April 21 to the early hours of 23 are more suitable for observation. And the 23rd coincides with the "Shuo" of the lunar calendar. Moonless nights will provide good conditions for observation.

"Rising star" comet Y4 is more worthy of attention

There are currently two comets in the night sky that deserve attention. They are all non-periodic comets, numbered 2017 T2 (PanSTARRS) and 2019 Y4 (ATLAS), which we refer to as T2 and Y4, respectively. Both comets will pass the perihelion in May. At the beginning of the year, people had very high expectations for comet T2 and expected it to reach the brightness visible to the naked eye in April. But now it seems that this comet may disappoint everyone. Although its observation conditions have been good, it can be seen almost all night in the northern and middle latitudes. However, as of late March, its brightness has stagnated at the 9th level, and I am afraid that it can only be at the 7th level at its brightest.

Another comet, Y4, can be described as a "rising star" this year, and it is now being sizzled. This comet was only observed at the end of last year, and its brightness has increased rapidly, reaching about 8th grade in late March. With regard to its brightness prediction during the perihelion, there is a large gap. The very optimistic situation is that it can reach -10, which is the level of the moon. Some "pessimistic" estimates can also reach 4 to 5 visible to the naked eye. The declination of Comet Y4 before the perihelion is also very high. It is very suitable for the northern hemisphere from April to early May. The brightness at that time is naturally the best if it can reach the level visible to the naked eye. However, when it passed the perihelion at the end of May, its distance from the sun was only 0.25 astronomical units. The observation angle distance on the earth is very small, even if it is bright, it is difficult to be observed.

The comet's nucleus is currently in a process of change and may partially disintegrate. But for a comet that is about to pass through the perihelion, this is also a normal phenomenon. At present, it seems that the brightness uncertainty that it can achieve in May is very high. I suggest you pay attention.

(The author is an associate researcher at the Beijing Planetarium)