The April celestial "theater" is also beginning to "warm up" with the spring in the air

The radiant point during the Lyrid meteor shower peak. Photo courtesy of the author

As April begins, spring is in the air across China. As the weather warms up, the astronomical "theater" is gradually becoming more lively. This month, the main stars are still several planets visible to the naked eye. In late April, the Lyrid meteor shower will reach its peak. And two non-periodic comets will also enter our field of vision.

Venus outshines all other stars at the end of the month

Venus is a familiar "star" in the sky. The bright spot of light in the western sky in the evening is Venus. Some people may ask, isn't Venus also called the "morning star" and appears 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 is also called the "Everlasting Star".

In 2020, Venus was a "long-lived star" in the first few months, and its brightness gradually increased. After entering April, although its altitude at sunset decreased, its brightness did not decrease. On April 28, Venus reached its brightest appearance on the east side of the sun, with an apparent magnitude of -4.7, almost 100 times that of Vega, and it was the most dazzling star. On April 26, Venus will also be in conjunction with the crescent moon on the fourth day of the first lunar month, presenting the phenomenon of Venus accompanying the moon.

In addition to Venus, the three extraterrestrial planets Mars, Jupiter and Saturn are mainly visible in the second half of the night. You may remember that in late March, they had a "three-way conjunction" with a very close angular distance. In April, Mars will gradually "move away" from Jupiter and Saturn, but the angular distance between the latter two will become smaller and smaller. From April 15 to 16, the last quarter moon will perform a "three-way conjunction" with the three planets in this area of ​​the sky.

The Lyrid meteor shower will have a long peak period

The Lyrid meteor shower is a relatively rare meteor shower active in the spring of the Northern Hemisphere. Humans have been observing the Lyrid meteor shower for a long time. The earliest observation record of the Lyrid meteor shower in my country can be traced back to the Spring and Autumn Period more than 2,600 years ago. This shows that the meteor shower once had a large flow rate. However, in recent years, the Lyrid meteor shower has been somewhat quiet. Even on the night of the maximum, its flow rate is only a dozen per hour, and we can only see one meteor in the group about every 10 minutes.

The Lyrid meteor shower is active from April 14 to 30 every year, and this year's peak is expected to occur on the afternoon of April 22, Beijing time. The Lyrid meteor shower peak lasts for a long time, with the flow rate remaining more than half of the peak for an average of 32 hours, and up to 61 hours. Therefore, we only need to remember the date of its peak, and the specific time is not so important. For this year, the two nights between the evening of April 21 and the early morning of April 23 are more suitable for observation. In addition, the 23rd is the "new moon" of the lunar calendar, and the moonless night will provide good conditions for observation.

Comet Y4 is a rising star worth paying more attention to

There are two comets in the night sky that are worth paying attention to. They are both non-periodic comets, numbered 2017 T2 (PanSTARRS) and 2019 Y4 (ATLAS), which we refer to as T2 and Y4 respectively. Both comets will pass perihelion in May. At the beginning of the year, people had great expectations for Comet T2, and expected it to reach a 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 middle and high latitudes of the northern hemisphere. But as of late March, its brightness has stagnated at 9th magnitude, and I am afraid that it can only be around 7th magnitude at its brightest.

Another comet, Y4, is a rising star this year and is now very popular. This comet was only observed at the end of last year, and its brightness has increased rapidly. In late March, it has reached about magnitude 8. There is a large difference in the forecast of its brightness during perihelion. The most optimistic scenario is that it can reach -10 magnitude, which is the level of the moon. The more "pessimistic" estimate is that it can reach magnitude 4 to 5, which is visible to the naked eye. Comet Y4 has a high declination before perihelion, and the entire April to early May is very suitable for observation in the northern hemisphere. It would be best if the brightness can reach the level visible to the naked eye. But when it passes the perihelion at the end of May, its distance from the sun is only 0.25 astronomical units, and the observation angle distance on the earth is very small. Even if it is relatively bright, it is difficult to observe.

The comet's nucleus is currently in a process of change and may partially disintegrate. But this is normal for a comet that is about to pass perihelion. At present, the brightness it can reach in May is highly uncertain, so please pay attention.

(The author is Li Xin, associate researcher at the Beijing Planetarium)