In April, as we step into spring, the celestial theater above us becomes lively once again. Events such as the Mars-Moon conjunction and the Lyrid meteor shower are highly anticipated. In this bright spring month, let us look up at the starry sky and experience the wonders above.
General Phenomena
01: Venus distance from Sun: 35.2^\circ W
04: 07:18 Saturn at Opposition
06: 23:06 Jupiter in Conjunction with Sun
07: 18:19 Moon-Pleiades Conjunction: 2.1^\circ N
10: 03:25 Mercury Inferior Conjunction
18: 06:04 Moon-Spica Conjunction: 2.5^\circ N
20: 02:12 Mercury-Mars Conjunction: 0.6^\circ N
23: 06:44 Lyrid Meteor Shower: ZHR = 20
Lunar Phases
03: 22:32 New Moon
11: 20:05 First Quarter
18: 10:44 Full Moon
25: 10:47 Last Quarter
April 4: Saturn at Opposition
The protagonist of the April sky is undoubtedly Saturn, accompanied by its beautiful rings. On April 4, Saturn reaches opposition. From Earth’s perspective, its ecliptic longitude differs from the Sun’s by exactly 180^\circ. This means that as the Sun sets, Saturn rises in the opposite direction, and it does not set until the Sun rises. For a long period around the opposition, we can observe it almost all night long.
Although Saturn is a favorite target for amateur astronomers, you might be slightly disappointed when you first see it through a telescope. In fact, Saturn’s opposition is not a particularly “spectacular” event; Saturn on this day will not look significantly different from usual. The main advantage of the opposition period is simply the longer duration available for observation.
During this opposition, Saturn is located in the constellation Virgo with a magnitude of approximately 0.3. The background of the sky features the famous Virgo Cluster of galaxies. If you use a camera for a long exposure of Saturn, you will find many distant galaxies distributed “around” it. Additionally, Saturn’s sixth moon, Titan, has a visual magnitude of 8.3, making it relatively easy to observe through a telescope.
April 23: Lyrid Meteor Shower
Compared to the traditional “big three” meteor showers, the Lyrid meteor shower has a smaller flow, but compared to many less active meteor groups, its flow is not insignificant. The active period of the Lyrids is from April 16 to 25 each year. Ancient Chinese records of meteor showers number about 180, of which about 9 refer to the Lyrids. The earliest record is in the Spring and Autumn Annals: “In the 7th year of Duke Zhuang of Lu, in the summer, in the 4th month, on the night of Xinmao, the fixed stars were invisible; at midnight, stars fell like rain.” The 7th year of Duke Zhuang corresponds to 687 BC, which is the world’s earliest record of the Lyrid meteor shower. While we cannot verify which specific star suddenly disappeared, the phrase “stars fell like rain” indicates that the Lyrid flow was once very large.
According to the International Meteor Organization (IMO) forecast, the peak of the 2011 Lyrid meteor shower is expected to occur between 23:30 on April 22 and 10:30 on April 23, Beijing Time. The peak flow is predicted to occur around 07:00 on the 23rd, with a theoretical Zenithal Hourly Rate (ZHR) of less than 18. Although it will already be daylight in most parts of China at that time, the Lyrid peak lasts for a relatively long duration, making the night of the 22nd to the early morning of the 23rd a good time for observation.
In 2011, most major meteor showers will be heavily disturbed by moonlight, and the Lyrids are no exception. The waning gibbous moon (21st day of the lunar month) will rise at midnight, significantly reducing the quality of the best observation window. The meteoroids of the Lyrid shower travel at a speed of 49 km/s and appear white. Since this period coincides with a season of few sporadic meteors in the Northern Hemisphere, distinguishing shower meteors from non-shower meteors is relatively simple, making it suitable for visual observation by beginner amateur astronomers.
Sun: At the beginning of the month, the Sun’s apparent Right Ascension and Declination are 00^h 40^m 09.485^s and +04^\circ 19' 19.362''; at the end of the month, they are 02^h 27^m 42.419^s and +14^\circ 35' 55.633''. This month, the Sun moves from Pisces to Aries. The solar term “Qingming” occurs on the 5th at 11:12, with the Sun’s ecliptic longitude at 15^\circ. “Guyu” occurs on the 20th at 18:17, with the Sun’s ecliptic longitude at 30^\circ.
Moon: The Moon passes through apogee, perigee, and aphelion at 17:00 on April 2, 14:00 on April 17, and 02:00 on April 30, respectively. The times for New Moon, First Quarter, Full Moon, and Last Quarter are April 3 at 22:32, April 11 at 20:05, April 18 at 10:44, and April 25 at 10:47, respectively.
Mercury: Mercury reaches inferior conjunction on April 10. Before the 10th, Mercury is an evening star, moving closer to the Sun. After the 10th, it becomes a morning star, and its distance from the Sun increases daily. It appears in the low northeast sky before sunrise and moves to the low southeast sky in late April. As the angular distance between Mercury and the Sun increases, its rising time advances, and its altitude at sunrise increases. However, because Mercury is close to the Sun in April, observation conditions are poor. On the 19th at 16:00, Mercury is in conjunction with Mars, with Mercury 0.8^\circ north of Mars.
Venus: A morning star. In April, Venus moves from Aquarius into Pisces. It is located in the southeast sky before sunrise. Its altitude at sunrise decreases from 14^\circ to about 12^\circ by the end of the month, with a brightness of about -3.9 magnitude. Due to its low altitude, it is not easy to observe. On the 23rd at 03:00, Venus is in conjunction with Uranus, with Venus 0.9^\circ south of Uranus.
Mars: In April, Mars moves prograde in Pisces. It rises in the east shortly before sunrise. At sunrise, it is located in the low southeast sky and moves to the low northeast sky in late April. Its brightness is about 1.2 magnitude, and its altitude is less than 10^\circ, making it difficult to observe. On the 4th at 02:00, Mars is in conjunction with Uranus, with Mars 0.2^\circ south of Uranus.
Jupiter: In April, Jupiter moves prograde in Pisces. It is close to the Sun and difficult to observe. On the 6th at 23:00, Jupiter is in conjunction with the Sun, completely lost in the Sun’s glare.
Saturn: In April, Saturn moves retrograde in Virgo and is visible almost all night. This is the best time of the year to observe Saturn. On the 4th at 08:00, Saturn reaches opposition, rising from the southeastern horizon after sunset with a brightness of about 0.4 magnitude. On the 17th at 16:00, Saturn is in conjunction with the Moon, with Saturn 8^\circ north of the Moon.
Uranus: Moving in Pisces. Close to the Sun, impossible to observe.
Neptune: Moving in Aquarius. Magnitude 8.0.
(Sources: “Astronomical Enthusiast”, NASA, Skylook, and other online resources.)
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