August, at the turn of summer and autumn, the celestial theater remains brilliant and diverse. Among the highlights, the Perseid meteor shower is the most anticipated, being the project amateur astronomers are most passionate about observing every year. Although the observation conditions for several bright planets are relatively average this month, Neptune will be at opposition on August 23, and interested friends can use telescopes to observe it. Additionally, the well-known Comet 45P/Honda-Mrkos-Pajdusakovva will pass perigee on August 16, gradually entering a better observation period.
Astronomical Overview
01st 19:20 Mercury-Moon Conjunction: 1.5^\circ N
05th 11:08 Moon-Spica Conjunction: 2.5^\circ N
07th Vesta at Opposition
13th 13:41 Perseid Meteor Shower: ZHR = 90
16th 19:41 Venus Superior Conjunction
17th 08:56 Mercury Inferior Conjunction
22nd 07:40 Moon-Pleiades Conjunction: 2.5^\circ N
23rd 05:46 Neptune at Opposition
25th 21:36 Moon-Mars Conjunction: 2.8^\circ N
Lunar Dynamics
06th 19:08 First Quarter
14th 02:57 Full Moon
22nd 05:55 Last Quarter
29th 11:04 New Moon
August 7: Vesta at Opposition
Vesta is the fourth asteroid discovered by humans and the second largest asteroid in volume, second only to Ceres. When the German astronomer Heinrich Wilhelm Olbers discovered it on March 29, 1807, he named it Vesta, after the Roman goddess of the hearth and temple. When Vesta is closest to Earth, it is only 220 million kilometers away. Therefore, although it is not large, its brightness usually stays around magnitude 7, and it can reach magnitude 5.7 at opposition. Although this brightness is higher than the limit of the human eye under good observation conditions, we still need the help of a telescope to find it among the stars. During the opposition on August 7, 2011, Vesta is located in the constellation Capricornus. I have provided the star chart below to help everyone find it. It should be noted that Vesta’s proper motion is very fast; this star chart is applicable for a range of approximately one day. If you wish to observe it at other times, you will need to check an electronic star chart yourself.
August 13: Perseid Meteor Shower Peak
As one of the three major meteor showers in the Northern Hemisphere, the Perseid meteor shower has a large and stable flow, possessing both scientific research significance and great ornamental value. Both astronomers and ordinary enthusiasts are fond of it. The active period of the Perseids is from mid-July to late August every year, almost covering the entire summer vacation for students, which allows more student enthusiasts to participate in observation activities.
Meteor showers are usually related to comets. When close to the Sun, a comet is affected by its massive gravity and radiation, ejecting a large amount of dust material. Part of this dust material remains near the orbit, forming a columnar dust belt. When the Earth orbits the Sun and passes through this dust belt, a meteor shower occurs. The comet that brings us this meteor shower is called the parent comet; the parent comet of the Perseids is Comet 109P/Swift-Tuttle. If the Earth happens to pass through a denser area of dust, the flow of the meteor shower will be larger. We usually use the Zenithal Hourly Rate (ZHR), which assumes the radiant point is at the zenith, to represent the size of the meteor shower flow. The ZHR of the Perseids is around 120, and in recent years, it has even reached above 150. Under normal circumstances, it is one of the meteor showers with the largest flow.
According to the forecast of the International Meteor Organization, the peak of this year’s Perseids may occur at 14:00 Beijing time on August 13. Since it will be daytime, China will not be able to observe it during this period. However, the peak duration of the Perseids is long, and multiple flow peaks may occur. Enthusiasts in China should observe it from the night of the 13th to the dawn of the 14th. The radiant point of the Perseids is located between the constellations Perseus, Camelopardalis, and Cassiopeia, with a declination of +40^\circ. Therefore, for a 50^\circ N latitude region, the radiant point will be close to the zenith when it culminates, and the number of meteors observed at this time will be closest to the theoretical value. However, in mid-August, the sky becomes bright before the radiant point culminates. Thus, the best time for this meteor shower is in the second half of the night before the beginning of astronomical twilight. However, this year’s peak date coincides with the 14th day of the lunar month, and the full moon will bring serious light pollution, which will discount the observation effect of the meteor shower to some extent. Photographic observation is most affected by moonlight; if a long exposure time is used, some fainter meteors will be drowned out by the background sky light. Visual observation is relatively less affected, and interested friends can still give it a try.
The meteors within the Perseid shower move quickly, at 59 km/s, and appear blue-green. There are many bright meteors, making them easy to distinguish from meteors of other showers.
August 16: Comet 45P/Honda-Mrkos-Pajdusakovva at Perigee
The orbital period of Comet 45P/Honda-Mrkos-Pajdusakovva is 5.25 years, and it is one of the brighter comets returning this year. On September 28, the comet will pass perihelion. When it passes perigee on August 16, it will be only 0.06 astronomical units away from us, which is about 9 million kilometers. Although its brightness is expected to reach above magnitude 7 during this time, its declination is low. Observation conditions in the Southern Hemisphere are acceptable, but astronomical enthusiasts in China will not be able to observe it. However, there is no need to worry; after mid-September, we may be able to observe it in the low eastern sky before sunrise. At that time, as it gradually approaches the Sun, its brightness will also maintain a high level.
Usually, comets are named after their discoverers, so I have had a sense of respect for the name of every comet since I was a child. Japan is a country that produces many comet hunters. Many amateur astronomers are passionate about searching for comets, and their level is very high, with frequent discoveries. For example, 45P was discovered by the late famous Japanese comet hunter Minoru Honda, and others like Kaoru Ikeya, Tsutomu Seki, and Yuji Hyakutake are also very famous. Although searching for comets is difficult, the threshold for many amateur astronomical observation projects is actually not high for enthusiasts. I hope that Chinese astronomical enthusiasts can learn more from their counterparts in neighboring countries, work hard to improve their observation levels, and understand more astronomical knowledge through practice.
August 23: Neptune at Opposition
Among the eight classic planets of the solar system, the last one discovered by humans, Neptune, will be at opposition on August 23. Due to its distance of about 4.4 billion kilometers from Earth, the apparent disk of Neptune at opposition will be very small and very faint, no different from usual. Therefore, it is clearly inappropriate to use words like "brilliant" or "spectacular" to describe the Neptune opposition phenomenon.
The brightness of Neptune at opposition this year is about magnitude 7.8, located in the constellation Aquarius. You still need to use a telescope to find it. Of course, if you want to observe its apparent disk or capture its beautiful deep blue color, you will need to use a larger aperture telescope.
Solar System Dynamics
Sun
At the beginning of the month, the Sun’s apparent RA and Dec are 08^h 43^m 25.781^s and +18^\circ 09' 11.721''; at the end of the month, the Sun’s apparent RA and Dec are 10^h 35^m 53.313^s and +08^\circ 50' 29.687''. This month, the Sun moves from Cancer to Leo. August 8, 04:33 is Liqiu (Beginning of Autumn), solar longitude 135^\circ. August 23, 19:21 is Chushu (End of Heat), solar longitude 150^\circ.
Moon
The Moon passes perigee, apogee, and perigee on August 3 at 05:00, August 19 at 00:00, and August 31 at 02:00, respectively. Lunar phases: First Quarter on the 6th at 19:08, Full Moon on the 14th at 02:57, Last Quarter on the 22nd at 05:54, and New Moon on the 29th at 11:04.
Mercury
Mercury is at inferior conjunction on August 17. Before the 17th, it is an evening star, approaching the Sun and difficult to observe. After inferior conjunction, it becomes a morning star, rapidly moving away from the Sun and appearing in the northeastern sky before dawn. Conjunctions: Aug 1 at 19:00 (1^\circ N of Moon), Aug 28 at 09:00 (3^\circ N of Moon). Stationary on Aug 2 and Aug 26.
Venus
In August, Venus is close to the Sun and difficult to observe. On August 16, Venus is at superior conjunction, completely hidden by the Sun’s glare. After superior conjunction, it moves to the east of the Sun and becomes an evening star.
Fire (Mars)
Mars moves from Taurus to Gemini. Its rising time in the east gradually advances to around 01:30, with a brightness of about +1.4 magnitude; observation conditions are improving. On the 25th at 22:00, Mars is in conjunction with the Moon (3^\circ N).
Jupiter
Jupiter moves in Aries. On August 31, it becomes stationary and begins retrograde motion. In August, its rising time advances to around 22:00, with a brightness of about -1.5 magnitude. The second half of the night is a good time for observation. On the 20th at 20:00, Jupiter is in conjunction with the Moon (5^\circ S).
Saturn
Saturn is in direct motion in Virgo. In August, it is located in the southwestern sky at sunset with a brightness of about +0.9 magnitude. Its setting time advances to around 21:00, leaving less time for observation. On the 4th at 20:00, Saturn is in conjunction with the Moon (8^\circ N).
(Content from "Astronomy Enthusiasts", "Astronomical Overview", Skylook, and the Internet)
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