In the upcoming month of August, exciting astronomical phenomena will emerge one after another. On the 13th of this month, not only will we be visited by the Perseid meteor shower under excellent observation conditions, but there will also be the highly anticipated “four planets accompanying the Moon” in the western evening sky. Both Mercury and Venus will reach their greatest eastern elongations, and the brilliant light of various planets will unveil the prelude to planetary observation. Overall, if the weather does not disrupt the plans, these spectacular celestial events will surely not disappoint astronomy enthusiasts. August is the height of summer, with clear skies and fresh air, making it an ideal time for observation. Astronomy enthusiasts often regret the shortness of the nights. In August, the celestial wonders remain, and the passion remains.
Dance of the Sky
02nd 04:00 Mars conjunction Saturn
05th–15th Gathering of Venus, Mars, and Saturn
07th 09:00 Mercury at greatest eastern elongation
08th Venus conjunction Saturn
13th Early morning: Perseid meteor shower peak
13th 03:00 Saturn conjunction Moon, 15:00 Venus conjunction Moon, 16:00 Saturn conjunction Moon; in the evening, Venus, Saturn, and Mars accompany the Moon
14th 01:00 Mars conjunction Moon
18th 10:00 Venus conjunction Mars
20th 12:00 Mercury stationary, turning retrograde; Venus at greatest eastern elongation
20th 18:00 Neptune at opposition
14th 20:00 Neptune conjunction Moon
27th 15:00 Uranus conjunction Moon; 20:00 Jupiter conjunction Moon
The Moon
The Moon passes apogee, perigee, and apogee at: August 11, 02:00; August 25, 14:00.
Last Quarter: 3rd, 12:59
New Moon: 10th, 11:08
First Quarter: 17th, 02:14
Full Moon: 25th, 01:05
August 7: Mercury at Greatest Eastern Elongation
The first planet to perform at the beginning of the month is Mercury, the closest planet to the Sun. Usually, we have few opportunities to see Mercury because it is always very close to the Sun and is often drowned out by the Sun’s glare. Only when Mercury appears at its maximum angular distance on either side of the Sun—known as the greatest eastern or western elongation—do we have a chance to catch a glimpse of it. Of course, if Mercury’s declination is lower than the Sun’s, observation conditions will be less than ideal even at elongation. This is the case for the greatest eastern elongation on August 7 this year. For observers on Earth, the maximum angle between Mercury and the Sun does not exceed 30^\circ; in fact, in most cases, the elongation does not reach this value. This greatest eastern elongation occurs at 09:00 Beijing Time on the 7th, with the angular distance between the Sun and Mercury reaching 27^\circ, the largest of the year. However, during this period, Mercury’s declination is about 10^\circ lower than the Sun’s. For regions at 40^\circ North latitude, Mercury’s altitude at sunset that evening will be only 11^\circ, appearing in the due west with a brightness of about 0.4 mag. Observation conditions are not very ideal.
August 13: Perseid Meteor Shower Peak
Perseid Meteor Shower Observation Guide: http://kexue.fm/archives/62
The annual Perseid meteor shower will once again grace the skies in August. For astronomy enthusiasts, especially students, the Perseid meteor shower is a feast not to be missed. As one of the three major meteor showers in the Northern Hemisphere, the Perseids are known for their stable flow. Every mid-August, its peak allows us to enjoy dozens of beautiful yellow-green meteors within an hour. Since the active period of this shower occurs in summer, the difficulty of observing it is much lower than that of the Geminids or Quadrantids in the dead of winter, making it particularly suitable for students on summer vacation.
This year, the Perseid meteor shower began its activity on July 17 and will continue until August 24. Between August 11 and 14, the flow will be quite significant. During this time, the Moon will be in its New Moon or Waxing Crescent phase, which is very favorable for meteor observation. Therefore, the observation conditions for the Perseids this year are excellent.
According to the International Meteor Organization’s forecast, the peak of the Perseid meteor shower this year is likely to occur around 07:30 on the 13th, with a ZHR (Zenithal Hourly Rate) of over 100. Although it will already be daylight across China at that time, making traditional optical observation impossible, the radiant will have already risen before dark on the 12th, allowing for all-night observation. Therefore, the period from the evening of the 12th to the dawn of the 13th should be the best time to observe the Perseids. Furthermore, since this shower showed a larger flow in 2009, multiple peaks might occur this year as well. If you are interested, you can monitor it for several consecutive days.
Meteors within the Perseid shower are characterized by high speeds and many bright meteors. Their meteoroid speed is 59 km/s, so most meteors appear very fast and fleeting. This is also one of the ways to distinguish Perseid meteors from sporadic ones.
August 13: Four Planets Accompanying the Moon
Although observation conditions for Mercury at its greatest eastern elongation are not great, its altitude at sunset will decrease slowly over the following days. By the evening of the 13th, if the weather is clear, it may still be possible to find it in the western sky at twilight. However, the main characters at this time are no longer Mercury. Venus, Mars, and Saturn, which are slightly higher in altitude, along with the waxing crescent moon on the 4th day of the lunar month, will perform a “three planets accompanying the Moon” event. If we include Mercury, which is not easily found, it can be called “four planets accompanying the Moon.”
Planets, like Earth, revolve around the Sun. From our perspective on Earth, they move relative to the background stars. Because different planets move at different speeds, situations arise where two or more planets appear close together, which we usually call a planetary conjunction or gathering. Gatherings between the inner planets (Mercury, Venus, Mars) or between them and the outer planets are relatively common. Conjunctions of two planets happen frequently, while multi-planet gatherings occur every few years, though they are sometimes difficult to observe due to their proximity to the Sun.
During this “four planets accompanying the Moon” event, Mercury is located in the constellation Leo, while the other four bodies are in Virgo. Mercury is at a greater angular distance from the others and has the lowest altitude, making it the hardest to observe. If we face west at that time, Venus (-4.3 mag) will be the easiest to find. To the right of Venus by 5^\circ is Saturn (1.1 mag), and to the left by about 3^\circ is Mars (1.5 mag). In addition to the planetary gathering, the crescent moon will appear 5^\circ below and to the left of Venus. Of course, except for Venus and the Moon, the other planets are relatively dim and not easy to observe. If the weather is not perfect, we might only see the “simplified version” of this event—Venus in conjunction with the Moon.
August 20: Venus at Greatest Eastern Elongation
Before this greatest eastern elongation, Venus has been in our line of sight for several months. Its highest altitude at sunset was 27^\circ in late May. By the time of the greatest eastern elongation on August 20, its altitude at sunset will be only 18^\circ, making observation conditions less than ideal.
Although the altitude has decreased, finding Venus is not difficult. Because Venus is near elongation, its brightness is gradually increasing. On the evening of the 20th, Venus at -4.4 mag will be very obvious in the western sky. At the same time, Mars can be found less than 2^\circ away, with Saturn about 10^\circ to the right, and Spica at a similar distance. Generally, the greatest elongation is not necessarily the time of best observation conditions, but its phase is exactly 50%. If you observe it through a telescope, you will see a scene similar to a first-quarter moon.
August 20: Neptune at Opposition
Neptune is the last of the eight classic planets to be recognized. Because it is very far from us, about 4 billion kilometers, Neptune does not emit light itself and relies entirely on reflecting sunlight. Therefore, its brightness is very weak, only 7.8 mag even at opposition. On Earth, even with a large telescope, it is difficult to distinguish its surface details. Neptune’s orbital period around the Sun is 164.8 Earth years, and its movement relative to the background stars on the ecliptic is very slow, making it hard to find in the vast sea of stars.
There are many interesting stories about the discovery of Neptune. In the mid-19th century, Uranus was well known, but its theoretical orbital parameters always differed from actual observations. Scientists predicted the existence of another distant planet affecting Uranus’s orbit. Subsequently, astronomers Adams from Britain and Le Verrier from France independently calculated Neptune’s orbit. German astronomer Galle first observed Neptune on September 23, 1846, at a position very close to the calculated one. This discovery shocked the world, and Neptune earned the nickname “the planet at the tip of a pen.”
During this year’s Neptune opposition on August 20, it is located in the constellation Capricorn. This is close to where it was first discovered 164 years ago; next year will mark the completion of its first full orbit around the Sun since its discovery. If interested, you can try to find Neptune using a small telescope in the suburbs away from urban light pollution.
Solar System Dynamics
Sun
At the beginning of the month, the Sun’s apparent right ascension and declination are 8h 44.4m, +18^\circ 05.7'; at the end of the month, they are 10h 36.8m, 8^\circ 45.3'. This month, the Sun moves from Cancer to Leo. August 7, 22:49 is Liqiu (Beginning of Autumn), solar longitude 135^\circ. August 23, 13:27 is Chushu (End of Heat), solar longitude 150^\circ.Mercury
Evening star. In early August, Mercury moves from low in the northwestern sky at sunset to low in the southwestern sky. On August 7, Mercury reaches greatest eastern elongation with a brightness of about 0.8 mag, located low in the southwest at sunset.Venus
Moves from Leo into Virgo. Evening star, located in the southwestern sky at sunset. Its altitude at sunset decreases daily from 21^\circ to 16^\circ, with a brightness of about -4.4 mag. Observation conditions are becoming less ideal.Mars
Prograde in Virgo. At sunset, Mars is in the southwestern sky with a brightness of about +1.3 mag, setting around 21:00. Observation conditions are becoming less ideal. On the 2nd at 04:00, Mars is in conjunction with Saturn, 2^\circ south of Saturn. On the 14th at 01:00, Mars is in conjunction with the Moon, 6^\circ north of the Moon.Jupiter
Retrograde in Aquarius. In August, Jupiter’s rising time in the east continues to advance to around 20:30, with a brightness of -2.8 mag, making it an excellent time for observation. On the 27th at 20:00, Jupiter is in conjunction with the Moon, 7^\circ south of the Moon.Saturn
Prograde in Virgo. Located in the southwestern sky at sunset with a brightness of about +1.1 mag. Its setting time advances further to around 20:30, leaving less time for observation. On the 13th at 15:00, Saturn is in conjunction with the Moon, 8^\circ north of the Moon.Uranus
In Pisces. Brightness 5.8 mag. On the 27th at 15:00, Uranus is in conjunction with the Moon, 6^\circ south of the Moon.Neptune
Moves from Aquarius into Capricorn. Brightness 7.8 mag. Opposition on the 20th at 18:00 in Capricorn.Meteor Showers
The Perseid meteor shower is active from July 17 to August 24. The peak is predicted for August 13 at 07:30 with a ZHR of 100. Multiple peaks are possible in 2010, and observations will not be affected by moonlight.
Source: Astronomy Enthusiasts Magazine Author: Li Xin
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