In the cool and refreshing month of September, the celestial theater gradually becomes lively. The nights around the Autumnal Equinox are the time of year when sporadic meteors appear most frequently. Especially in the later half of the night, if the weather is clear, seeing twenty to thirty sporadic meteors per hour is not a problem. At the same time, the autumn night sky is full of highlights: the beautiful Andromeda Galaxy (M31) is visible to the naked eye, and deep-sky objects like the Triangulum Galaxy (M33) are also popular targets for astronomical enthusiasts. Additionally, Uranus will reach opposition this month, providing excellent observation conditions.
On September 12, we will welcome one of the most important festivals of the year—the Mid-Autumn Festival. Whether you are a “stranger in a strange land” or at home with your family, BoJone wishes to “raise my head to view the bright moon” with you. I wish everyone a happy, beautiful, and reunited Mid-Autumn Festival in advance!
Grand View of Celestial Phenomena
01st 18:06 Moon conjunct Spica: 2.2^\circ N
03rd 13:59 Mercury Greatest Elongation: 18.1^\circ W
08th 16:45 Mars conjunct Pollux: 5.9^\circ S
09th 10:18 Mercury conjunct Regulus: 0.7^\circ N
12th Happy Mid-Autumn Festival!
18th 14:46 Moon conjunct Pleiades: 2.8^\circ N
23rd 16:23 Moon conjunct Mars: 4.9^\circ N
23rd 17:05 Autumnal Equinox
26th 07:41 Uranus at Opposition
29th 04:07 Mercury at Superior Conjunction
Lunar Dynamics
05th 01:39 First Quarter Moon
12th 17:27 Full Moon
20th 21:39 Last Quarter Moon
27th 19:09 New Moon
September 1: Peak of the Aurigid Meteor Shower
The first to enter our field of vision this month is the \alpha Aurigid meteor shower. This shower actually begins its activity around August 25 and continues until about September 5. In recent years, through the analysis of observation data, the position of its radiant has been further confirmed. However, there is still no consensus on the flow rate at its peak. It is generally believed that the peak duration of this meteor shower is very short and highly sudden, making it easy to miss. Historically, Zenithal Hourly Rates (ZHR) of 30 to 40 were only recorded in 1935, 1986, and 1994. Furthermore, only three observers recorded the peaks in 1986 and 1994, leading scientists to believe that some peaks must have been missed. Indeed, in 2007, although the lunar phase was unfavorable, an outburst of the \alpha Aurigids was monitored in western North America, with the ZHR reaching over 130. Radar data also showed a smaller outburst shortly after the peak, but due to heavy moonlight and the likelihood that most meteors were faint, observers did not see this subsequent outburst.
For the Aurigid meteor shower, the radiant does not reach an ideal height until the latter half of the night. This year’s predicted peak occurs at 21:00 Beijing time on September 1. For most parts of China, it will not be observable at that time, making the pre-dawn hours of September 2 a better time for observation. The good news is that this year’s peak coincides with a New Moon, so observations will not be affected by moonlight. However, when observing this type of meteor shower, one should be prepared for disappointment; the rate may drop very quickly after the peak, and the number of shower meteors we observe might be far fewer than sporadic meteors.
September 3: Mercury at Greatest Western Elongation
Less than two months after the eastern elongation on July 20, Mercury will reach its third western elongation of the year. The dawn of September 3 will be another excellent opportunity to observe Mercury this year.
For inferior planets, the moment we see them at the maximum angular distance from the Sun on either side from Earth is called the greatest elongation. The quality of Mercury’s observation conditions is mainly reflected in its altitude above the horizon at sunrise or sunset. Besides the angular distance between Mercury and the Sun, it is also closely related to the difference in their declination. This is why not all greatest elongations offer good observation conditions, and sometimes conditions might be better shortly before or after the actual elongation.
During this elongation, the angular distance between Mercury and the Sun is approximately 18^\circ. Since Mercury’s declination is higher than the Sun’s, observation conditions are favorable for the Northern Hemisphere. Taking the region around 40^\circ North latitude as an example, Mercury’s altitude at sunrise on September 3 is already 16^\circ, with a brightness of about -0.2 magnitude. The half-hour or so before sunrise is the best time for observation. In fact, observation conditions for Mercury are quite good for several days around this elongation. As long as the weather is clear, you can wake up early and find a place with an unobstructed eastern horizon to try and spot Mercury.
September 10: Peak of the \epsilon Perseid Meteor Shower
Even when it was previously known as the September Perseids, many astronomical enthusiasts were likely unfamiliar with it. Due to its very small flow rate, this meteor shower was once almost forgotten by scientists. In 2008, a gentle peak containing brighter meteors was observed, with the radiant located near the star \epsilon Persei. Consequently, the name “September Perseids” became history, replaced by the \epsilon Perseid meteor shower.
According to the International Meteor Organization’s forecast, the 2011 peak of the \epsilon Perseids will occur around 06:00 Beijing time on September 10. By then, it will already be daylight in most parts of China, making conventional optical observations impossible. Therefore, interested friends can observe from the night of the 9th to the early morning of the 10th. The waxing gibbous moon will have some impact during the first half of the night, but conditions will be more ideal in the second half. It is also a reminder that unless an outburst occurs, the flow rate of the \epsilon Perseids will be very small; it is suitable for scientific observation but not for general appreciation.
September 12: Happy Mid-Autumn Festival!
September 26: Uranus at Opposition
For a long time before the invention of the telescope, people only recognized five planets in the solar system besides Earth: Mercury, Venus, Mars, Jupiter, and Saturn. In 1609, Galileo applied the telescope to astronomical observations, and many objects previously invisible to the naked eye gradually entered human sight. Later, the aperture of astronomical telescopes grew larger, and different types of optical systems appeared. With increased aperture and longer focal lengths, the resolution of telescopes improved. Although stars still appear as points of light in a telescope, planets closer to us can be observed as visible disks. Before Uranus was confirmed as a planet, it had been observed many times. Because it was located in the Taurus region at the time, it was even given a stellar designation—34 Tauri. On March 13, 1781, when William Herschel observed it with a telescope in his backyard, he noticed it had a fuzzy disk. Although he privately suspected the object was more like a planet, he initially claimed to have discovered a comet. In 1783, the French scientist Laplace confirmed that Herschel had discovered a planet, but it was not officially named Uranus, after the Greek god of the sky, until after 1823.
As one of the most important astronomical discoveries in human history, Uranus doubled the known scale of the solar system at the time. Its average distance from the Sun is about 2.869 billion kilometers, and it takes 84.3 years to complete one orbit. Therefore, its brightness is faint, and its proper motion relative to background stars is slow. Usually, the visual magnitude of Uranus is around 6.0, and even at opposition, it is only 5.7. Recently, Uranus has been located in the Pisces region; to observe it, one still needs at least a pair of binoculars.
Solar System Body Dynamics
- Sun
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At the beginning of the month, the Sun’s apparent right ascension and declination are 10^h 39^m 31.263^s and +08^\circ 28' 52.969''; at the end of the month, they are 12^h 23^m 50.785^s and -02^\circ 34' 41.211''. This month, the Sun moves from Leo to Virgo. On the 8th at 07:34, it is White Dew (Bailu), with the Sun’s ecliptic longitude at 165^\circ. On the 23rd at 17:05, it is the Autumnal Equinox, with the Sun’s ecliptic longitude at 180^\circ.
- Moon
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The times for apogee and perigee are September 15 at 14:00 and September 28 at 09:00, respectively. The lunar phases for First Quarter, Full Moon, Last Quarter, and New Moon are the 5th at 01:39, 12th at 17:27, 20th at 21:39, and 27th at 19:09.
- Mercury
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Before September 29, Mercury is a morning star, appearing in the northeastern sky before dawn. On September 3, Mercury reaches greatest western elongation, with a maximum angular distance of 18^\circ from the Sun, an altitude of about 16^\circ at sunrise, and a brightness of about -0.2 magnitude, marking the third best period to observe Mercury this year. After the elongation, Mercury approaches the Sun and reaches superior conjunction on September 29, making it unobservable. Thereafter, Mercury becomes an evening star on the eastern side of the Sun, increasing its angular distance and appearing low in the southwestern sky after sunset. On the 9th at 10:00, Mercury is conjunct Regulus, with Mercury 0.7^\circ north of Regulus.
- Venus
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Evening star. In September, Venus is close to the Sun and difficult to observe. On the 30th at 19:00, Venus is conjunct Saturn, with Venus 1^\circ south of Saturn.
- Mars
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Mars moves prograde from Gemini to Cancer. The rising time of Mars gradually advances to around 01:00, with a brightness of about +1.4 magnitude; observation conditions are gradually improving. On the 10th at 11:00, Mars is conjunct Pollux, with Mars 6^\circ south of Pollux. On the 23rd at 16:00, Mars is conjunct the Moon, with Mars 5^\circ north of the Moon.
- Jupiter
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Jupiter is in retrograde in Aries. In September, Jupiter’s rising time further advances to around 20:00, with a brightness of about -2.8 magnitude, making it an excellent time for observation. On the 17th at 02:00, Jupiter is conjunct the Moon, with Jupiter 5^\circ south of the Moon.
- Saturn
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Saturn is in prograde in Virgo. In September, Saturn is in the southwestern sky at sunset and sets shortly after, making it difficult to observe. On the 1st at 07:00, Saturn is conjunct the Moon, 7^\circ north of the Moon. On the 28th at 22:00, Saturn is conjunct the Moon again, 7^\circ north of the Moon.
(Content sourced from “Amateur Astronomer”)
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