"Golden September and Silver October" has now become a common term used by businesses in various industries to describe the annual peak sales season. In fact, the crisp autumn months of September and October are also excellent times for astronomical observation. First of all, after a whole summer of rain, there are more sunny days in autumn, which is particularly evident in the northern regions of China. Obviously, the night weather during this period is not too cold yet, so even observing all night will not be too painful. There are many highlights in the night sky in October. Although the altitude of Venus and Mars at sunset is already very low and the observation conditions are poor, Jupiter has just passed opposition and is in an ideal period for observation. In addition, the Orionid meteor shower will also reach its peak this month, although observations will be affected by moonlight.
Table of Astronomical Phenomena
Oct 01, 09:00: Saturn in conjunction with the Sun
Oct 06, 22:00: Moon at perigee
Oct 08, 03:00: Venus stationary
Oct 09, 24:00: Venus in conjunction with the Moon
Oct 10, 10:00: Mars in conjunction with the Moon
Oct 17, 09:00: Mercury in superior conjunction with the Sun
Oct 18, 06:00: Neptune in conjunction with the Moon
Oct 19, 02:00: Moon at apogee
Oct 20, 19:00: Jupiter in conjunction with the Moon
Oct 20, 23:00: Uranus in conjunction with the Moon
Oct 29, 09:00: Venus in inferior conjunction with the Sun
Moon Phases
Oct 01, 12:00: Last Quarter
Oct 08, 03:00: New Moon
Oct 15, 05:00: First Quarter
Oct 23, 10:00: Full Moon
Oct 30, 21:00: Last Quarter
October 09: Venus in Conjunction with the Moon
The current observable period of Venus appearing on the east side of the Sun for nearly nine months is finally coming to an end. Generally speaking, because the declination of Venus was lower than the Sun’s declination in most cases, its altitude at sunset was at most only 27 degrees, making observation conditions average. During this period, several important astronomical phenomena took place, including the lunar occultation of Venus visible in parts of China on the evening of May 16, and the four-planet alignment with the Moon on August 13.
The Venus-Moon conjunction occurring on October 9 is the last one we might observe in the evening this year. Around 0:00 on the 10th, the angular distance between the two is at its closest, just over 2 degrees, but we certainly cannot see Venus and the Moon at that time. At sunset on the evening of the 9th, the altitude of both is only about 5 degrees. Although the observation conditions are not great, if the transparency is excellent, we still have a chance to observe them. Not long ago, while observing the Perseid meteor shower in the grasslands, I saw the thin crescent moon of the second day of the lunar month.
After this, Venus will gradually approach the Sun, and it will become increasingly difficult to see. On October 29, Venus will be in inferior conjunction with the Sun and will be completely hidden in the Sun’s glare. However, we won’t have to wait too long to see Venus again. By the end of October, Venus will move to the west side of the Sun to become a morning star, and its altitude at sunrise will increase rapidly. Soon, we will be able to see the bright Venus in the southeastern sky in the early morning.
In addition to the Venus-Moon conjunction, Mars will also be in conjunction with the Moon on October 10. However, since the brightness of Mars is far less than that of Venus, it will be even more difficult to find it in the low southwestern sky at dusk. The Jupiter-Moon conjunction on the evening of October 20 will be much easier to observe, because Jupiter, which has just passed opposition, can reach a magnitude of -2.3, and the waxing gibbous moon on the 13th day of the lunar month is also very bright. At 19:00 that day, the angular distance between the two is more than 6 degrees; you can try to photograph it with a camera.
October 21: Orionid Meteor Shower Peak
After observing the Jupiter-Moon conjunction on October 20, we will welcome the peak of the Orionid meteor shower in the early morning of October 21. As one of the meteor showers brought to us by Halley’s Comet, the Orionid meteor shower is not particularly famous, mainly because its flow rate is not very large. The ZHR (Zenithal Hourly Rate) of the Orionids at its peak is only about 30, which certainly cannot compare with the Perseids and Geminids, which have a ZHR of over 100, nor has it had a major outburst like the Leonids. However, compared with other meteor showers with smaller flow rates, the Orionid meteor shower still has many highlights.
First, the active period of the Orionid meteor shower is from October 2 to November 7 every year, overlapping with several other meteor showers, such as the Northern and Southern Taurids and the Delta Geminids. Therefore, we can observe several meteor showers simultaneously. The meteors within the Northern and Southern Taurid groups are also very characteristic; most of them appear white, very similar to the Orionid meteors, and their radiant points are not far apart. However, the velocity of Taurid meteoroids is only 27 km/s, which forms a strong contrast with the 66 km/s of the Orionid meteoroids, allowing us to distinguish them.
On the other hand, the radiant point of the Orionid meteor shower rises at approximately 23:00 local time and reaches its highest point (culmination) around 4:00 AM. At this time, the altitude is highest, and the observed meteors are closest to the theoretical value. For observers in the Northern Hemisphere, the late night of autumn is also the period with the most sporadic meteors. Even without meteor shower activity, it should not be a problem to see more than 30 meteors in the hour before dawn. In summary, the Orionid meteor shower is very worth observing and may bring many unexpected rewards.
According to the forecast of the International Meteor Organization, the peak of the Orionid meteor shower this year is on October 21, with no expected outburst, and the peak may be relatively flat. We know that the best observation period for the Orionids is in the second half of the night. On that day, which is the 14th day of the lunar month, the moon will set at around 4:00 AM local time, about one hour before the start of astronomical twilight. At this time, there is no interference from moonlight, the radiant point is near culmination, and sporadic meteors often appear. Therefore, for us, 4:00 to 5:00 AM on the 21st will be a good opportunity to observe the Orionid meteor shower.
Return of Comets
The periodic comets returning in 2010 mainly include 2P/Encke and 103P/Hartley 2, the latter of which is likely to be the brightest.
According to their orbits, comets can be roughly divided into periodic and non-periodic comets. The "P" in the designation represents a periodic comet, which orbits the Sun with a certain period of time. The period of 2P/Encke is 3.3 years, while the familiar 1P/Halley returns once every 76 years. The orbits of non-periodic comets are usually parabolic or hyperbolic, and they only approach the inner solar system once. Comet C/2009 R1 (McNaught), which reached a magnitude of about 5 in June, is a non-periodic comet; it is now moving away from the solar system and has become very dim. Of course, if you missed the chance to observe it, there is no need for regret, as the observation conditions for Hartley 2 in October may be even better.
103P/Hartley 2 is a short-period comet that orbits the Sun every 6.47 years. It was discovered by Hartley in 1986, and its orbit has since been altered twice by the massive gravitational influence of Jupiter. In early August, it was located in the constellation Pegasus, then passed through Lacerta and Cassiopeia, and entered Perseus in October. On October 21, the comet will pass perigee, about 18 million kilometers from us. On October 28, it will pass perihelion, with an expected brightness of magnitude 4.6, visible to the naked eye. At the same time, the comet is almost opposite to the direction of the Sun, allowing for a long observation time. In fact, cases like the current return of Hartley 2 are rare; many comets have a very small angular distance from the Sun at perihelion, making them difficult to observe.
Dynamics of the Sun, Moon, and Planets
- Sun
-
At the beginning of the month, the Sun’s apparent right ascension and declination are 12h 28.3m and -3^\circ 6’; at the end of the month, they are 14h 20.4m and -13^\circ 59.9’. This month, the Sun moves from Virgo to Libra. On the 8th at 17:26, the solar term "Cold Dew" occurs, and the Sun’s celestial longitude is 195^\circ. On the 23rd at 20:35, "Frost’s Descent" occurs, and the Sun’s celestial longitude is 210^\circ.
- Moon
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The times for the Moon passing perigee and apogee are October 6 at 22:00 and October 19 at 02:00, respectively. The times for the Last Quarter, New Moon, First Quarter, Full Moon, and Last Quarter are the 1st at 11:52, 8th at 02:44, 15th at 05:27, 23rd at 09:37, and 30th at 20:46, respectively.
- Mercury
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On October 17, Mercury is in superior conjunction with the Sun, submerged in the Sun’s glare. Before the 17th, Mercury is a morning star; after the superior conjunction on the 17th, it becomes an evening star, and its angular distance from the Sun continuously increases, located in the southwestern sky at sunset. Because Mercury is too close to the Sun throughout October, it cannot be observed.
- Venus
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Lingering in Virgo, it continuously approaches the Sun, and its altitude at sunset gradually decreases. On October 29, Venus is in inferior conjunction with the Sun, rising and setting with the Sun, making it impossible to observe. After the inferior conjunction, Venus moves to the west side of the Sun to become a morning star, and its angular distance from the Sun increases rapidly. On the 8th at 03:00, Venus is stationary. On the 9th at 24:00, Venus is in conjunction with the Moon, located 3^\circ south of the Moon.
- Mars
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Moving prograde from Libra to Scorpius. At sunset, Mars is low in the southwestern sky and sets shortly after, making it difficult to observe. On the 10th at 10:00, Mars is in conjunction with the Moon, located 4^\circ north of the Moon.
- Jupiter
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Moving retrograde in Aquarius. At sunset, Jupiter is in the southeastern sky with a brightness of about magnitude -2.8. It sets at approximately 03:50 the next morning. It is still a good period for observing Jupiter this year. On the 20th at 19:00, Jupiter is in conjunction with the Moon, located 7^\circ south of the Moon.
- Saturn
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Moving prograde in Virgo. On the 1st at 09:00, Saturn is in conjunction with the Sun, rising and setting almost simultaneously with the Sun, making it impossible to observe. After the conjunction, Saturn moves to the west side of the Sun and gradually moves away. Throughout October, the angular distance between Saturn and the Sun is too close, making it difficult to observe.
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