From the beginning of 2007 to today, the astronomical forecasts I have written have accompanied everyone for four years. As another year draws to a close, let me begin this issue by reviewing the spectacular astronomical events of this year. Although we lacked a total solar eclipse observable within China, the excitement of this year’s phenomena was by no means inferior to the previous two years. The annular solar eclipse on January 15th sparked another wave of astronomical interest, and observations in most areas within the path of annularity in China were very successful. I hope that when the total lunar eclipse occurs in December, the weather in the Northeast will be as favorable as ever. The Perseid meteor shower in the summer remained eye-catching, and I believe everyone must be full of expectations for the Geminid meteor shower at the end of the year. Additionally, the partial lunar eclipse on June 26th and the “four planets accompanying the moon” in mid-August may have left a deep impression on you. Regarding comets, the non-periodic comet C/2009 R1 was quite stunning; not only did its brightness once reach about magnitude 4, but two comet tails were clearly visible in photos taken by many enthusiasts. In October, comet 103P passed perihelion and reached naked-eye visibility, though its tail was not very prominent. In short, 2010 has had no shortage of highlights, and as an astronomy enthusiast, you must have gained a lot. Next, let’s look at the exciting astronomical events coming up in the last month of 2010.
Astronomical Overview
01st: Mercury at Eastern Elongation, altitude 10^\circ
02nd: Saturn in conjunction with the Moon
03rd: Venus in conjunction with the Moon
04th: Venus at greatest brilliance, magnitude -4.9
06th: Uranus stationary
07th: Occultation of Mars by the Moon
07th: Mercury in conjunction with the Moon
07th: Geminid meteor shower activity period begins
10th: Mercury stationary
11th: Neptune in conjunction with the Moon
14th: Jupiter in conjunction with the Moon
14th: Mercury and Mars
14th: Uranus in conjunction with the Moon
14th: Geminid meteor shower peak, ZHR 120 to 200
17th: Geminid meteor shower activity period ends
20th: Mercury at inferior conjunction
22nd: Winter Solstice at 06:00
29th: Saturn in conjunction with the Moon
30th: Mercury stationary
Lunar Dynamics
01st: Moon at perigee
06th: New Moon
13th: Moon at apogee, First Quarter
21st: Total Lunar Eclipse
25th: Moon at apogee
28th: Last Quarter
December 1: Mercury at Eastern Elongation
During eastern elongation, Mercury is an evening star and appears low in the sky at sunset. Conversely, during western elongation, Mercury is a morning star and can be observed before sunrise. For most people, the evening observation time is clearly more convenient, so the eastern elongation of Mercury receives more attention. In fact, the public with astronomical observation experience will feel that when weather conditions are similar, the atmospheric transparency at dawn is usually better than at dusk. Therefore, if you want to observe Mercury, it is recommended to wake up early during a western elongation for better results.
Of course, for different elongations, the altitude of Mercury at sunrise or sunset varies greatly, determined by the observer’s latitude and the declination difference between Mercury and the Sun. During this eastern elongation on December 1st, the angular distance between Mercury and the Sun is not large, only 21^\circ. Since its declination is lower than the Sun’s, Mercury’s altitude at sunset is only about 10^\circ. Because Mercury’s brightness is only magnitude -0.5 at this time, it is almost impossible to observe it with the naked eye at sunset. Therefore, for our mid-to-high latitude regions in the Northern Hemisphere, the observation conditions for this eastern elongation are not ideal. However, if the atmospheric transparency is excellent that day, you can try to find a place with a very open western horizon and attempt to view Mercury with the naked eye.
December 14: Geminid Meteor Shower Peak
At the end of the year, we welcome the arrival of the Geminid meteor shower. Although the Geminids rarely show large-scale outbursts, their flow can often be maintained at a high level, with a peak ZHR (Zenithal Hourly Rate) of around 120 to 200. Besides the large flow, the meteors within the Geminid group have distinct characteristics. First, the color is whitish, which is more conducive to visual observation. Second, the meteoroid velocity is relatively slow, about 35 km/s; the slower the speed, the more favorable it is for photographic observation. Furthermore, the Geminid shower has many bright meteors, especially fireballs that often appear before the peak. Additionally, its radiant point in the constellation Gemini rises from the east almost as soon as it gets dark, making it possible to observe meteors throughout the night. Therefore, this meteor shower is very suitable for astronomy enthusiasts and even the general public to conduct observation activities.
For most parts of China, observations of the Geminid peak this year will be interfered with by moonlight to some extent. On December 7th, when the shower begins its activity, moonlight has almost no impact. However, as the flow increases, the lunar phase also grows, and the moonset time is delayed. According to the current forecast from the International Meteor Organization (IMO), the peak of the Geminids this year may occur at 19:00 Beijing time on December 14th (with a peak value of about 120 meteors per hour). At that time, the radiant point will have already risen in eastern China. Theoretically, seeing meteors should be no problem, but the First Quarter moon (9th day of the lunar month) will be in the sky, and its impact on observation cannot be ignored. However, by 01:00 on the 15th, the moon will set, and observation conditions thereafter should be good. The Geminid peak lasts a long time, and we will see many meteors several hours before and after the peak. Even if the peak has passed, there is no need to worry; the entire night from the 14th to the 15th is suitable for observation. If you are interested and the weather is good, the flow on the night of the 13th will also be very considerable and worth monitoring. After the 15th, the Geminid flow will drop rapidly, and the activity period will end by December 17th. Finally, a reminder for those in northern China: the weather is already very cold during the Geminid activity period and the nights are long. If you plan to observe all night, be sure to keep warm, travel with others, and ensure safety.
December 21: Total Lunar Eclipse
Compared to solar eclipses, lunar eclipses receive significantly less attention. In fact, lunar eclipses, especially total lunar eclipses, are astronomical events of great aesthetic value. After the Moon completely enters the Earth’s umbra, the only sunlight that can reach it is the long-wavelength light refracted by the Earth’s atmosphere. Therefore, the lunar surface appears copper-colored, which is what we commonly call the “Blood Moon.” At the moment of third contact (the end of totality), when a small part of the lunar surface returns to the brightness of a full moon, the entire sky seems to be illuminated, a truly shocking sight.
At least two solar eclipses occur on Earth every year, with a total solar eclipse occurring roughly every two years. Theoretically, it is possible for no lunar eclipse to occur globally in a single year. However, whether it is a partial or total lunar eclipse, about half of the Earth can observe it when it happens, which is a major difference from solar eclipses. But for a fixed observation site, it is not easy to observe a complete total lunar eclipse. A total lunar eclipse from first contact to fourth contact lasts more than three hours, during which the Moon must remain above the horizon and the weather must stay clear. Of course, these are also the basic conditions for capturing a composite sequence image of the lunar eclipse.
For this total lunar eclipse, observers in China will find it difficult to capture a complete composite sequence image. The regions where the entire process is visible are mainly Central and North America, eastern Siberia, and the Pacific region. At 13:29 Beijing time on December 21st, the Moon will enter the penumbra. At 14:32, the first contact occurs, and the eclipse officially begins, but at this time the Moon is still below the horizon for all of China. It is not until 15:40, the moment of second contact (totality begins), that the Moon can be observed in a small part of Northeast China. At 16:17, the maximum eclipse occurs with a magnitude of 1.25, still only visible in a small part of the country. By 16:53, before third contact (totality ends), the Moon will have risen in the Northeast, northern North China, and the Shandong Peninsula. Friends in these areas can find a place with an unobstructed northeastern horizon to enjoy the partial eclipse. It is not until 19:06, when the penumbral eclipse ends, that the Moon will have risen in the westernmost parts of China. Although the observation conditions for this eclipse are not ideal, there will be two total lunar eclipses visible in China in 2011, on June 16th and December 10th, with the December 10th eclipse being visible in its entirety across China. You might as well treat this observation as a rehearsal to prepare for next year.
December 22: Ursid Meteor Shower Peak
The Ursid meteor shower is often the finale of the year’s spectacular astronomical events. The activity period for this shower is from December 17th to December 26th. In terms of timing, it connects well with the Geminid meteor shower, but in reality, the flow of the Ursids is much lower. Historically, the Ursids have had large outbursts, notably in 1945 and 1986, but the predicted flow for this year is not optimistic, with the peak occurring on December 22nd and a ZHR of only about 10. The lunar phase on that day is a full moon, so the few meteors will appear even dimmer under the interference of moonlight. The greatest advantage of the Ursid meteor shower is that its radiant point has a declination of +76^\circ, placing it within the circle of perpetual apparition, meaning meteors can be observed all night. The meteoroid velocity of 33 km/s is not fast, but the shower does not have many bright meteors, and the weather will be very cold during observation, which everyone should keep in mind.
Year-end Solar Terms: Major Snow and Winter Solstice
December 7th at 13:38 marks the solar term “Major Snow” (Daxue) in the lunar calendar, when the Sun’s celestial longitude reaches 255 degrees. Astronomical experts explain that “Major Snow” means the weather is colder and the probability of snowfall is greater than during “Minor Snow.” According to the Collected Explanations of the Seventy-Two Hou of the Lunar Calendar: “Major means abundance; at this point, the snow is abundant.” It can be seen that the Major Snow solar term indicates the starting time and degree of heavy snowfall during this period. Like Minor Snow, Grain Rain, and Grain in Ear, it is a solar term that directly reflects precipitation.
During Major Snow, the climate enters mid-winter, and the Chinese mainland is completely controlled by the Mongolian cold high-pressure system, with snowfall beginning to increase. In northern China, it is a world of silver-wrapped ice and snow, while Jiangnan enters the deep winter season with significantly dropping temperatures and frequent freezing. Southern regions have a milder winter climate with less rain and snow, with average temperatures about 2^\circC to 4^\circC higher than the middle and lower reaches of the Yangtze River, and rainfall accounting for only about 5% of the annual total. Occasional snowfall mostly occurs in January and February; snow cover on the ground is rarely seen more than once every three to five years. If one can witness the earth covered in white snow and green trees adorned in silver, it will be an unforgettable experience.
December 22nd at 07:38 is the Winter Solstice (Dongzhi), when the Sun’s celestial longitude is 270 degrees. The Winter Solstice is a very important solar term in the Chinese lunar calendar and a traditional festival; many places still maintain the custom of celebrating it. It is also known as the “Winter Festival,” “Longest Reach Festival,” or “Sub-Year.” As early as the Spring and Autumn Period over 2,500 years ago, China used the gnomon (tugui) to observe the Sun and determine the Winter Solstice, making it the earliest of the twenty-four solar terms to be established. The Winter Solstice is the day with the shortest daylight and longest night of the year in the Northern Hemisphere; after this day, the daylight hours gradually lengthen. The ancients said of the Winter Solstice: the peak of Yin, the birth of Yang Qi, the Sun’s southernmost reach, the shortest day, and the longest shadow, hence it is called “Winter Solstice.” After the Winter Solstice, the climate everywhere enters the coldest stage, known as “Entering the Nine” (Jin Jiu). There is a folk saying in China: “The coldest days are in the third nine-day period, and the hottest are in the three dog days.”
Modern astronomical science determines that on the day of the Winter Solstice, the Sun shines directly on the Tropic of Capricorn, the sunlight is most tilted toward the Northern Hemisphere, and the Northern Hemisphere has the shortest day and longest night. After this day, the Sun gradually moves north again.
Solar System Dynamics
Sun: Moves from Scorpio through Ophiuchus to Sagittarius. Major Snow on the 7th at 13:38, Winter Solstice on the 22nd at 07:38.
Moon: At apogee on the 13th at 17:00; at perigee on the 1st at 03:00 and the 25th at 20:00. New Moon on the 6th at 01:36, First Quarter on the 13th at 21:59, Full Moon on the 21st at 16:13, Last Quarter on the 28th at 12:18. Total Lunar Eclipse on the 21st.
Mercury: Evening star. Greatest Eastern Elongation on the 1st at 23:00, located low in the southwest at sunset with an altitude of about 10 degrees and a brightness of -0.5 mag, difficult to observe. Inferior conjunction on the 20th, transitioning from evening star to morning star.
Venus: Moves from Virgo to Libra. Located in the southeastern sky before sunrise, with an altitude of over 31 degrees at sunrise. Venus in conjunction with the Moon on the 3rd at 05:00 (Venus 6^\circ north of the Moon). Greatest brilliance on the 4th at 23:00, magnitude -4.9.
Mars: Moves from Ophiuchus to Sagittarius. Located low in the southwest at sunset, difficult to observe due to proximity to the Sun.
Jupiter: Moves from Aquarius to Pisces. Located in the south at sunset, sets around midnight, brightness -2.4 mag. Jupiter in conjunction with the Moon on the 14th at 10:00 (Jupiter 7^\circ south of the Moon).
Saturn: In Virgo, rises in the southeast around 01:20, brightness 0.8 mag. Saturn in conjunction with the Moon on the 2nd at 02:00 and the 29th at 11:00 (Saturn 8^\circ north of the Moon).
Uranus: In Pisces, brightness 5.8 mag. Uranus in conjunction with the Moon on the 14th at 14:00 (Uranus 7^\circ south of the Moon).
Neptune: In Capricorn, brightness 7.9 mag.
Asteroid: Asteroid 16 Psyche at opposition on the 9th, magnitude 9.4, located near Aldebaran in Taurus.
(Content from “Astronomy Enthusiasts” and “Astronomical Overview”, images from the internet and Stellarium, compiled by Scientific Space)