Happy New Year! Important Astronomical Phenomena in February 2011

Major Astronomical Events

01st: Venus distance from Sun: 45.4^\circ W
05th: 00:49 Mars in conjunction with Sun
08th: \alpha Centaurids meteor shower peak
12th: 05:32 Moon in conjunction with Pleiades: 1.5^\circ N
17th: 17:15 Neptune in conjunction with Sun
22nd: 09:02 Moon in conjunction with Spica: 2.8^\circ N
25th: 13:26 Moon in conjunction with Antares: 2.9^\circ S
25th: 16:27 Mercury in superior conjunction with Sun

Lunar Phases

03rd: 10:31 New Moon
11th: 15:18 First Quarter
18th: 16:36 Full Moon
25th: 07:26 Last Quarter

February 7: Jupiter in Conjunction with the Moon

Since the Moon orbits the Earth with a period of about 27 days, it completes one revolution against the background stars in the same amount of time, moving from west to east. The plane of the Moon’s orbit is called the white path (lunar path), which differs from the Earth’s orbit around the Sun—the ecliptic. The lunar path is constantly changing, but the angle between it and the ecliptic always remains around 5^\circ; this is commonly known as the ecliptic-lunar inclination. The orbits of the major planets in the solar system are nearly coplanar, meaning that from Earth, planets only appear near the ecliptic. Therefore, within one orbital period of the Moon, it will successively come close to several major planets. If a planet and the Moon happen to have the same celestial longitude at a certain moment, we say the planet is in conjunction with the Moon. Of course, the Moon’s apparent disk diameter is about half a degree; sometimes it even occults more distant planets or stars, forming a lunar occultation. Well-observed lunar occultations of bright stars are relatively rare, but conjunctions of bright stars with the Moon occur frequently.

In most cases of “planetary conjunction with the Moon,” the angular distance between the star and the Moon is still several degrees, or sometimes even further. Specific observation conditions also depend on the visibility of the planet. The Mercury conjunction on February 2 (New Year’s Eve) and the Mars conjunction on February 3 (Lunar New Year’s Day) are impossible to observe due to their close angular proximity to the Sun. On the evening of February 7, the waxing crescent moon of the fifth day of the lunar month will be in conjunction with Jupiter. We can easily find them in the sky after sunset. At that time, the angular distance between the two will be around 7^\circ, and Jupiter’s brightness will be approximately magnitude -2.1. Interested friends can use medium-to-long telephoto lenses to photograph the conjunction. If the exposure time is appropriate, one can capture both the bright Galilean moons of Jupiter and the part of the Moon’s dark side illuminated by reflected light from Earth’s atmosphere, which we call “Earthshine.”

In addition to the Jupiter conjunction, the Saturn conjunction on February 22 and the Venus conjunction in early March also offer good observation conditions. However, since Saturn is visible in the latter half of the night, it will be in conjunction with a waxing gibbous moon. As Venus is a morning star, it will inevitably be in conjunction with a waning crescent.

February 8: \alpha Centaurids Meteor Shower Peak

In 2011, the peak times for most meteor showers are unfortunately timed, either suffering from severe moonlight interference or occurring during the day, making them unsuitable for observation in China. The Perseid meteor shower in summer and the Geminid meteor shower in mid-winter are known for their stable flow, but observation conditions for both are poor this year.

The land area and population of the Northern Hemisphere are far greater than those of the Southern Hemisphere, naturally gathering more amateur astronomers and scientists. Therefore, among the meteor showers we are familiar with, those with radiants in the Northern Celestial Hemisphere are relatively more numerous. In fact, there are many meteor groups active in the Southern Celestial Hemisphere, but our current understanding of them is relatively limited.

The \alpha Centaurids (abbreviated as ACE) is a meteor group active during the Southern Hemisphere’s summer, similar in this regard to the Perseids, one of the three major meteor showers in the Northern Hemisphere. Its radiant has a declination of -59^\circ and a right ascension of 210^\circ, making it very suitable for Southern Hemisphere observations. Some parts of southern China can conduct short-term observations, while regions north of 30^\circ N latitude cannot observe it at all.

After analyzing statistical results from earlier observation data, astronomers found that the \alpha Centaurids have many bright meteors, with some fireballs exceeding magnitude -3. However, the overall flow of this meteor shower is not very large. From 1988 to 2007, the ZHR (Zenithal Hourly Rate) at the peak was only about 6. Between 1974 and 1980, records show the ZHR briefly reached around 20 to 30.

We still know very little about the \alpha Centaurids; there are far more questions than answers. If you are in a low-latitude southern region during the peak, it is worth observing. According to the International Meteor Organization (IMO) forecast, the active period for the 2011 \alpha Centaurids is from January 28 to February 21, with the peak likely occurring around 20:00 Beijing time on February 8. Taking Sanya in southern China as an example, the radiant in Centaurus does not rise until after 2:00 AM, leaving less than four hours for observation before dawn. Although the radiant’s altitude is low, the moon phase during the peak is a waxing crescent, which will not interfere with observations—a rare condition for meteor showers in 2011. Furthermore, since there is very little observational data on the \alpha Centaurids, we hope that enthusiasts with the right conditions will perform visual, photographic, or even video observations.

Speaking of Centaurus, people unfamiliar with the stars often confuse it with Sagittarius. In Greek mythology, the Centaur is a creature called “Centaurus,” with a human upper body and a horse’s lower body, known for being fast and skilled in martial arts. Despite their fearsome appearance, Centaurs were gentle and kind, never harming humans. Chiron was a kind, wise, learned, and versatile Centaur; many great heroes and figures in Greek mythology were his students. Chiron was loved and respected by all but was eventually accidentally killed by one of his students. Later, Zeus placed him in the sky, becoming the constellation Sagittarius. Sagittarius is located near the ecliptic, while Centaurus is further south. Centaurus has more bright stars than Sagittarius; its brightest star, \alpha Centauri, was called “Nanmen Er” (South Gate 2) in the Qing Dynasty, with an apparent magnitude of 0. In reality, \alpha Centauri is a triple star system, one of which is only 4.22 light-years away from our Sun—the star we often call Proxima Centauri. Additionally, the \beta star of Centaurus next to it is also quite bright, named “Mafu Yi” in Qing Dynasty star maps, with a visual magnitude of 0.6. \alpha Centauri and Mafu Yi are collectively known as the “South Gate Double Stars.” During Zheng He’s voyages to the Western Seas in the 14th century, they were even used for navigation.

Solar System Dynamics

Sun

At the beginning of the month, the Sun’s apparent right ascension and declination are 20^{\text{h}} 56^{\text{m}} 53.181^{\text{s}} and -17^\circ 15' 32.597''; at the end of the month, they are 22^{\text{h}} 42^{\text{m}} 32.761^{\text{s}} and -08^\circ 10' 46.516''. This month, the Sun moves from Capricornus to Aquarius.

Moon

The Moon passes apogee on February 7 at 07:00 and perigee on February 19 at 05:00. The times for New Moon, First Quarter, Full Moon, and Last Quarter are the 3rd at 10:31, 11th at 15:18, 18th at 16:36, and 25th at 07:26.

Mercury

At the beginning of February, Mercury continues to approach the Sun, a morning star appearing in the southeast sky at dawn. On the 25th, Mercury is in superior conjunction with the Sun, rising and setting almost simultaneously with the Sun, making it impossible to observe. After superior conjunction, Mercury moves to the east side of the Sun, becoming an evening star, gradually increasing its angular distance from the Sun and appearing low in the southwest sky after sunset. On the 2nd at 02:00, Mercury is in conjunction with the Moon, 4^\circ south of the Moon.

Venus

Venus moves from Ophiuchus into Sagittarius, located in the southeast sky at dawn. During this period, Venus further approaches the Sun, and its declination becomes increasingly lower than the Sun’s. Its elevation at sunrise gradually decreases from 24^\circ at the beginning of the month to 18^\circ at the end. Its brightness is about -4.2 magnitude, and observation conditions remain good.

Mars

Mars moves from Capricornus to Aquarius. It is close to the Sun and difficult to observe. On the 5th, Mars is in conjunction with the Sun, rising and setting with it, completely submerged in the Sun’s glare and impossible to observe.

Jupiter

Moving prograde in Pisces, it is in the southwest sky after sunset with a brightness of about -2.1 magnitude. Its setting time advances from around 21:30 to about 20:40, making observation conditions increasingly less ideal. On the 7th at 18:00, Jupiter is in conjunction with the Moon, 7^\circ south of the Moon.

Saturn

Saturn is in retrograde in Virgo, rising from the east around 21:30 with a brightness of about 0.5 magnitude. This is a good time to observe Saturn. On the 22nd at 01:00, Saturn is in conjunction with the Moon, 8^\circ north of the Moon.

(Sources: "Amateur Astronomer", NASA, Skylook, and other online resources.)