Happy New Year: Important Astronomical Phenomena in February 2010

February 3: Saturn in Conjunction with the Moon

February 5: Mars in Conjunction with the Beehive Cluster (M44)

Mars is the closest outer planet to Earth. Its average orbital radius around the Sun is 1.52 AU (approximately 227 million kilometers). Around the time of its opposition, its distance from Earth ranges from about 50 million to 100 million kilometers. Consequently, the apparent motion of Mars is quite noticeable.

In most cases, Mars moves from west to east relative to the background stars, which is the normal reflection of its revolution around the Sun in that direction; we call this prograde motion. If the Earth did not revolve around the Sun, the apparent motion of Mars would always remain prograde. However, Earth not only revolves but does so with a much faster angular velocity (Earth takes about 365 days to orbit once, while Mars takes about 687 days). Therefore, the opposition in each synodic period is the moment Earth "overtakes" Mars. During the period before and after this, Mars moves from east to west relative to the background stars, which is called retrograde motion. When transitioning between prograde and retrograde motion, Mars appears to stand still; we call this a "station." Between prograde and retrograde (and back), there are two stations, and the opposition occurs between these two stations. This pattern of apparent motion applies to all solar system bodies with orbits outside Earth’s.

During the Mars opposition in January this year, it was located in the constellation Cancer. This means that during this period, Mars will cross Cancer three times—twice prograde and once retrograde. Cancer does not have very bright stars, but it contains an interesting deep-sky object: the Beehive Cluster, cataloged as Messier 44 (M44). Since this cluster lies nearly on the ecliptic, Mars will have three "close" conjunctions with it over several months. The closest angular distance occurred in early November 2009, when Mars even appeared "inside" this open cluster. The other two conjunctions occur on February 5 and April 17 of this year. This month’s conjunction is the one with the largest angular distance, approximately 3^\circ on the morning of the 5th. To photograph them together, one should not use a telescope with a focal length that is too long. On the evening of April 17, their angular distance will be at its closest, around 1^\circ. If you missed the observation last year, do not miss it this time.

In addition to the conjunction with the Beehive Cluster, another Mars-related event this month is the Mars-Moon conjunction. The moment their ecliptic longitudes are equal is around 11:00 AM on February 26. For observers in China, they will be below the horizon at that time and cannot be observed. By 20:00 that evening, the Moon and Mars will have separated by about 8^\circ, but the Moon will be in conjunction with M44 with an angular distance of only 3^\circ. However, the Moon will be near full phase, and its dazzling light will almost drown out the -0.7 magnitude Mars, let alone the Beehive Cluster. Although M44 is visible to the naked eye under low light pollution, you will likely need binoculars to find it at this time.

February 8: Peak of the \alpha-Centaurids Meteor Shower

Most major meteor showers occur in the second half of the year, such as the Perseids in mid-August, the Leonids in mid-to-late November, the Geminids in mid-December, and the Quadrantids in early January. The first half of the year is generally a low period for meteor showers, especially in February and March. Here, we introduce a southern meteor shower occurring in early February—the \alpha-Centaurids. It has entered our sights this year due to predictions of a small-scale outburst.

Centaurus covers a large area and contains many bright stars. Due to its low declination, only a few regions in southern China can fully appreciate it, particularly the two brightest stars, Alpha Centauri (Rigil Kentaurus) and Beta Centauri (Hadar), which are located at the southernmost part of the constellation. The radiant of the \alpha-Centaurids is located between these two bright stars, with a declination of approximately -59^\circ. Therefore, regions north of 31^\circ N latitude cannot observe this shower. However, since the theoretical flow increases with the altitude of the radiant, the best observation sites are in the Southern Hemisphere. In China, observation conditions are acceptable only in Guangdong, Guangxi, Hainan, Hong Kong, Macau, and Taiwan.

The active period of the \alpha-Centaurids lasts from late January to late February. According to current forecasts, the peak is likely to occur around 13:00 Beijing Time on February 8. For China, the time before dawn on that day may be the best window for observation. Most meteor shower observation data comes from the Northern Hemisphere, primarily because there are fewer observers in the Southern Hemisphere. Consequently, the major showers we are familiar with are those with good conditions in the North. However, many southern showers are worth observing, and the \alpha-Centaurids is one of them. Historical statistics from 1988 to 2007 show that the Zenithal Hourly Rate (ZHR) at peak was around 6. However, in 1974 and 1980, there were records of the ZHR reaching 20 to 30 within a few hours. Will a similar outburst occur this year? The best way to find the answer is to observe in the early morning of the 8th.

In addition to the constraints of the radiant’s altitude, the influence of moonlight cannot be ignored this year. Although the 8th is past the Last Quarter Moon, the phase is still over 30%. Taking observation on Hainan Island as an example, the radiant and the Moon will both rise around 2:30 AM, so observations will be subject to moonlight interference. By 5:30 AM, when the radiant reaches its upper culmination, its altitude will only be 10^\circ, and morning twilight will already be affecting visibility.

Despite the less-than-ideal conditions, the \alpha-Centaurids are still worth observing. This shower is characterized by bright meteors, especially fireballs, making it very suitable for photography and video observation. Moreover, southern meteor showers like this deserve more attention, so we recommend it to capable meteor enthusiasts.

Planetary Dynamics:

• Sun: At the beginning of the month, the Sun’s apparent Right Ascension and Declination are 20\text{h } 57.9\text{m} and -17^\circ 11.5'; at the end of the month, they are 22\text{h } 43.5\text{m} and -8^\circ 03.3'. This month, the Sun moves from Capricornus to Aquarius.

  • Feb 4, 06:48: Lichun (Beginning of Spring), solar longitude 315^\circ.

  • Feb 19, 02:36: Yushui (Rain Water), solar longitude 330^\circ.

• Moon: The Moon passes apogee and perigee on Feb 13 at 10:00 and Feb 28 at 06:00, respectively. Last Quarter, New Moon, and First Quarter occur on the 6th at 07:48, 14th at 10:51, and 22nd at 08:42. On the 8th at 03:00, the Moon occults Antares, with Antares 1.1^\circ south of the Moon.

• Mercury: Morning star. Located low in the southeastern sky before sunrise with a magnitude of -0.3. Its distance from the Sun decreases daily, making it difficult to observe. On the 12th at 14:00, Mercury is in conjunction with the Moon, 2^\circ south of the Moon. On the 27th at 13:00, Mercury is in conjunction with Neptune, 2^\circ south of Neptune.

• Venus: Evening star. Its distance from the Sun increases slowly. In February, Venus remains too close to the Sun for observation.

• Mars: Retrograde in Cancer. Located in the northeastern sky at sunset, moving to the southeastern sky in late February. Magnitude is approximately -1.0. Visible almost all night, this remains the best period for observing Mars this year. On the 26th at 13:00, Mars is in conjunction with the Moon, 5^\circ north of the Moon.

• Jupiter: Prograde in Aquarius. Difficult to observe due to its proximity to the Sun. On the 15th at 13:00, Jupiter is in conjunction with the Moon, 5.0^\circ south of the Moon. On the 28th at 19:00, Jupiter is in conjunction with the Sun, rising and setting with it, making it impossible to observe.

• Saturn: Retrograde in Virgo. In February, Saturn’s rising time moves earlier to 20:30, with a magnitude of approximately +0.6. This is a good time for observation. On the 3rd at 10:00, Saturn is in conjunction with the Moon, 8.0^\circ north of the Moon.

• Uranus: Located in Aquarius. On the 17th at 03:00, Uranus is in conjunction with the Moon, 6^\circ south of the Moon.

• Neptune: Located in Capricornus. On the 15th at 07:00, Neptune is in conjunction with the Sun.

(Content compiled by Scientific Space. Resources provided by "Amateur Astronomer" magazine, "2010 Astronomical Phenomena Supplement", and Skylook.Org. With thanks.)

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