In May, at the turn of spring and summer, the weather gradually warms up. As the subsolar point moves northward, the nights will become shorter for us. However, the exciting astronomical phenomena this month have not diminished. The observation conditions for Venus are getting better and better. Following last month’s greatest eastern elongation of Mercury, it will move to the position of greatest western elongation in late May. At the beginning of the month, the \eta Aquariids meteor shower will also take place. Astronomy enthusiasts are going to be busy again.
04th 12:00 Venus in conjunction with Aldebaran
06th Peak of the \eta Aquariids meteor shower
07th 18:00 Neptune in conjunction with the Moon
10th 02:00 Jupiter in conjunction with the Moon
11th 08:00 Mercury at station, turning prograde
13th 01:00 Mercury in conjunction with the Moon
16th 18:00–19:00, Lunar occultation of Venus
20th 20:00 Mars in conjunction with the Moon
23rd 13:00 Saturn in conjunction with the Moon
26th 10:00 Mercury at greatest western elongation
Moon Phases:
06th 12:00 Last Quarter
14th 09:00 New Moon
21st 08:00 First Quarter
28th 07:00 Full Moon
Solar Terms:
May 5th: Lixia (Start of Summer) at 22:43 (Solar longitude 45^\circ, located in Aries).
May 21st: Xiaoman (Grain Buds) at 11:32 (Solar longitude 60^\circ, located in Taurus).
May 6: Peak of the \eta
Aquariids Meteor Shower
The famous Halley’s Comet has brought two major meteor showers to Earth:
the \eta Aquariids in May and the
Orionids, which peak in late October. Compared to the former, the latter
has a longer observable period and is better known to astronomy
enthusiasts.
The \eta Aquariids meteor shower is named because its radiant is close to the star \eta Aquarii. Aquarius, a constellation on the ecliptic, is best observed in the Northern Hemisphere during autumn. Since it lacks bright stars, many people may not be familiar with it, and the most common name heard is often the incorrect translation "Water Bottle Constellation" (Shuipingzuo) instead of "Precious Vase Constellation" (Baopingzuo). In fact, Aquarius covers a large area of the sky, ranking 10th among the 88 constellations, with both the ecliptic and the celestial equator passing through it. However, the brightest star in the constellation, \alpha Aquarii, is only about magnitude 3, and \eta Aquarii is only a 4th-magnitude star.
The \eta Aquariids is one of the larger meteor showers in the first half of the year. Since the radiant is located almost on the celestial equator, it can be observed from most regions on Earth. This year, its active period lasts from April 19 to May 28. During this time, in the Northern Hemisphere, especially at middle and high latitudes, the sun rises very early. When the altitude of the radiant is not ideal, regular optical observations can no longer be carried out. In the Southern Hemisphere, the observation conditions for this meteor shower are better. According to the International Meteor Organization’s forecast, the peak is likely to occur on May 6, with a theoretical Zenithal Hourly Rate (ZHR) of up to 85. In fact, forecasters do not have high expectations for this rate, hence the "*" added behind it. In most years, the ZHR of this meteor shower is between 30 and 50, and due to the limitation of the radiant’s altitude, the number of meteors we can actually observe is not many.
During the peak of the \eta Aquariids this year, moonlight interference will be serious. May 6 is the 23rd day of the third lunar month. Taking an observation point in the Beijing area as an example, the last quarter moon rises around 1:00 AM, located in Capricornus to the west of Aquarius. The radiant of the meteor shower rises above the horizon at about 2:00 AM, and by 4:00 AM, morning twilight will significantly affect observations. There is only less than an hour of time before that when observation conditions are acceptable. It is also worth noting that the speed of the \eta Aquariids meteors is about 66 kilometers per second, making them fast meteors. Of course, this only helps to distinguish them from other meteors to a certain extent.
May 16: Lunar Occultation of Venus
Lunar occultations actually happen all the time. As we know, the Moon is the Earth’s only natural satellite, and compared to other planets and stars, it is the closest, with an average distance of only 380,000 kilometers. Therefore, as seen from Earth, the Moon will always appear in front of certain celestial bodies and block them; this is the so-called lunar occultation. However, we usually only pay attention to cases where the Moon occults bright stars. Since the Moon only appears near the ecliptic, the bright stars it occults can only be bright stars near the ecliptic and several bright planets. The brightest "star" we can see is the Sun; a lunar occultation of the Sun is actually a solar eclipse, the importance of which goes without saying. Next is one of the protagonists of this event—the inferior planet Venus.
As our neighbor, Venus can reach a magnitude of -4.9 at its brightest. In May this year, its brightness is about magnitude -4. During this period, Venus is the "Evening Star," appearing in the southwestern sky at dusk, forming a conjunction with the Moon. In some parts of southwestern China, a lunar occultation of Venus can be observed.
Moon age 2.4, Venus magnitude -4.0.
City Start Time End Time Guangzhou 19:37 19:59 Nanning 19:26 20:07 Guiyang 19:29 19:54 Kunming 19:18 20:05 Lhasa 18:55 19:54 Haikou 19:28 20:13 Kashgar 18:25 19:14 Hong Kong 19:37 20:01 Macau 19:35 20:03
As Earth’s natural satellite, the Moon constantly orbits the Earth with a period of about 29.5 days. From our perspective, it moves eastward relative to the background stars by about 12^\circ per day, or about 0.5^\circ per hour. This is almost equal to the Moon’s apparent diameter. Therefore, if the proper motion of the occulted planet is not considered, the maximum duration of a lunar occultation is about one hour. Of course, this refers to the case where the occulted star passes through the maximum diameter of the Moon. In most regions, the occultation is seen through shorter chords on either side, so the duration is relatively much shorter. This is similar to how the duration of a total solar eclipse is longer on the central line of the path of totality. We now know that lunar occultations follow the same principle as solar eclipses. Therefore, the region on Earth where an occultation can be observed is similar to an eclipse path, except that in most cases, the occulted star can be regarded as a point source, and the width of the occultation path is much larger than that of a total or annular solar eclipse—roughly half the width of the entire partial eclipse zone.
Let’s look at the crescent moon occulting Venus on the evening of May 16. The regions in China where this phenomenon is visible mainly include Xinjiang, Tibet, Yunnan, Guizhou, Guangxi, Guangdong, Hainan, as well as Hong Kong and Macau. In addition, most other regions can see a very close conjunction of Venus and the Moon. Like a solar eclipse, the sequence of visible regions for a lunar occultation is from west to east. In Kashgar, at the westernmost tip of Xinjiang, the occultation begins at 18:25 Beijing Time. The Moon’s altitude is about 65^\circ, which seems like good observation conditions. However, in reality, until the occultation ends at 19:14, the local sun will not have set. Observing such a daytime occultation is quite difficult. Looking at Hong Kong at the eastern end of the occultation zone, the occultation begins at 19:37. Although the Moon’s altitude is only 18^\circ, the sun has already set, so the observation conditions are quite good. When the occultation ends at 20:01, the Moon’s altitude will still be around 13^\circ.
Note: On the evening of December 1, 2008, a lunar occultation of Venus occurred, while Venus and Jupiter appeared next to the crescent moon. This beautiful celestial feast could be enjoyed worldwide during the first half of the night. Image credit and copyright: Johannes Schedler (Panther Observatory)
When the moon phase is a crescent, we can see the illuminated side is only a small part on the west, while the eastern part is the area facing away from the sun. Since the Moon moves from west to east, this lunar occultation of Venus will be "entering from the dark side, exiting from the bright side."
Observing the lunar occultation of Venus has high scientific value. We can use it to precisely locate the Moon and Venus, thereby studying their orbital patterns. For friends outside the occultation zone in China, this is also a good opportunity to appreciate the conjunction of Venus and the Moon. Taking the Beijing area as an example, around 19:30 that evening, the angular distance between the Moon and Venus will be at its closest, about 10^\prime. Moreover, the brightness of the crescent moon per unit area is even less than that of Venus. If the weather is clear, we can use a telescope or a telephoto lens to easily photograph them by choosing an appropriate exposure value.
May 26: Mercury at Greatest Western Elongation
Mercury orbits the Sun with a period of 88 days, and its orbit is inside the Earth’s orbit. Therefore, from our perspective, the angular distance between Mercury and the Sun never exceeds 28^\circ. Through the synodic period formula, we can calculate that Mercury appears on the east and west sides of the Sun with a period of 116 days. When the angular distance between it and the Sun reaches its maximum within a cycle, we call it the greatest eastern or western elongation. Since Mercury’s orbit around the Sun is an ellipse, in most cases, the angular distance between Mercury and the Sun does not reach 28^\circ. Of course, a larger angular distance does not necessarily mean better observation conditions. For observers in the Northern Hemisphere, if Mercury’s declination is lower than the Sun’s, even if the angular distance is large, Mercury’s altitude at sunrise or sunset will be very low, making it unsuitable for observation, while the opposite is true for the Southern Hemisphere.
During the greatest western elongation of Mercury on May 26, its angular distance from the Sun can reach 25^\circ, but its declination is about 10^\circ lower than the Sun’s, which directly affects the observation. Taking an area at about 40 degrees north latitude as an example, Mercury’s altitude in the eastern sky at sunrise is only 10^\circ, and its brightness is only magnitude 0.4, so the observation conditions are not good. If you want to observe Mercury, it is best to wait for the greatest western elongation on September 20, when the observation conditions will be much better.
Sun: Moves from Aries to Taurus.
Moon: Passes apogee on the 7th at 06:00, passes perigee on the 20th at 17:00. Phases: Last Quarter on the 6th at 12:15, New Moon on the 14th at 09:04, First Quarter on the 21st at 07:43, Full Moon on the 28th at 07:07.
Mercury: Morning star, difficult to observe. On the 11th at 08:00, Mercury is at station. On the 26th, greatest western elongation, altitude 13 degrees, magnitude 0.4.
Venus: Evening star, moves from Taurus into Gemini, in the northwestern sky at sunset. Altitude about 25 degrees, brightness -3.9 magnitude. On the 4th at 12:00, Venus in conjunction with Aldebaran, Venus is 6 degrees north of Aldebaran. On the 16th at 18:00, lunar occultation of Venus, Venus is 0.1 degrees south of the Moon.Mars: Moves prograde from Cancer to Leo. Located in the southwestern sky at sunset, brightness about 0.9 magnitude, visible in the first half of the night. On the 20th at 20:00, Mars in conjunction with the Moon, Mars is 5 degrees north of the Moon.
Jupiter: Moves prograde in Aquarius. Rises from the southeast at 02:20 AM, brightness about -2.2 magnitude. On the 10th at 02:00, Jupiter in conjunction with the Moon, Jupiter is 6 degrees south of the Moon.
Saturn: Moves retrograde in Virgo. High in the southeastern sky at sunset, moves to the southwestern sky in late May, brightness about 0.9 magnitude. On the 23rd at 13:00, Saturn in conjunction with the Moon, Saturn is 8 degrees south of the Moon.
Uranus: In Pisces. On the 10th at 09:00, Uranus in conjunction with the Moon, Uranus is 6 degrees south of the Moon.
Neptune: In Aquarius. Brightness 7.8 magnitude.
Asteroids: Asteroid 4 Vesta is in Leo, brightness decreasing from 7.3 magnitude at the beginning of the month to 7.7 magnitude at the end. About 90 degrees from the Sun. Asteroid 2 Pallas reaches opposition on May 15, brightness 8.8 magnitude. Asteroid 1 Ceres, brightness 7.9 magnitude. Asteroid 12 Victoria reaches opposition on May 11, brightness 9.2 magnitude.
Source: "2010 Astronomical Outlook", compiled by Baidu "wap astronomy" bar, reproduction must indicate the source.
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