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April 2010 Celestial Calendar

Dave Mitsky

Note: All times in UTC (EST + 5)

Christiann Huygens (1629-1695) was born this month.

The Lyrid meteor shower peaks during the morning of April 22. A typical zenithal hourly rate is about 20 meteors per hour. However, outbursts of up to 90 meteors per hour have occurred in some years.

The zodiacal light can be seen from a dark site in the early evening during the first week of April.

The Moon is 16.1 days old and is located in Libra at 0:00 UT on April 1. It's at its greatest southern declination of -25.3 degrees on April 4 and its greatest northern declinations of +25.2 degrees on April 18. Latitudinal libration is at a maximum of +6.6 degrees on April 26 and a minimum of -6.5 degrees on April 13. Longitudinal libration is at a maximum of +6.6 degrees on April 2 and +5.7 degrees on April 30 and a minimum of -5.2 degrees on April 26. Visit http://www.astronomyblogs.com/member/saberscorpx/?xjMsgID=50821 for tips on spotting extreme crescent Moons. Times and dates for the lunar light rays predicted to occur this month are available at http://www.lunar-occultations.com/rlo/rays/rays.htm

The Sun is located in Pisces on April 1. The first photograph of the Sun was taken on April 2, 1845.

Brightness, apparent size, illumination, distance from the Earth in astronomical units, and location data for the planets and Pluto on April 1: Mercury (-0.9 magnitude, 6.2", 70% illuminated, 1.09 a.u., Pisces), Venus (-3.9 magnitude, 10.5", 95% illuminated, 1.59 a.u., Aries), Mars (+0.2 magnitude, 9.2", 92% illuminated, 1.01 a.u., Cancer), Jupiter (-2.0 magnitude, 33.5", 100% illuminated, 5.88 a.u., Aquarius), Saturn (+0.6 magnitude, 19.5", 100% illuminated, 8.52 a.u., Virgo), Uranus (+5.9 magnitude, 3.4", 100% illuminated, 21.06 a.u., Pisces), Neptune (+7.9 magnitude, 2.2", 100% illuminated, 30.74 a.u., Aquarius), and Pluto (+14.0 magnitude, 0.1", 100% illuminated, 31.69 a.u., Sagittarius).

During April, Mercury and Venus are located in the west, Mars in the southwest, and Saturn is in the southeast in the evening. Mars is in the west and Saturn in the south at midnight. Jupiter and Uranus can be found in the east and Saturn in the west in the morning sky.

Mercury undergoes its best evening apparition of 2010 for observers in the mid-northern latitudes. It is most prominent during the first ten days of the month and is at least ten degrees above the horizon from April 1 to April 15. However, the planet fades in brightness from magnitude -0.9 to magnitude 1.4 during that time. When Mercury reaches greatest eastern elongation on April 8, it is 40% illuminated and shines at magnitude 0.1. Mercury, Venus, and a 1.5-day-old Moon appear together low in the west-northwest on April 15. Mercury is less than two degrees below the very thin crescent Moon on that date.

This month Venus lies low in the west-northwest but shines brightly at magnitude -3.9. Venus and Mercury are three degrees apart on April 4, the first so-called quasi-conjunction (i.e., the approach of two celestial bodies within five degrees without sharing the same right ascension or ecliptic longitude) between bright planets in four years. The two planets are within four degrees of each other during the first ten days of April. This distance increases to six degrees by April 14 and to seven degrees by April 15. On April 16, the crescent Moon passes four degrees to the north of Venus. The Pleiades (M45) and Venus are approximately 3.5 degrees apart on the evenings of April 23 and April 24.

Mars is still prominent but is fading fast as Earth continues to pull away from the Red Planet. It decreases by half a magnitude in brightness and shrinks in apparent size by two arc seconds by the end of the month when it shines at magnitude 0.7 and subtends only 7 arc seconds. Mars and the Beehive Cluster (M44) are within two degrees of each other for a week starting on April 13. From April 16 to April 18, Mars is only one degree north of the center of the cluster.

Jupiter rises about an hour before the Sun in early April and about two hours before sunrise by the end of the month. The waning crescent Moon is about five degrees to Jupiter's north on April 11. Click on http://skyandtelescope.com/observing/objects/planets/article_107_1.asp to determine transits of the central meridian by the Great Red Spot. Data on the Galilean satellites is available at http://www.skyandtelescope.com/observing/objects/javascript/3307071.html

As Saturn retrogrades through Virgo, Saturn shines brighter than the constellation's lucida, Spica (Alpha Virginis). Saturn's disk subtends 19 arc seconds and its rings 44 arc seconds at mid-month. The ring tilt angle is two degrees at that time. Titan lies to the west of Saturn during the first week of the month. It reaches greatest eastern elongation on April 11. Titan is positioned to the east of the Ringed Planet from April 23 to month's end. Saturn's unusual moon Iapetus brightens noticeably during the course of April. It's located nine arc minutes east of Saturn and shines at only twelfth-magnitude in early April. Iapetus is just 1.4 arc minutes due south of the planet on April 17. By the end of April, it has moved well to the west of the planet. Iapetus lies to the southeast of Titan on April 11 and to the south of Titan on April 20. For further information on Saturn's satellites, browse http://www.skyandtelescope.com/observing/objects/javascript/3308506.html

Uranus is not readily observable this month.

Neptune lies approximately midway between the fifth-magnitude star Mu Capricorni and the fifth-magnitude star 38 Aquarii on April 30, close to the position that Neptune occupied when it was discovered by Johann Galle in 1846.

The dwarf planet Pluto is located a bit more than one degree to the southeast of the bright open cluster M18 in northwestern Sagittarius.

Comet C/2009 O2 (Catalina) shines at ninth-magnitude as it travels southeastward through Taurus this month. It passes very close to the fifth-magnitude star 41 Tauri on April 9 and through the large open cluster NGC 1647 on April 16 and April 17. Comet 81P/Wild can be found within several degrees of the fourth-magnitude star Iota Virginis. Visit http://cometchasing.skyhound.com/ for additional information on these comets.

Asteroid 4 Vesta passes southeastward through Leo. It lies a bit more than one degree southeast of the third-magnitude star Algenubi (Epsilon Leonis) during early April. By month's end, it's located about three degrees from Epsilon Leonis. Asteroid 9 Metis is at opposition on April 11.

The famous eclipsing variable star Algol (Beta Persei) is at a minimum, decreasing in magnitude from 2.1 to 3.4, on April 3, 6, 9, 12, 15, 17, 20, 23, 26, and 29. For more on Algol, see http://stars.astro.illinois.edu/sow/Algol.html and http://www.solstation.com/stars2/algol3.htm

Binary and Multiple Stars for April

h4481 (Corvus); Aitken 1774, Gamma Crateris, Jacob 16, Struve 3072, h4456, Burnham 1078 (Crater); h4311, Burnham 219, N Hydrae, h4455, h4465 (Hydra); 31 Leonis, Alpha Leonis (Regulus), h2520, Struve 1417, 39 Leonis, Struve 1421, Gamma Leonis (Algieba), Otto Struve 216, 45 Leonis, Struve 1442, Struve 1447, 49 Leonis, Struve 1482, 54 Leonis, Struve 1506, Chi Leonis, 65 Leonis, Struve 1521, Struve 1527, Struve 1529, Iota Leonis, 81 Leonis, 83 Leonis, Tau Leonis, 88 Leonis, 90 Leonis, Struve 1565, Struve 1566, 93 Leonis, h1201, S Leonis (Leo); h2517, Struve 1405, Struve 1432, 33 Leo Minoris, Struve 1459, 40 Leo Minoris, Struve 1492 (Leo Minor); Struve 1401, Struve 1441, Struve 1456, Struve 1464, 35 Sextantis, 40 Sextantis, 41 Sextantis (Sextans); Struve 1402, Struve 1415, Struve 1427, Struve 1462, Struve 1486, Struve 1495, Struve 1510, Struve 1520, Xi Ursae Majoris, Nu Ursae Majoris, Struve 1541, 57 Ursae Majoris, Struve 1544, Struve 1553, Struve 1561, Struve 1563, 65 Ursae Majoris, Otto Struve 241 (Ursa Major)

Challenge binary star for April: Gamma Sextantis

Notable carbon star for April: V Hydrae (Hydra)

Challenge deep-sky object for April: Leo I (Leo)

Top ten deep-sky objects for April: M65, M66, M95, M96, M97, M105, M108, NGC 3115, NGC 3242, NGC 3628

Top ten binocular deep-sky objects for April: M65, M66, M95, M96, M97, M105, M108, M109, NGC 3115, NGC 3242

The objects listed above are located between 10:00 and 12:00 hours of right ascension.