April 2013 Celestial Calendar & Observing Notes c/o Dave Mitsky

[Big Dipper]

April 2013 Celestial Calendar & Observing Notes c/o Dave Mitsky

(calendar data also reproduced in our forum calendar).

*NB: Check out also the resources at the end of Dave's calendar for further reading/information*

All times unless otherwise noted are UT.

4/2 Mercury is at aphelion today

4/3 Last Quarter Moon occurs at 4:37

4/4 The Curtiss Cross, an X-shaped illumination effect located between the craters Parry and Gambart, is predicted to begin at 12:37

4/7 Neptune is 6 degrees south of the Moon at 1:00

4/8 Mercury is 7 degrees south of the Moon at 10:00

4/10 New Moon (lunation 1117) occurs at 9:35

4/12 Pluto is stationary at 19:00

4/14 Jupiter is 2 degrees north of the Moon at 18:00

4/15 The Moon is at apogee, subtending 29'30" from a distance of 404,862 kilometers (251,568 miles), at 22:00

4/17 The Lunar X (also known as the Werner or Purbach Cross), an X-shaped illumination effect involving various rims and ridges between the craters La Caille, Blanchinus, and Purbach, is predicted to begin at 23:57

4/18 Mars is in conjunction with the Sun at 0:00; First Quarter Moon occurs at 12:31

4/19 Mercury is 2 degrees south of Uranus at 21:00

4/22 Mercury is at its greatest heliocentric latitude south today; the peak of the Lyrid meteor shower (20 per hour) occurs at 11:00

4/25 The Moon is 0.004 degree north of the first-magnitude star Spica (Alpha Virginis), with an occultation visible from Madagascar, southern Africa, northern South America, the Caribbean, and southern Central America, at 0:00; Full Moon, known as the Egg or Grass Moon, occurs at 19:57; a partial lunar eclipse reaches its maximum at 20:07

4/26 Saturn is 4 degrees north of the Moon at 2:00

4/27 The Moon is at perigee, subtending 32'59" from a distance of 362,268 kilometers (225,103 miles), at 20:00

4/28 Saturn is at opposition (magnitude 0.1, apparent size 18.9") at 8:00

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

The first photograph of the Sun was taken on April 2, 1845. The Hubble Space Telescope was placed in orbit on April 25, 1990. The Compton Gamma Ray Observatory achieved orbit on April 7, 1991.

The Lyrid meteor shower peaks on the morning of April 22. A typical zenithal hourly rate is about 20 meteors per hour but occasional short outbursts have occurred.

The Moon is 20.2 days old and is located in Ophiuchus at 0:00 UT on April 1. It's at its greatest northern declination of +20.2 degrees on April 15 and its greatest southern declination of -20.2 degrees on April 1 and April 28. Latitudinal libration is at a maximum of +6.8 degrees on April 20 and a minimum of -6.8 degrees on April 5. Longitudinal libration is at a maximum of +5.1 degrees on April 8 and a minimum of -6.6 degrees on April 21. The waxing Moon occults Chi Virginis (magnitude 4.7) for most of North America on the night of April 23. A partial lunar eclipse that’s visible primarily from the eastern hemisphere begins at 19:54 UT and ends at 20:21 UT on April 25. Visit http://saberdoesthestars.wordpress.com/2011/07/05/saber-does-the-stars/ 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.

Brightness, apparent size, illumination, distance from the Earth in astronomical units, and location data for the planets and Pluto on April 1: Mercury (+0.2 magnitude, 7.5", 51% illuminated, 0.89 a.u., Aquarius), Venus (--------------, 100% illuminated, 1.72 a.u., Pisces), Mars (+1.2 magnitude, 3.9", 100% illuminated, 2.41 a.u., Pisces), Jupiter (-2.1 magnitude, 35.8", 99% illuminated, 5.51 a.u., Taurus), Saturn (+0.3 magnitude, 18.6", 100% illuminated, 8.93 a.u., Libra), Uranus (+5.9 magnitude, 3.4", 100% illuminated, 21.01 a.u. on April 16, Pisces), Neptune (+7.9 magnitude, 2.2", 100% illuminated, 30.60 a.u. on April 16, Aquarius), and Pluto (+14.1 magnitude, 0.1", 100% illuminated, 32.15 a.u. on April 16, Sagittarius).

Jupiter is located in the west and Saturn is in the east in the evening. Saturn is in the southeast at midnight. Mercury can be found in the east, Saturn in the southwest, Uranus in the east, and Neptune in the southeast in the morning sky.

At midmonth, Mercury can be seen during morning twilight, Jupiter sets at midnight, and Saturn is visible the entire night for observers at latitude 40 degrees north.

Mercury is farthest from the Sun on April 2. The waning crescent Moon lies seven degrees to the north of Mercury on April 8. Mercury passes two degrees south of Uranus on April 19. Observers in the southern hemisphere will have a better view of the speedy planet.

Venus and Mars are less than one degree apart on April 6 but, being less than three degrees from the Sun, are not visible. Venus may be visible extremely low in the west-northwest shortly after sunset by month’s end.

Mars is in conjunction with the Sun on April 18.

Jupiter’s reign is nearing its end. As April ends, the massive gas giant sets by 11:00 p.m. Jupiter moves almost four degrees northeastward from the first-magnitude star Aldebaran, during the course of the month. It forms an equilateral triangle with second-magnitude star Beta Tauri and the third-magnitude star Zeta Tauri towards the end of April. Jupiter lies two degrees north of the waxing crescent Moon on April 14. Two occultations (of Io beginning at 10:40 p.m. EDT and of Ganymede beginning at 12:02 a.m. EDT) and a transit (by Europa starting at 11:04 p.m. EDT) take place on the night of April 2. This means that Callisto will be the only Galilean satellite visible for a good part of the night. Browse http://skyandtelescope.com/observing/objects/planets/article_107_1.asp in order to determine transit times of Jupiter’s central meridian by the Great Red Spot. Data on the Galilean satellites is available at http://skytonight.com/observing/objects/javascript/3307071.html#

On the night of April 25, the Full Moon passes four degrees south of the Ringed Planet. Saturn’s disk subtends 19 arc seconds at its equator and 17 arc seconds from pole to pole when it reaches opposition on April 28. Saturn is 8.82 astronomical units or 73 light-minutes from the Earth at that time and the north side of Saturn’s ring plane is tilted 18.1 degrees with respect to the Earth. The planet shines at magnitude 0.1 and its rings span 43 by 13 arc seconds at opposition. Titan (magnitude 8.4) lies due north of Saturn on the nights of April 12 and April 28 and due south of the planet on the nights of April 4 and April 20. Saturn’s unusual moon Iapetus, which varies in brightness from magnitude 10.1 to magnitude 11.9, is located 2.5 arc minutes north of Saturn on the night of April 1. At that time, it shines at eleventh magnitude. Iapetus is at greatest eastern elongation on the night of April 21. For further information on Saturn’s satellites, browse http://www.skyandtelescope.com/observing/objects/javascript/3308506.html

Uranus and Neptune may be visible during morning twilight. Southern hemisphere observers will have a more favorable view of the two gas giants.

The dwarf planet Pluto is fairly high in the sky in northwestern Sagittarius during morning twilight.

For more on the planets and how to locate them, browse http://www.nakedeyeplanets.com/

Asteroid 4 Vesta shines at eighth magnitude as it heads eastward through Taurus and into Gemini this month. It passed north of M1 (the Crab Nebula) on the night of April 7 and in front of the faint but rich open cluster NGC 2158 for two hours on the evening of April 29. NGC 2158 is located approximately one quarter of a degree southwest of the bright open cluster M35 in Gemini.

During April, the bright comet C/2011 L4 (PanSTARRS) travels northward through the constellations of Andromeda and Cassiopeia. It passes two degrees to the west of the bright spiral galaxy M31 on the nights of April 4 and April 5. Updates on Comet PanSTARRS and a finder chart can be found at http://www.skyandtelescope.com/observing/highlights/185665152.html and on page 51 of the March issue of Sky & Telescope respectively. Visit http://cometchasing.skyhound.com/ for additional information on this comet and others visible this month.

A free star map for April can be downloaded at http://www.skymaps.com/downloads.html

The famous eclipsing variable star Algol (Beta Persei) is at a minimum, decreasing in magnitude from 2.1 to 3.4, on April 2, 5, 8, 11, 14, 17, 20, 23, 25, 28 (see page 51 of the April issue of Sky & Telescope for the eclipse times). For more on Algol, see http://stars.astro.illinois.edu/sow/Algol.html and http://www.solstation.com/stars2/algol3.htm

Seventy-five 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)

Notable carbon star for April: V Hydrae (Hydra)

One hundred deep-sky objects for April: NGC 4024, NGC 4027 (Corvus); NGC 3511, NGC 3513, NGC 3672, NGC 3887, NGC 3892, NGC 3955, NGC 3962, NGC 3981 (Crater); NGC 3091, NGC 3109, NGC 3145, NGC 3203, NGC 3242, NGC 3309, NGC 3585, NGC 3621, NGC 3717, NGC 3904, NGC 3936 (Hydra); M65, M66, M95, M96, M105, NGC 3098, NGC 3162, NGC 3177, NGC 3185, NGC 3190, NGC 3226, NGC 3227, NGC 3300, NGC 3346, NGC 3367, NGC 3377, NGC 3384, NGC 3389, NGC 3412, NGC 3437, NGC 3489, NGC 3495, NGC 3507, NGC 3521, NGC 3593, NGC 3607, NGC 3608, NGC 3626, NGC 3628, NGC 3630, NGC 3640, NGC 3646, NGC 3655, NGC 3681, NGC 3684, NGC 3686, NGC 3691, NGC 3810, NGC 3842, NGC 3872, NGC 3900, NGC 4008 (Leo); NGC 3245, NGC 3254, NGC 3277, NGC 3294, NGC 3344, NGC 3414, NGC 3432, NGC 3486, NGC 3504 (Leo Minor); NGC 2990, NGC 3044, NGC 3055, NGC 3115, NGC 3156, NGC 3166, NGC 3169, NGC 3246, NGC 3423 (Sextans); IC 750, M97, M108, M109, NGC 3079, NGC 3184, NGC 3198, NGC 3310, NGC 3359, NGC 3610, NGC 3665, NGC 3675, NGC 3738, NGC 3877, NGC 3898, NGC 3941, NGC 3953, NGC 3998, NGC 4026 (Ursa Major)

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

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

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

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*Suggestions for further reading/information:*

Check out the following two sites (both are primarily UK-based) - each of which contain excellent celestial guides for the month ahead:

Astronomical Calendar

Astronomy.co.uk (site includes a short video highlighting some of the main celestial events for the month ahead).