April 2012 Celestial Calendar & Observing Notes c/o Dave Mitsky

[Big Dipper]

April 2012 Celestial Calendar & Observing Notes courtesy of 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.

4/3 Mercury is stationary at 6:00; Venus is 0.5 degree south of the bright open cluster M45 (the Pleiades) in Taurus at 14:00

4/4 Mercury is at the descending node today; Mars is 9 degrees north of the Moon at 3:00

4/6 Full Moon, known as the Egg or Grass Moon, occurs at 19:19

4/7 The Moon is 1.5 degrees south of the first-magnitude star Spica (Alpha Virginis) at 7:00; Saturn is 6 degrees north of the Moon at 14:00; the Moon is at perigee, subtending 32' from a distance of 358,314 kilometers (222,646 miles), at 17:00

4/10 Asteroid 4 Vesta is in conjunction with the Sun at 0:00; Pluto is stationary at 15:00

4/11 Venus is at its greatest heliocentric latitude north today

4/13 Last Quarter Moon occurs at 10:50

4/15 Mercury is at aphelion today; the Curtiss Cross, an X-shaped illumination effect located between the craters Parry and Gambart, is predicted to begin at 4:19; Mars is stationary at 12:00; Saturn (magnitude 0.2, apparent size 19.1") is at opposition at 18:00

4/16 Neptune is 6 degrees south of the Moon at 15:00

4/17 Venus is 10 degrees north of the first-magnitude star Aldebaran (Alpha Tauri) at 1:00

4/18 Mercury is at greatest western elongation (27 degrees) at 17:00

4/19 Mercury is 8 degrees south of the Moon at 2:00; Uranus is 6 degrees south of the Moon at 8:00

4/21 New Moon (lunation 1105) occurs at 7:18

4/22 Mercury is 2 degrees south of Uranus at 2:00; the peak of the Lyrid meteor shower (20 per hour) occurs at 5:00; the Moon is at apogee, subtending 29' from a distance of 406,419 kilometers (252,537 miles), at 14:00; Jupiter is 2 degrees south of the Moon at 19:00

4/25 Venus is 6 degrees north of the Moon at 2:00

4/26 Asteroid 1 Ceres is in conjunction with the Sun at 14:00

4/28 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 14:55

4/29 First Quarter Moon occurs at 9:57

4/30 Venus is at its greatest illuminated extent at 8:00

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

The Hubble Space Telescope was placed in orbit on April 25, 1990.

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

The zodiacal light can be seen from a dark site in the early evening from April 10 to April 24.

The Moon is 9.4 days old and is located in Gemini at 0:00 UT on April 1. It's at its greatest northern declination of +21.8 degrees on April 25 and its greatest southern declination of -21.8 degrees on April 10. Latitudinal libration is at a maximum of +6.6 degrees on April 4 and a minimum of -6.7 degrees on April 16. Longitudinal libration is at a maximum of +6.9 degrees on April 14 and a minimum of -7.8 degrees on April 1 and -8.0 degrees on April 29. Large tides occur on April 6 through April 9. Visit Saber Does The Stars saberdoesthestars for tips on spotting extreme crescent Moons. Times and dates for the lunar light rays predicted to occur this month are available at Lunar Sunrise/Sunset Crater Rays

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 (+2.1 magnitude, 10.7", 13% illuminated, 0.63 a.u., Pisces), Venus (-4.5 magnitude, 24.8", 48% illuminated, 0.67 a.u., Taurus), Mars (-0.7 magnitude, 12.6", 97% illuminated, 0.75 a.u., Leo), Jupiter (-2.1 magnitude, 33.9", 100% illuminated, 5.81 a.u., Aries), Saturn (+0.3 magnitude, 19.0", 100% illuminated, 8.75 a.u., Virgo), Uranus (+5.9 magnitude, 3.4", 100% illuminated, 21.06 a.u., Pisces), Neptune (+7.9 magnitude, 2.2", 100% illuminated, 30.76 a.u., Aquarius), and Pluto (+14.1 magnitude, 0.1", 100% illuminated, 32.15 a.u., Sagittarius).

Venus is located in the west, Mars in the southeast, Jupiter in the west, and Saturn is in the east in the evening. Mars is in the southwest and Saturn is in the south 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.

Mercury can be seen during morning twilight, Venus sets at midnight, Mars transits at 10:00 p.m. local time and sets at 5:00 a.m. local time, Jupiter sets at 9:00 p.m. local time, and Saturn is visible the entire night for observers at latitude 40 degrees north.

Mercury reaches aphelion on April 15 and greatest eastern elongation three days later but is a difficult target for northern hemisphere observers this month due to the angle of the ecliptic.

Venus reaches its peak evening altitude of its eight year cycle in April. The brilliant planet pays the bright open cluster M45 (the Pleiades) a visit early this month. Venus is 0.6 degree south of the fourth-magnitude Pleiad Electra (17 Tauri) on April 2 and 0.3 degree south of the fourth-magnitude Pleiad Atlas (27 Tauri) on April 3. The planet lies approximately one degree from center of the Pleiades for a night before and after those dates. Venus is located three degrees from the second-magnitude star Beta Tauri by the end of the month. At that time, a 27% illuminated crescent Venus shines at magnitude -4.7 and subtends 37 arc seconds. Venus increases in apparent size by almost 50% this month, while growing steadily smaller in illuminated extent. For more on the 2012 apparition of Venus, see Venus

Mars achieves its maximum northern declination (12°53') for 2012 on April 5. On April 10, its apparent brightness drops below magnitude -0.5. The Red Planet ends its retrograde motion on April 15. Mars decreases in apparent size from 12.6 to 10.0 arc seconds and declines in magnitude from -0.7 to -0.1 this month. The dark surface feature known as Syrtis Major is near the central meridian at 11:00 p.m. EDT on April 13. An article with tips on observing Mars appears on pages 50 and 51 of the April issue of Sky & Telescope. Additional information can be found at Mars and Mars 2011/2012

Jupiter lies very low in the western sky in early April. On April 15, it’s just five degrees above the horizon an hour after the sun sets. The giant planet and a waxing crescent Moon are two degrees apart on April 22. By the end of the month, Jupiter disappears into the glare of the Sun.

Saturn shines almost a magnitude brighter than Virgo’s lucida, the first-magnitude star Spica (Alpha Virginis). Saturn is positioned five degrees northeast of Spica for the entire month. Saturn’s disk subtends 19 arc seconds and its rings 43 arc seconds when it reaches opposition on April 15. The ring tilt angle is 13.7 degrees and the planet is 8.72 astronomical units or 73 light-minutes from the Earth at that time. Eighth-magnitude Titan lies due north of Saturn on April 10 and April 26 and due south of the planet on April 2 and April 18. Saturn’s unusual moon Iapetus is located two arc minutes from Saturn on the night of April 6 and nine arc minutes from the planet at greatest western elongation on the night of April 26. For further information on Saturn’s satellites, browse

Saturn's Moons Javascript Utility - Interactive Observing Tools - SkyandTelescope.com

It may be possible to observe Uranus and Neptune just before dawn. Uranus appears lower in the sky, some six degrees above the horizon 45 minutes prior to sunrise at the end of April.

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 The Naked Eye Planets in the Night Sky (and how to identify them)

The main belt asteroid 6 Hebe continues on a northwest course through central Leo, eventually passing within 1.5 degrees of the beautiful second-magnitude binary star Algieba (Gamma Leonis). Hebe begins to retrograde on April 21. Asteroid 5 Astraea travels northwestward through southern Leo during April, while Asteroid 8 Flora departs Virgo and enters southeastern Leo. All three asteroids shine at tenth magnitude. Finder charts for 5 Astraea, 6 Hebe, and 8 Flora appear on pages 52 and 53 of the April issue of Sky & Telescope.

During April, comet C/2009 P1 (Garradd) passes southwestward through Ursa Major and into Lynx. It lies two degrees to the west of the ninth-magnitude spiral galaxy NGC 2841 on April 9. The fading comet passes between Iota and Kappa Ursae Majoris on April 13. A finder chart is available on page 60 of the March issue of Sky & Telescope. Visit Comet Chasing for additional information on this comet and others visible in April.

A free star map for April can be downloaded at Skymaps.com - Publication Quality Sky Maps & Star Charts

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, 18, 20, 23, 26, and 29 (see page 53 of the April issue of Sky & Telescope for the eclipse times). It will be at minimum brightness for approximately an hour before and after 10:44 p.m. EDT on the night of April 17 (April 18 in UT). There will not be another opportunity to see Algol at minimum in the evening sky from North America until next August. For more on Algol, see Algol and Algol / Beta Persei 3

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).