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April 2011 Celestial Calendar & Observing Notes c/o Dave Mitsky

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April 2011 Celestial Calendar & Observing Notes courtesy of Dave Mitsky (calendar data also reproduced in our forum calendar).

All times, unless otherwise noted, are UT.

4/2 The Moon is at apogee, subtending 29 arc minutes from a distance of 406,656 kilometers (252,684 miles), at 9:00

4/3 New Moon (lunation 1092) occurs at 14:32

4/4 Saturn (magnitude 0.4, apparent size 19.3") is at opposition at 0:00

4/6 Jupiter is in conjunction with the Sun at 15:00

4/7 The Moon is 1.9 degrees south of the bright open cluster M45 (the Pleiades) in Taurus at 11:00

4/9 Pluto is stationary at 7:00; Mercury is in inferior conjunction with the Sun at 20:00

4/10 The Moon is 1.5 degrees south of the bright open cluster M35 in Gemini at 1:00; 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 18:19

4/11 First Quarter Moon occurs at 12:05

4/17 The Moon is at perigee, subtending 32 arc minutes from a distance of 358,090 kilometers (222,507 miles), at 6:00; Saturn is 8 degrees north of the Moon at 8:00

4/18 Venus is at aphelion today; Mercury is at the descending node today; Full Moon, known as the Egg or Grass Moon, occurs at 2:44

4/19 Mercury is 0.8 degree north of Mars at 9:00

4/22 Mercury is stationary at 5:00; Venus is 0.9 degree south of Uranus at 18:00; the peak of the Lyrid meteor shower (20 per hour) occurs at 23:00

4/25 Last Quarter Moon occurs at 2:47

4/26 The Curtiss Cross, an X-shaped illumination effect located between the craters Parry and Gambart, is predicted to begin at 18:39

4/27 Neptune is 6 degrees south of the Moon at 10:00

4/29 Mercury is at aphelion today; asteroid 3 Juno is stationary at 16:00; the Moon is at apogee, subtending 29 arc minutes from a distance of 406,039 kilometers (252,301 miles), at 18:01

4/30 Uranus is 6 degrees south of the Moon at 4:00; Venus is 7 degrees south of the Moon at 23:00

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. However, outbursts of up to 90 meteors per hour have occurred in some years on a 12 -year cycle. Unfortunately, moonlight from a waning gibbous Moon will compromise the Lyrids this year.

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

The Moon is 27.2 days old and is located in Aquarius at 0:00 UT on April 1. It's at its greatest northern declination of +23.6 degrees on April 8 and its greatest southern declination of -23.4 degrees on April 21. Latitudinal libration is at a maximum of +6.6 degrees on April 16 and a minimum of -6.6 degrees on April 2 and -6.7 degrees on April 29. Longitudinal libration is at a maximum of +7.2 degrees on April 22 and a minimum of -7.6 degrees on April 11. Large tides occur on April 17 through April 20. The Moon will occult Kappa (magnitude 4.3) and/or Upsilon Tauri (magnitude 4.3) on the evening of April 7 for observers in western North America. On the evening of April 10, Zeta Geminorum (magnitude 3.8) will be occulted for observers in eastern North America. Click on IOTA Document for additional information on these events. Visit Extreme Lunar Crescent Data [L1092-1104] | 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 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, 9.7", 12% illuminated, 0.69 a.u., Pisces), Venus (-3.9 magnitude, 13.2", 80% illuminated, 1.26 a.u., Aquarius), Mars (+1.2 magnitude, 4.0", 99% illuminated, 2.35 a.u., Pisces), Jupiter (-2.1 magnitude, 33.2", 100% illuminated, 5.94 a.u., Pisces), Saturn (+0.4 magnitude, 19.3", 100% illuminated, 8.62 a.u., Virgo), Uranus (+5.9 magnitude, 3.4", 100% illuminated, 21.07 a.u., Pisces), Neptune (+7.9 magnitude, 2.2", 100% illuminated, 30.76 a.u., Aquarius), and Pluto (+14.0 magnitude, 0.1", 100% illuminated, 31.93 a.u., Sagittarius).

Mercury is located in the west (as April begins) and Saturn is in the southeast in the evening. Saturn is in the south at midnight. Mercury (as April ends), Venus, Jupiter and Uranus can be found in the east, Neptune in the southeast, and Saturn in the west in the morning sky.

Mercury can be seen at evening twilight at the start of the month and at morning twilight at the end of the month, Venus rises at 5:00 a.m. EDT at midmonth, Mars and Jupiter are visible at morning twilight at the end of the month, and Saturn is visible the entire night for observers at latitude 40 degrees north.

On the morning of April 30, a waxing crescent Moon, Venus, Mercury, Mars, and Jupiter are clustered together low in the eastern sky. Use binoculars for a better view.

Mercury is visible in the evening at the beginning and in the morning at month’s end. It is in conjunction with the Sun on April 9. Mercury is situated less than a degree from Mars on the morning of April 19 and less than four degrees from Venus at dawn on April 30.

Venus rises by 5:30 a.m. local daylight time on April 1. The brilliant planet is less than a degree north of Uranus on April 22. On April 30, it rises an hour before the Sun and is located seven degrees south of a thin crescent Moon.

Mars is visible by the end of April. The Red Planet is just half a degree north-northwest of Jupiter on the morning of April 30.

Jupiter is not readily observable this month. It is only one degree above the eastern horizon one half an hour before sunrise on April 30.

As Saturn glides westward through Virgo, it shines brighter than the constellation’s lucida, the first-magnitude star Spica (Alpha Virginis). When it is at opposition on April 3, Saturn lies approximately halfway between the third-magnitude star Gamma Virginis and the fourth-magnitude star Theta Virginis. Saturn’s disk subtends 19 arc seconds and its rings 44 arc seconds in early April. The ring tilt angle is nine degrees at that time. Saturn’s retrograde motion places it two degrees from Gamma Virginis by the end of April. Eighth-magnitude Titan lies due south of Saturn on April 1 and due north of the planet on April 9 and April 25. On April 3, Titan is positioned to 2.6 arc seconds west of the Ringed Planet. Saturn’s unusual moon Iapetus is located 6.4 arc minutes west-northwest of Saturn on the night of April 3 and 1.8 arc minutes north of the planet on the night of April 12. For further information on Saturn’s satellites, browse Saturn's Moons Javascript Utility - Interactive Observing Tools - SkyandTelescope.com

Uranus is not easily observable this month.

Neptune is 14 arc seconds due south of the fifth-magnitude star 38 Aquarii on April 27.

The dwarf planet Pluto is located in northwestern Sagittarius.

There are no noteworthy comets to be seen this month.

Asteroid 3 Juno shines at magnitude 9.5 as it passes northwestward through Leo during April. It lies two degrees northwest of the fourth-magnitude star Sigma Leonis on April 1 and a bit more than one degree to the northeast of the fifth-magnitude star Chi Leonis on April 11.

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

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