Skywatchers’ Guide for April 2010

Skywatchers’ Guide for April 2010

HIGHLIGHTS: Saturn, in the eastern evening sky, is large and bright and now high enough in the evening sky for convenient evening telescopic viewing. The rings of Saturn appear very thin, as we view them nearly edge-on from Earth. Mars is high up overhead in the evening as well, but appears too small for quality, sharp views of surface features in small, amateur telescopes. Brilliant Venus and elusive Mercury have a fairly close grouping in the bright western evening twilight, 30-40 minutes after sunset. Bright Jupiter is visible in the east-southeastern area of the morning twilight sky.

PLANETS

Saturn and the constellation Leo in the eastern evening sky on April 1 at around 7:45 p.m. This sky chart is most useful for the entire United States, southern Canada and northern Mexico. Venus and Mercury in the evening twilight sky on April 2 at around 7:30 p.m. facing west, about 45 minutes after sunset. This sky chart is most useful for the entire United States, southern Canada and northern Mexico. Mars with the Moon in the evening sky looking overhead on April 21 at 8 p.m. This sky chart is most useful for the entire United States, southern Canada and northern Mexico.

April 2010 is a great time to see Saturn and its ring system, as Saturn is conveniently high up in the evening sky. The rings of Saturn appear very thin, as we view them nearly edge-on from Earth. Saturn appears as a first magnitude star-like object (at around magnitude 0.6 and 19 arc seconds across) during April. Saturn was at opposition on March 21, opposite from the Sun in the sky and rising at sunset. Day by day Saturn rises earlier in our sky and moves higher overhead in the convenient evening hours (well placed for telescopic viewing). The best views of any planet should be when it is highest in the sky, but viewing is dependent on atmospheric stability and conditions, and of course, the quality and size of the telescope used. Large, high quality amateur telescopes in good “seeing” (stable atmospheric conditions) will best reveal any features on a planet’s disk. Saturn is located below Leo the Lion in the constellation Virgo the Virgin. The 11-day-old waxing gibbous Moon is found below and nearest Saturn in our sky on Sunday evening, April 25.

The brilliant planet Venus at the start of April lies 16 degrees above the western horizon in the bright evening twilight, 30 minutes after sunset. Venus slowly gains altitude out of the glare of the Sun and sets a little later each evening during the entire month.  Venus appears in a gibbous phase and appears to pass closest to the Pleiades on April 24 and the Hyades on April 30.

Mercury has its best apparition of the year this April. It starts the month at -0.8 magnitude 7 degrees above the western horizon 45 minutes after sunset. It will be visible just to the right and slightly below Venus, reaching a minimum separation of 3 degrees on April 3.  For the next week Mercury will then continue to lose brightness but gain altitude and move away from the glare of the Sun. It reaches greatest elongation (separation from the Sun) on April 8, staying up 1.5 hours after sunset. It then turns back toward the Sun, and will not be visible by the last week of April. On the evening of Thursday April 15, the razor thin Moon will lie just above much fainter Mercury (at magnitude 1.5).

Mars is now very high in the sky at sunset at an altitude of about 70 degrees. It is well past opposition and continues to diminish in apparent size and brightness, dropping from magnitude 0.2 to 0.7 over the month. A 7-day-old first quarter moon will lie close to Mars on April 21.  Mars, in the constellation of Cancer the Crab, will pass only about a degree from the Beehive Cluster on April 16.  Mars sets earlier each night, at about 3 a.m. on April 1, and at around 1:45 a.m. on April 30.

Bright Jupiter gains altitude each morning this April but is still low above the eastern horizon. By the end of April the giant planet is easily seen almost 12 degrees above the east-southeastern horizon one hour before sunrise (from the southern United States). Jupiter is located in the constellation of Capricornus, the Sea Goat, and is the brightest star like object that is well up in the morning twilight. The waning crescent Moon appears nearest in our sky and above (west of) Jupiter on the morning of Sunday April 11: Jupiter will lie over 5 degrees from the Moon’s edge as seen from the Desert Southwest that morning.

Visitors to Flandrau’s 16-inch observatory telescope should note that of the planets only Saturn is visible in the telescope during public hours. However other celestial objects, including the Great Orion Nebula will be shown in the telescope, weather permitting. Flandrau’s main exhibit hall and planetarium is now open Friday through Sunday afternoon (not open Sunday night) and our observatory telescope remains open for viewing during public hours from 7-10 p.m., weather permitting, Wednesday through Saturday nights (excluding select holidays).

Finally, remember that in spotting planets there is a general rule: “stars twinkle, planets don’t”. This is because stars are point sources of light; therefore starlight is easily disturbed and shifted by air currents in the Earth’s atmosphere. However when looking at Mercury or Mars this month, note that they may appear to twinkle somewhat; This twinkling is of a slower nature than that of the bright stars.

Zodiacal Light Visible

April is an excellent month, and Arizona is a superb place, to look at the Zodiacal Light in the western evening sky, starting 75 minutes after sunset. The Zodiacal Light is sunlight reflecting off of meteoritic dust in our solar system. Because this dust lies along the plane of the solar system, we see its faint glow as a cone of light along the constellations of the Zodiac. Often confused with light pollution or twilight, the Zodiacal Light must be seen on clear moonless nights, in dark locations far away from city lights. In April look for the faint colorless cone shaped glow of the Zodiacal Light to reach high up from the western horizon engulfing the Pleiades, or ‘Seven Sisters’ star cluster.

APRIL EVENING STARS

The western sky in early April at 9:30 p.m and in mid-April at around 8:30 p.m. (sky shown without planets).The western sky in early April at 9:30 p.m and in mid-April at around 8:30 p.m. (sky shown without planets). The northern sky is shown in early April at 9 p.m and in mid-April at around 8 p.m. Find Polaris, the North Star off the pointer stars of the Big Dipper. The east northeastern sky is shown in early April at 9 p.m. and in mid-April at around 8 p.m. as seen from the southern U.S. ‘Arc to Arcturus’ and then ’speed on to Spica’ off the handle of the Big Dipper.

The bright stars of winter are still prominent in the evening April sky, but set in the western half of the sky early. Look in the west 1 hour after sunset for Orion, the Hunter, and his shimmering belt of “three stars in a row” to find other sights in the winter sky. Orange Betelgeuse, the shoulder of Orion the Hunter, shines upper left of Orion’s 3 glittering belt stars and blue white Rigel shines below. The Gemini Twins, the bright stars Castor and slightly brighter Pollux, twinkle left of Orion. Castor will be above Pollux. Take Orion’s belt and point down and left to Sirius, the brightest star in all the heavens. Sirius is the nose of the Greater Dog, Canis Major, a companion to Orion in the heavens. Later in the evening, Orion and his winter companions will set in the western sky. Orion’s belt will then point left to Sirius when in the western sky. Betelgeuse at that time can be found directly above Orion’s belt.

The Big Dipper is easy to find this April (and every April) in the northeast evening sky. Look for the Big Dipper high in the northeast 1-2 hours after sunset. Take the two ends stars off of the bowl (the Pointer stars Dubhe and Merak) and point to Polaris, the North or Pole Star. Polaris is a star of ordinary brightness, and marks the end of the handle of the Little Dipper. Polaris is a direct indicator of latitude and so is always found the number of degrees above the northern horizon equal to an observer’s latitude. In Tucson look for Polaris about 30 degrees (or 3 fists) above the northern horizon. Polaris stays put in the sky, so to the eye it doesn’t appear to move. This is because Earth’s axis is pointed toward Polaris in space.

The Big Dipper is an amazing signpost in the heavens, useful in finding many notable sights in the sky. The two stars forming the outside end of the Big Dipper’s bowl — the part opposite from the handle — are called “the Pointers.” A line drawn through them points quite near the North Star, Polaris. Polaris closely marks the north celestial pole, and hence appears not to move in the sky to the unaided eye. Polaris is also the end of the handle of the Little Dipper, whose other name is Ursa Minor, the Little Bear. Continue straight down from Polaris to the horizon to find true north. Polaris always remains at almost exactly the same point over the Northern Hemisphere landscape, day and night, and is always there to mark almost exactly due north. Polaris is not a very bright star, but it’s in a dim part of the sky in where there’s nothing else to confuse it. Come back to the Big Dipper and follow the curve of the Dipper’s handle back across the sky by about two handle-lengths and you’ll see the brightest star of spring, the bright yellow-white star Arcturus. Continue down from Arcturus to “spike” or speed onto the blue star of spring, Spica.

The Milky Way Prominent in the Morning!

The Milky Way, the galaxy of stars, gas, and dust in which our solar system resides, is prominent all summer long, but is especially prominent in the April morning sky after 2 a.m. To see it, you’ll need to get away from city lights to a dark location, and look on a night when there’s not much interference from the Moon. The Milky Way will appear as a “cloudy” band clear across the sky. High power binoculars and telescopes reveal the Milky Way to be clouds of stars, millions of them, with attendant star clusters and gas clouds making up some of the “fuzzier” spots you’ll see.

The Lyrid Meteor Shower
The relatively minor shower Lyrid shower peaks this year during the hours before dawn on April 21-22. The April Lyrids are considered a major shower, though are usually unimpressive to novice sky gazers. This year the shower’s peak on the morning of April 22 should have prime viewing due to the lack of interference from the razor thin waning crescent Moon, 2 days before new. This year the best views of the Lyrids should be obtained after midnight and until the start of morning twilight. Usually, up to 10 fast, bluish meteors per hour can be seen overhead in the hours after midnight and before sunrise from a dark Arizona sky. On rare occasions the shower may outburst, with a hundred or more faint shooting stars visible. To see the shower simply look up in a lawn chair towards the bright summer triangle of the bright stars Altair, Deneb and Vega after midnight. As with nearly all meteor showers, it is not necessary to look at the radiant (where the meteors appear to originate from) to best see the shower. Meteors can appear almost anywhere in the sky.

MOON PHASES

The April last quarter Moon occurs on Monday morning April 5. The April 2010 new moon will occur on Tuesday, April 13. The April first quarter Moon will occur on Wednesday evening, April 21, when it will appear to lie closest to the Moon this month. The April “Full Pink Moon” rises on the evening of Thursday, April 27 and sets on the morning of Friday, April 28.  Please note: These are the moon phases for mountain standard time in Arizona, not the moon phases listed on calendars which are often for Universal Time in Greenwich, England.

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