April 2009
Skywatchers’ Guide for April 2008
HIGHLIGHTS: Saturn, in the eastern evening sky, is conveniently high up in the sky for evening telescopic viewing. The rings of Saturn appear very thin, as we view them nearly edge-on from Earth. Brilliant Venus, now emerging in the morning sky, is covered or ‘occulted’ by the Moon on the morning of April 22, a rare and spectacular event. Three planets, Venus, Mars and Jupiter are widely spaced in the east-southeastern area of the morning twilight sky.
PLANETS
 The eastern evening sky on April 6 at around 7:45 p.m. This sky chart is most useful for the entire United States, southern Canada and northern Mexico.  The evening sky on April 21 at around 8 p.m. facing west. |
April 2009 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 zero magnitude star-like object (at around magnitude 0.5 and 19.5 arc seconds across) during April. Saturn was at opposition on March 8, it was 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 in the constellation Leo the Lion, well below and east of its bright star Regulus, which is the bottom of the star pattern called the ‘sickle’ of Leo. The 12-day-old waxing gibbous Moon is found below and nearest Saturn in our sky on Monday evening, April 6.
The brilliant planet Venus starts April just 2.5 degrees above the eastern horizon in the bright morning twilight, 30 minutes before sunrise. However, Venus quickly gains altitude out of the glare of the Sun and rises higher, earlier during the entire month. As it does so its narrow crescent phase thickens and becomes smaller as Venus also moves farther away from Earth (the opposite of its phase changes and visibility in March). Its crescent phase will be a spectacular sight in a telescope and may even be spotted in good quality binoculars (especially during the first half of April). By the last week of April Venus is over 11 degrees above the eastern horizon about 45 minutes before sunrise and will then be found some 4 degrees directly above faint Mars. The razor thin 27-day-old waning crescent Moon will cover or ‘occult’ Venus in our sky (event visible for much of western North America) on Wednesday morning, April 22: For southern Arizona this rare event should start around 5 a.m. MST. Observers using telescopes or giant binoculars to view should be set up and ready to go by 4:45 a.m. MST.
Mercury has perhaps its best apparition of the year this April. It starts very low, but bright, at -1.0 magnitude only 4 degrees above the western horizon 45 minutes after sunset on April 13 (though it will be visible a few days before this in brighter twilight). Each evening Mercury will then continue to lose brightness but gain altitude and move away from the glare of the Sun. On the evening of Saturday April 25 the razor thin Moon will lie will below much fainter Mercury (at magnitude 0.4) while on the following evening the Moon will lie above Mercury (and the Seven Sisters or Pleiades star cluster, above Mercury on that date). By then end of April into May you’ll need binoculars to spot now faint Mercury in a clear unobstructed horizon, before it moves into the glare of the Sun.
Mars is a difficult and faint object in the morning twilight. Starting April 9 it can be seen in binoculars (or perhaps with the unaided eye) some 12 degrees right (that’s southwest) of brilliant Venus. The two will be very low, only 4 degrees above the eastern horizon 50 minutes before sunrise. Because Mars is so faint right now and low in bright twilight, you may need binoculars to spot it in a clear unobstructed horizon. Faint Mars will be easier to find by the end of April when it moves higher in the twilight sky. Use the razor thin Moon to locate Mars on the morning of Wednesday morning, April 22, when Mars will lie some 4 degrees below or south of the Moon: On that morning, as mentioned above, this 27-day-old waning crescent Moon will cover or ‘occult’ Venus in our sky (event visible for much of western North America).
Bright Jupiter gains altitude each morning this April in the southeastern sky. By the end of April the giant planet is easily seen almost 25 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 is very close to and above (west of) Jupiter in our sky on the morning of Sunday April 19: Jupiter will lie only 1.25 degrees from the Moon’s edge as seen from the Desert Southwest that morning.
Visitors to Flandrau’s 16-inch 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 building is now closed on Thursday nights due to state budget cuts but the 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 towards the Pleiades, or ‘Seven Sisters’ star cluster.
APRIL EVENING STARS
  
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The bright stars of winter still dominate the evening April sky, but shift to the western half of the sky early. Look 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!
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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 first quarter Moon will occur on Thursday evening, April 2. The April Full Pink Moon rises on the evening of Thursday, April 9 and sets on the morning of Friday, April 10. The April last quarter Moon occurs on Friday morning April 17. The April 2009 new moon will occur on Friday, April 24.
Special Note: Starting in twilight on Wednesday morning, April 22 the razor thin 27-day-old waning crescent Moon will cover or ‘occult’ Venus in our sky (event visible for much of western North America): For southern Arizona this rare event should start around 5 a.m. MST; Observers using telescopes or giant binoculars to view should be set up and ready to go by 4:45 a.m. MST. This occultation is seen throughout North America, but is better seen in western states, especially the Desert Southwest, where both the disappearance and reappearance of the Moon are seen before sunrise. Use a wide-field telescope at low to moderate power to best view this rare event.
Also note: In the morning twilight of Monday, April 13, the 19 day old gibbous Moon will lie very close to (within 0.35 degrees) the bright reddish star Antares (the heart of Scorpius). The Moon is predicted to cover Antares from the westernmost portions of Mexico and possibly southern and southeastern parts of Arizona and New Mexico; However, this occultation is best seen from Hawaii.
Note: Additional information can be accessed by phone at Flandrau Science Center’s Astronomy Newsline at (520) 621-4310 or as a menu option at 621-S-T-A-R.
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