April 2008
Skywatchers’ Guide for April 2008
PLANETS
April 2008 is a still a very good time to see Saturn and its ring system as Saturn and Earth are not far from their closest back in late February, and Saturn will be up nearly all night long. Saturn fades slightly to a less than 0.5 magnitude star-like object in April. Saturn climbs higher each night in the constellation Leo the Lion and is high overhead in the convenient evening hours (well placed for telescopic viewing). 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 drifts nearer (from three to two degrees) to Leo’s brightest star Regulus this month. The ringed planet is dimmer this year compared to previous years because its rings are more edge-on. Also, the waxing gibbous Moon is near and above Regulus (and Saturn) in our sky on Monday April 14 and below (closer to) Saturn on Tuesday evening, April 15. For more information on viewing Saturn in Flandrau’s 16-inch telescope and for special viewing of Saturn on Astronomy Day (May 10) click here.
Mars is conveniently high overhead in evening twilight, and is well placed for typical sharp telescopic viewing (the higher the altitude, the less air is being looked through). However Mars continues to shrink in apparent size (from 7 to 6 arc seconds in April) as Earth recedes from Mars in space, making it too small for viewing of surface contrast features, even in large, high quality telescopes at high power. Mars is currently visible starting 30 minutes after sunset when it is overhead in our northern hemisphere sky. During the month Mars fades from a fairly bright magnitude +0.6 (or as bright as Saturn) to a less bright 1st magnitude. Mars continues its eastward movement, creeping through the constellation of Gemini, the Twins. Mars is nearest (less than five degrees) to equally bright Pollux (Gemini’s brightest star) on April 26-28. Look for the thick waxing crescent Moon (one day before first quarter) near Mars in our sky on Friday evening of April 11. The Mars Phoenix Mission, led by the University of Arizona, is en route to Mars with arrival on the north pole of Mars on Memorial Day weekend, 2008. For information on this first University led mission to another planet, click here.
Mercury has its best evening apparition this year during the last half of April into early May (from April 16 through May 7). Observers in most of the continental United States (including mid-northern latitudes) will have to wait until the end of April (by April 26 for the Desert Southwest) for bright Mercury to climb as high as 5 degrees above the western horizon, starting 30 minutes after sunset. Mercury will be brightest late in April (at around magnitude -1) but fades each evening as it climbs in the evening sky into June. The first spacecraft to orbit Mercury, the MESSENGER spacecraft, arrived early this year in its first flyby of Mercury. For a link to see the latest images, and find details about the MESSENGER spacecraft and the Mission Operations Center, click here.
Bright Jupiter gains altitude each morning this April in the southeastern pre-dawn sky. By middle and late April the giant planet is easily seen over 30 degrees above the southern horizon (almost due south) one hour before sunrise (from the southern United States). Jupiter is east of the Teapot of Sagittarius and is the brightest star like object that is well up in the morning sky (much brighter Venus is only visible early in the month and then is very low and difficult to see). The waning gibbous Moon slides well below Jupiter in our sky on the morning of April 27.
In the first few days of April 2008 the brilliant planet Venus is sinking into the glare of the Sun and is very low and difficult in the bright morning twilight sky, 20 minutes before sunrise. At the start of April look for Venus in binoculars, only a few degrees above the east-southeast horizon starting 25-30 minutes before sunrise. Brilliant Venus can be seen in a clear sky (with an unobstructed eastern horizon). Venus is afterwards lost in the glare of the Sun until it reappears at the end of August.
Visitors to Flandrau’s 16-inch telescope should note that Mars and Saturn are both visible in the telescope during public hours. Flandrau’s 16-inch telescope is open for viewing during public hours, weather permitting, Wednesday through Saturday nights (excluding select holidays), from 7-10 p.m. 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 this month, note that it may appear to twinkle somewhat; however, 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
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!
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 washed out by moonlight
The relatively minor shower Lyrid shower peaks this year during the hours before dawn on April 21-22 but the nearly full moon washes out the sky, eliminating many of these fast meteors from view.
MOON PHASES
The new moon in April occurs on Sunday April 6. The April first quarter Moon will occur on Saturday evening, April 12. The April Full Pink Moon (as named by native Americans) rises on the evening of Saturday, April 19 and sets on the morning of Sunday, April 20. The April 2008 last quarter Moon will occur on Monday morning, April 28.
Special Note: Starting in twilight on Tuesday evening April 8th the waxing crescent Moon (3 days old) passes so close in our sky to the Pleiades, or Seven Sisters Star Cluster, that it will cover a few of the fainter stars in and around this bright cluster for the Desert Southwest. This occultation is seen throughout North America, but is best seen from around Illinois east into the northeastern USA and Canada where brighter stars are covered; Use a wide-field telescope at low to moderate power to best view this rare event.
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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