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30 Mar 2018

April Astronomy: The Month Brings a Meteor Shower, Brilliant Planets and a Constellation Framing the Moon

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The two brightest “stars” in the April evenings are really planets. Venus continues to gain altitude in the west to west-northwest at dusk, as the time of its setting shifts from 1.6 hours after sunset on April 1, to 2.2 hours after on the 30th. Jupiter doesn’t appear on our evening mid-twilight chart until almost month’s end; it rises in east-southeast just more than three hours after sunset on the 1st, to just more than a half-hour after on the 30th.

Next in brilliance at dusk are blue-white Sirius in the southwest; golden orange Arcturus climbing in the east-northeast to east; and yellow Capella, high in the northwest.

In the morning, Jupiter, in the southwest at dawn, is easily the brightest morning “star.” Ranking next are Arcturus in west, and Vega passing just a few degrees north of overhead. Mars, just east of due south, is slightly fainter than these stars as April begins. But as Earth closes its distance to Mars—from 103 million miles on the 1st to 79 million miles on the 30th—the planet begins to outshine those stars. In early April, Mars is closely accompanied by Saturn; they appear closest, within 1.3 degrees, on April 2. By month’s end, Mars-Saturn are 14 degrees apart.

Other bright stars in the morning sky are Altair and Deneb, completing the Summer Triangle with Vega; Antares, between Jupiter and Saturn, but below the line joining these two giant planets; and Spica, sinking in the west-southwest, to the lower right of Jupiter and lower left of Arcturus. On April 13, Spica is at opposition as the Earth passes between that star and the sun. On April 13-14, look for Spica in the east-southeast at dusk, well up in south in middle of night, and low in the west-southwest at dawn. Mercury, brightening slowly from magnitude +1.0 to +0.4 during April 19-30, is very low in the east in dawn twilight. In this poor apparition, binoculars are recommended.

On the morning of April 2, Spaceship Earth is heading toward a direction in space within 4 degrees east (to the left) of the Mars-Saturn pair. As our planet follows its nearly circular orbit around the sun, we will overtake all three bright outer planets, and each will take its turn at opposition and all-night visibility: Jupiter on May 8, (Antares on May 31), Saturn on June 27, and Mars on July 26. Mars, the next planet outward from Earth, will brighten spectacularly in July, outshining even Jupiter.

For events at dawn, the suggested viewing time is generally one hour before sunrise. For events at dusk, look one hour after sunset, except when noted.

Easter Sunday, April 1, at dawn: Spica is 6 degrees south of the moon in the west-southwest. Jupiter is in the south-southwest to southwest, 29 degrees to the upper left of the moon. The Mars-Saturn pair is in the south-southeast, 1.4 degrees apart, about 46 degrees left of Jupiter.

April 2 at dawn: Mars passes within 1.3 degrees south of (below) Saturn; the pair is 47 degrees east (left) of Jupiter. Red supergiant star Antares, heart of the Scorpion, is 19 degrees to the lower left of Jupiter and 29 degrees to the lower right of Mars.

April 3 at dawn: Mars-Saturn are 1.4 degrees apart. Jupiter is within 4 degrees to the lower left of the moon in the southwest. Four hours after sunset: The moon is low in the east-southeast, within 9 degrees to the lower left of Jupiter.

April 4 at dawn: Jupiter is 11 degrees to the lower right of the moon; Antares is 11 degrees to the lower left of the moon.

April 5 at dawn: Antares is within 10 degrees to the lower right of the moon. Mars-Saturn are 2 degrees apart.

April 6 at dawn: Mars-Saturn are 2.4 degrees apart, 12-14 degrees east (to the left) of the moon. Four solar system bodies—in order from west to east, Jupiter, the moon, Saturn and Mars—span 49 degrees.

April 7 at dawn: A beautiful gathering of the moon and two planets fits within the field of view of binoculars: Saturn about 1 degree to the moon’s lower right, with Mars just more than 3 degrees to the moon’s lower left.

Sunday, April 8 at dawn: The moon, in the south-southeast, has just passed last quarter phase and appears slightly less than half-full. All three bright morning planets are now west of the moon—Mars and Saturn by 9 and 12 degrees, respectively, and Jupiter by 59 degrees.

April 9 at dawn: Mars-Saturn are 4 degrees apart, 20 to 24 degrees to the upper right of the fat crescent moon.

April 11 at dawn: Mars-Saturn are 5 degrees apart.

April 12 at dawn: The distance from the crescent moon, low in the east-southeast, to Jupiter, in the southwest, spans 108 degrees. Dusk: Venus appears 15 degrees directly below the Pleiades star cluster, aka the Seven Sisters.

April 13 at dawn: This the last easy chance to view the waning crescent moon, rising within 10 degrees south of east in twilight; Spica is at opposition in the west-southwest. Between them, find Jupiter in the southwest, and Saturn and Mars 6 degrees apart in the south to south-southeast. At dusk: Find Spica low in the east-southeast. When Spica passes due south in the middle of night, look 36 degrees below it and only 3-4 degrees up for the globular cluster Omega Centauri, some 17,000 light-years away. Seen through binoculars in very dark skies, it appears as a round, fourth-magnitude fuzzy ball about as large as the moon.

Sunday, April 15: The new moon, closely south of the sun at 6:57 p.m., is invisible today!

April 16, about 25-40 minutes after sunset: From a place with an unobstructed view, some 10 degrees north of west, try to see the thin crescent moon, very low—2 to 5 degrees above the horizon—within 13 degrees below and slightly left of Venus. The moon’s age is about 25 hours past new. As the sky darkens, look for the Pleiades cluster 10 degrees above Venus. Binoculars give best views of the moon and of Pleiades.

From places with unobstructed views toward the east-southeast and west-northwest, Jupiter now rises just 8 minutes before Venus sets, and it is briefly possible to observe both planets simultaneously above opposite horizons. By April 24, Jupiter will rise one hour before Venus sets, so it will become easier to do so. By April 30, Jupiter will rise 99 minutes before Venus sets. It remains possible to observe these two bright planets simultaneously at dusk until early October, when Venus sinks into twilight.

April 17 at dawn: Mars and Saturn are 8 degrees apart. At dusk: Venus appears within 6 degrees to the right of the crescent moon, with earthshine illuminating the moon’s dark side.

April 18 at dusk: Don’t miss this special, beautiful sight! Within an hour after sunset, the moon is framed by the V-shaped head of Taurus, the Bull, composed of bright Aldebaran (marking the Bull’s eye 67 light years away, within 2 degrees to the moon’s upper left), and the fainter remaining stars of the “V,” members of the more distant Hyades cluster. Watch the moon close in on Aldebaran as the evening progresses. By 10 p.m., the star appears just 1 degree to the upper left of the moon’s center.

April 19 at dusk: Pleiades is 7 degrees to the upper right of Venus, with Aldebaran 13 degrees to the lower right of the moon.

April 20 at dusk: Betelgeuse, shoulder of Orion, is 15 degrees to the lower left of the moon. Below Betelgeuse, look for Orion’s three-star belt, and still lower, Orion’s foot, Rigel. Look for these stars each evening within an hour after sunset in coming weeks, and watch for their annual departures below the western horizon.

April 21 at dawn: Mars and Saturn are 10 degrees apart. Dusk: Pleiades is 5 degrees to the upper right of Venus. Pollux is 9 degrees to the upper right of the moon, with Procyon 15 degrees to the moon’s lower left.

Sunday, April 22, predawn darkness hours: It’s the peak of the Lyrid meteor shower. In early afternoon, the moon passes first quarter, 90 degrees east of the sun, and appears half full. In the late evening, the moon passes 2 degrees south of the Beehive cluster. You’ll need binoculars or a telescope to see the cluster’s stars so close to the moon.

April 23 at dusk: Regulus is 10 degrees to the lower left of the moon. Venus is within 4 degrees south (lower left) of Pleiades.

April 24 at dawn: Three bright outer planets—from west to east, Jupiter, Saturn and Mars—span 60 degrees. Mercury is also visible, very low in the east. Dusk: Regulus, heart of Leo, the Lion, is 4 degrees to the moon’s upper right. Venus’ least distance from Pleiades occurs tonight, as the planet passes 3.5 degrees south of the cluster’s brightest member.

April 25 at dusk: Pleiades is 4 degrees to the right of Venus, with Aldebaran 10 degrees to Venus’ upper left.

April 26 at dusk: Venus is nearly on line, joining Pleiades and Aldebaran.

April 27 at dusk: Spica is 11 degrees to the lower right of the moon.

April 28 at dusk: Spica is 8 degrees to the right of moon and a little higher. Watch for Jupiter rising 21 degrees to the lower left of the moon.

Sunday, April 29 at dusk: Venus is equidistant from Pleiades and Aldebaran—7 degrees from each. The full moon is 19 degrees to the lower left of Spica and 8 degrees above Jupiter.

April 30 at dawn: Jupiter is 5 degrees to the left of the moon in the southwest to west-southwest. Mars-Saturn are 14 degrees apart in the south-southeast to south. At dusk, watch for moonrise 6 degrees to the lower left of Jupiter in the east-southeast.

The website of the Astronomical Society of the Desert  has a listing of our evening star parties at two locations. The primary, more accessible location is at the visitor center of the Santa Rosa and San Jacinto Mountains National Monument (on Highway 74, within four miles south of Highway 111 in Palm Desert). A sky viewing session is scheduled there on Saturday, April 21, from 8 to 10 p.m. Sawmill Trailhead, our high-altitude site (elevation 4,000 feet), will have a star party starting at dusk on Saturday, April 14. Listings of star parties on the website include maps and directions for both locations. Star parties can be cancelled in poor observing weather. Also, check link to “Impromptu Star Parties” on that website for star parties announced on short notice.

Robert Victor was a staff astronomer at Abrams Planetarium at Michigan State University. He is now retired and enjoys providing sky watching opportunities for a variety of groups in the Coachella Valley. Robert D. Miller did graduate work in planetarium science and later astronomy and computer science at Michigan State University and remains active in research and public outreach in astronomy.

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