March/April 2017 – Vol. 29 No. 6

Celestial Highlights for April 2014

Posted: Tuesday, April 1st, 2014

by Robert Victor and  Robert D. Miller

Mars at its closest and brightest, a total lunar eclipse, two asteroids within easy reach of binoculars, and a whole slew of bright stars preparing for their annual departure from the western early evening sky.

April 2014 at dusk 

Southern California viewers, your evening twilight map is available here. Northern California viewers will find your map online.

Jupiter at mag. –2.2 to –2.0 is clearly the brightest evening “star”. Mars, varying from mag. –1.4 to –1.5 to –1.2 in April, briefly equals or slightly outshines Sirius (–1.4) as the red planet passes opposition and closest approach to Earth in the second week. Next in apparent brightness, in a virtual 3-way tie: Arcturus (–0.05) and Capella (+0.08), are high in the sky and well seen, but Vega (+0.03), just rising at month’s end from northern California, is much dimmed by our atmosphere, as is Saturn, also just rising around mid-twilight at month’s end

Going, going, … Jupiter, Betelgeuse, and the surrounding stars of the Winter Hexagon are in various stages of descent into the western sky. Beginning by mid-April, students can use the observing log  to keep daily records of their sightings of bright stars and planets during evening twilight, as well as any sounds of nature they hear during the observing sessions.

In the eastern half of the sky, Regulus, Arcturus, and (barely) Mars are already up and ascending on April 1. Mars is at opposition to the Sun and visible all night on April 8, followed by Spica just 5 days later.

The Moon forms striking gatherings with stars and planets during the first half of April. (If you spotted the 32-hour young crescent Moon low in the west at dusk on March 31, congratulations!) The waxing crescent with earthshine on its dark side will be a beautiful sight for the first several evenings of April as it climbs higher each night.

On Thursday evening, April 3, the Moon will appear closely lower right of Aldebaran, eye of Taurus, and among the stars along the right side of the “V” of the Hyades star cluster forming the Bull’s face. Sometime between 8:00 p.m. PDT (in NW corner of California) and 8:20 p.m. (in SE corner of our state), the leading dark edge of the Moon will occult, or cover the 4th-mag. star Delta-3 Tauri, causing the star to suddenly “wink” out. The occultation will be best seen in binoculars or a telescope. The event takes place in twilight, only 15 minutes after sunset in the NW corner of California and likely too difficult to observe, improving to near the end of twilight in the SE corner of the state. Sample times of the star’s disappearance: 8:06 p.m. in San Francisco and Sacramento, 8:15 p.m. in Los Angeles, and 8:17 p.m. in San Diego and Palm Springs. Just over an hour later (about 9:25 p.m. in Palm Springs), the star reappears, but at the bright edge of the Moon, where it will not be as easy to observe the exact moment of emersion.

On Sunday evening, Apr. 6, the Moon, nearing First Quarter phase (half full and 90° east of the Sun), passes 5° S of Jupiter. On the next evening, the Moon is widely S of Pollux, one of the Gemini Twins, and on Thurs. Apr. 10 it passes widely S of Regulus, heart of Leo, the Lion.

During all those evenings, the waxing Moon has been tracking south of the ecliptic, or “below” Earth’s orbital plane. But that will come to an end late on the night of April 14, as the Full Moon returns close enough to the ecliptic plane to be completely immersed in the umbra, or dark central core of Earth shadow – causing a total lunar eclipse!

The eclipse begins as the Moon begins to enter the Earth’s umbra, or dark central core of Earth’s shadow, late on Monday evening, April 14, at 10:58 p.m. PDT. Not long after the partial eclipse gets underway, the circular shape of the edge of Earth’s shadow will become evident.

The Earth’s diameter is nearly 3.7 times the Moon’s, but the Earth’s shadow, during this eclipse, will appear only 2.7 times as large as the lunar disk. That’s still large enough for the Moon to easily fit within it, with plenty of room to spare!

As more of the Moon is immersed in Earth’s shadow, the reddish color of the shadow becomes noticeable. The reddish illumination is sunlight which has passed through the Earth’s atmosphere and gotten refracted, or bent, into the Earth’s shadow. When light passes through Earth’s atmosphere, most of the bluer light (of shorter wavelengths) gets scattered by molecules in the air, and most of the red light gets through.

Total eclipse begins at 12:07 a.m. early Tuesday morning, April 15, as the Moon first becomes completely immersed in the umbra. Even so, the Moon may have a bright edge to it (the WSW limb, closest to Spica), because the shadow’s outer edge is usually much brighter than the center, which receives only sunlight which has passed deep within Earth’s atmosphere on its way to the Moon.

The brightness and color of the Moon during a total eclipse varies widely from one eclipse to another, depending on atmospheric conditions over places on Earth where Sun is rising or setting at time of eclipse. Sunlight must pass through these zones in order to reach Moon during total eclipse, and presence of clouds in lower atmosphere or volcanic aerosols in stratosphere can block much of the sunlight and darken Earth’s shadow. The great volcanic eruptions of 1963, 1982, and 1991 were each followed by exceptionally dark total lunar eclipses. The French astronomer Andre Danjon devised a five-point brightness or luminosity scale to help observers rate darkness and color of a total lunar eclipse. Observe for yourself how the eclipse on night of April 14-15 compares to others! Get Danjon’s scale  and then select the rating from the 5-point L (luminosity) scale best matching the darkness and color of the Moon at beginning, middle, and end of totality.

The 78 minutes of total eclipse is also a perfect time for using binoculars to locate the asteroids Vesta (mag. 5.7) and Ceres (mag. 7.0), at peak brightness and just 2.4° apart in Virgo, an easy star-hop from the dimmed Moon and Spica. These asteroids are the destinations of the Dawn space mission; Dawn has already visited Vesta and is on its way to Ceres, arriving there in 2015. See the very simplified Ceres-Vesta finder chart in this article for use just during the eclipse.

Deepest eclipse occurs at 12:46 a.m. PDT, when the northern edge of the Moon comes closest to the center of Earth’s shadow.

Total eclipse ends at 1:25 a.m., when the Moon’s SE limb begins to come out of Earth’s shadow.

The Moon’s withdrawal from the umbra is complete, and the concluding partial eclipse is over, at 2:33 a.m. PDT.

For perhaps half an hour before 10:58 p.m. and after 2:33 a.m., a light dusky shading – the penumbra, or region of partial shadow – may be noticed on a portion of the Moon’s disk.

April 2014 at dawn

Southern California viewers, your morning twilight map is available here. Northern California viewers will find your map online

Venus (mag. –4.4 to –4.1) continues to dominate the morning sky. Find it in the ESE in morning mid-twilight, drifting farther north as month progresses. A telescope shows Venus in gibbous phase, fattening from 54 to 66 percent full, while the disk shrinks from 22 to 17 arcseconds across. Saturn is a steady yellow “star” of mag. +0.3 to +0.1 sinking slowly in SW. Telescopes reveal the rings tipped 22° from edgewise. To Saturn’s lower right are bright reddish Mars and blue-white first-magnitude Spica, but they drop below the W to WSW horizon before month’s end, after passing opposition on April 8 and 13, respectively.

Other bright objects in the morning sky are golden Arcturus, well up in W to upper right of Mars and Spica; reddish Antares, heart of Scorpius, in SSW to SW; and the Summer Triangle of Vega, Altair, and Deneb high in the east, topped by its brightest member, Vega, approaching overhead.

April’s waning Moon, just hours after the lunar eclipse, is still close to Spica and Mars at dawn on the 15th. Early on the morning of the 17th, the Moon passes closely south of Saturn, and on the next morning, Apr. 18, the gibbous Moon passes widely north of Antares. The Last Quarter (half full) Moon on the morning of Apr. 22 will be 5° north of the ecliptic, near stars marking the head of Capricornus, the Sea-goat. On the mornings of April 25 and 26, the crescent Moon will appear near Venus. One week after Last Quarter, at the New Moon of Apr. 29, our satellite will pass through the descending node of its orbit and cause a solar eclipse, annular in a small part of Antarctica, and partial in Australia and the south Indian Ocean.

Moon returns to evening sky. At dusk on April 30, the young 1.9-day-old crescent Moon appears low in WNW to the lower right of Aldebaran. In the 27 days since April 3, the Moon has completed nearly one circuit around the zodiac, and a very eventful trip at that! (The Moon’s sidereal, or star-to-same-star, period is 27.3 days.)

Future events: In May, four bright planets adorn the sky at dusk, and Venus will have a very close conjunction with the Moon at dawn, the best one during Venus’ current morning apparition. There’s a good chance for a really strong but brief meteor outburst (a storm?) on the night of May 23-24. All these events will be illustrated or described in the May 2014 issue of the Abrams Planetarium Sky Calendar,

This month’s lunar eclipse is the first of a tetrad, four consecutive total lunar eclipses at six-month intervals. And all are visible from California! For this one, the 78-minute totality began at 12:07 a.m. on Tues. April 15. The next will occur on Wed. Oct. 8, with a 59-minute totality getting underway at 3:25 a.m.

Then in 2015, on Sat. April 4, a very brief 5-minute totality will commence at 4:58 a.m.  And, finally, later that year, on Sunday, Sept. 27, a 72-minute totality will get underway at the very family-friendly time of 7:11 p.m.

This year’s opposition of Mars on April 8, with close approach 57 million miles from Earth on April 14, will be improved upon in coming years. In late May 2016 Mars will approach within 47 million miles of Earth, and in late July 2018, it will come even closer, within 36 million miles. But at both those apparitions Mars will appear much lower in the sky where seeing is usually poor, so take advantage of this spring’s opportunity for close-up views of Mars through a telescope. For helpful tips, click here.

Robert D. Miller, who provided the twilight charts, 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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Written by Robert Victor

Robert Victor

Robert C. Victor was Staff Astronomer at Abrams Planetarium, Michigan State University. He is now retired and enjoys providing skywatching opportunities for school children in and around Palm Springs, CA. Robert is a member of CSTA.

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