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28 Mar 2019

April Astronomy: This Month, the Morning Sky Offers a Preview of the Evening Sky This Summer

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My lifelong interest in sky-watching began in the school year 1951-52, a year after our sixth-grade teacher led us to create a mural of the solar system, with the planet sizes to scale.

When I was in seventh-grade, our school library included two books which really changed my life: A Dipper Full of Stars, by Lou Williams Page, originally published by in 1944—and revised and republished as a California state textbook in 1959! The other book was The Friendly Stars, by Martha Evans Martin, published in 1907.

On the first page of A Dipper Full of Stars is a quote from Harlan T. Stetson’s Man and the Stars: To acquire some appreciation of the meaning of the skies, one must make the friendship of the stars; watch their majestic march through the night, and the slow seasonal advance of constellation after constellation from east to west throughout the year. To know Orion, Sirius, Taurus, and the Pleiades as leading roles of the winter skies; or Lyra, with its Vega, Cygnus, with its Northern Cross, the Scorpion and Antares as the quieter leaders of the softer skies of summer, gives one a sense of kinship with nature which makes a knowledge of their movements more significant, and even life a bit more worthwhile.”

April is an interesting month to start keeping a record of bright stars seen each evening, within the first hour after sunset. Seven of the 16 stars of first-magnitude or brighter observable from the Coachella Valley are gathered in the western sky, arranged as the huge Winter Hexagon—clockwise starting with its brightest member, Sirius, Procyon, Pollux (with Castor nearby), Capella, Aldebaran, Rigel and back to Sirius to complete the Hexagon—with a bright red star, Betelgeuse, inside. Nearly all these stars will depart between late April and late June, as a result of the Earth’s revolution around the sun.

The morning sky features the planets Venus, Jupiter and Saturn. Mercury has a horizon-hugging apparition low in the morning twilight in April, lingering closely to the lower left of Venus at dawn in middle two weeks of month.

In the morning, the stars—but not the fast-moving planets Mercury and Venus—are in roughly the same positions they will occupy in the evening sky a few months hence: Bright steady Jupiter is in the south to south-southwest, with red twinkling Antares, heart of Scorpius, to its lower right, and steady Saturn to left of Jupiter. Golden Arcturus is in the west, with blue-white Spica to its lower left in the west-southwest. The Summer Triangle of Vega, Altair and Deneb passes overhead, as in evenings in August. Getting up before dawn is a good way to preview the sky of the coming season!

Events to observe:

April 1 at dawn: Venus is 8 degrees to the lower left of the waning crescent moon (13 percent). Binoculars may show Mercury rising in twilight, 10 degrees to the lower left of Venus.

April 1-6 at dusk: Mars and the Pleiades, or Seven Sisters, star cluster are 3 to 5 degrees apart, making a fine sight in the same field of view of binoculars. Mars’ trek across Taurus, at nearly two-thirds of a degree per day this month, will be fun to watch.

April 2 at dawn: Venus is within 5 degrees above the crescent moon (8 percent). Using binoculars, try for Mercury, 9 degrees to the lower left of Venus and 7 degrees left of the moon.

April 7-9: Enjoy a fine gathering of the moon, Mars, Aldebaran, Hyades and Pleiades at dusk.

April 10: Jupiter begins retrograde, and ends nearly 10 degrees farther west on the evening of Aug. 10. Saturn undergoes nearly 7 degrees of retrograde motion from April 30 through Sept. 19. It was a very close conjunction involving Saturn retrograding past the third-magnitude star Gamma in Virgo in the spring of 1952 which caught the attention of this writer, not quite 13 years old at the time.

April 10-23, dawn: Mercury stays no more than 5 degrees to the lower left of Venus, making it easy to locate through binoculars in this otherwise poor, low apparition. Mercury approaches within 4.3 degrees to the lower left of Venus April 15-18. Since these planets approach within 5 degrees but don’t pass each other, this event is known as a quasi-conjunction.

April 12: The moon is 7-12 degrees from Pollux and Castor, a pair of stars 4.5 degrees apart, marking the heads of Gemini, the Twins.

Night of April 13: Around this date each year, as the Earth passes between Spica and the sun, the star appears at opposition, nearly 180 degrees from the sun, and is visible all night. Look for Spica, the brightest star in Virgo, low in the east-southeast at dusk, and low in the west-southwest at dawn.

April 13-15: Mars passes 6.5 degrees north of Aldebaran at dusk. Binoculars give a fine view of the Hyades cluster in the same field as Aldebaran. Note two stars 8 degrees apart, marking tips of the Bull’s horns, 15-17 degrees above Aldebaran.

April 14: The moon is 4 degrees from Regulus, heart of Leo, the Lion.

Night of April 18-19: The full moon is 7-8 degrees from Spica all night.

April 22-26: The waning moon passes Antares, Jupiter and Saturn at dawn. The moon is 7 degrees above Antares on April 22, with close pairings of the moon and Jupiter on April 23 (less than one degree) and the moon and Saturn on April 25 (less than 2 degrees).

Check the website of the Astronomical Society of the Desert at www.astrorx.org for dates and times of our evening star parties at two locations:Sawmill Trailhead, our high-altitude site (elevation 4,000 feet), will next have sessions starting at dusk on Saturday, April 6 and May 4. Our primary, more accessible location is at the Visitor Center of the Santa Rosa and San Jacinto Mountains National Monument (on Highway 74, within 4 miles south of Highway 111 in Palm Desert). Our next session there is on Saturday, April 13, from 8 to 10 p.m., with the final one for the season on Saturday, May 11.

Also, remember to check the Impromptu Star Parties link. I’ll be offering sky watches in Palm Springs at the pedestrian bridge over Tahquitz Creek at North Riverside Drive and Camino Real, including some in predawn for the stars of summer, plus telescopic views of Jupiter and its moons, and Saturn’s rings; and some at dusk to observe the moon, Mars and the mix of winter and spring stars. Tentatively, I have predawn sky-watches scheduled each Sunday, and evening sky watches each Monday. Check the link for updates.

Wishing you clear skies!

Robert C. 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.

1 comment

  • Comment Link Virginie Gouband Tuesday, 02 April 2019 14:06 posted by Virginie Gouband

    Hello Robert Victor, thanks for your article.
    I am Virginie, a visual artist based in Paris working with light, and I was fascinated by the analemma you did in the 70' - 80'.
    I would like to share a picture of you on the facebook page of my non-profit organisation, named analemma, working on the organisation of exhibitions for young visual artists. Would you autorise me to use it?
    In case yes I will put the credit with your name.
    Thanks in advance for your response.
    Best,
    Virginie G

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