Skywatching, March and April 2011

by Robert Victor

All-sky evening star charts and sky calendars for March and April 2011, illustrating events mentioned in this article, such as the moon passing planets and bright stars, and the Mercury-Jupiter pairing low in the west at dusk around March 15, can be found on the web at www.pa.msu.edu/abrams/ABDNHAMar-AprSkies/.

Follow the Moon!

The moon’s orbit stands nearly vertical in the sky soon after sunset each year in late winter/early spring for observers at mid-northern latitudes. In 2011, dates to follow the moon’s progress at dusk from thin crescent to Full are March 6-19 and April 4-17. On the first evening of each interval, the moon is not far above the horizon and the very thin crescent may be difficult to spot, especially if you have mountains to your west. Challenge your students to observe the young very thin crescent moon on Saturday, March 5, within 30 hours after new. About 25 minutes after sunset, the crescent sliver will be just 7 degrees up in the west and 13 degrees lower right of Jupiter. Notice its horns, pointing away from the sun, are pointing straight up!

For the next week, the moon climbs much higher each evening as it passes the bright stars of the zodiac. Encourage your students to face west about half an hour after sunset on Sunday March 6. Those who do so will be rewarded by the sight of a beautiful crescent moon not far to the right of Jupiter. On that date and on the next few evenings, as the sky darkens, alert your students to look for the faint bluish glow of earthshine on the moon’s dark, non-sunlit side.

By the latter half of the week of March 6-12, students may also begin to notice the planet Mercury a few degrees to the lower right of bright Jupiter. On each successive evening, Jupiter appears lower, owing to Earth’s faster revolution around the sun, and Mercury appears higher, owing to the innermost planet’s even faster revolution, until on March 15, the two planets appear to pass each other. That evening, some 45 minutes after sunset, Mercury and Jupiter are just two degrees apart, with fainter Mercury to the right of Jupiter. This will be the best conjunction, or pairing, of bright planets in the evening sky this year!

As the waxing moon makes its way against the background of Taurus the Bull during March 10-12, it appears first near the Pleiades star cluster, and next evening near Aldebaran and the Hyades cluster,and finally near the Bull’s horns. (The star clusters, as well as the moon itself, will be wonderful targets to examine through binoculars!) On Saturday, March 12 the first quarter moon, half full and 90 degrees (a quarter-circle) from the sun, is just south of overhead at sunset. On March 15 the moon appears near Pollux and Castor, two bright stars marking the heads of Gemini, the Twins. On March 17, look for Regulus, heart of Leo, the Lion, to the upper left of the moon. The full moon of Saturday, March 19, rising soon after sunset and coinciding with perigee, buries itself far below the eastern horizon on subsequent nights. The result is an unusually long wait, about 1-1/4 hours from one day to next, to observe moonrise over next few nights.

If you wait until 2-1/2 hours after sunset on Saturday, March 19, you’ll find Saturn to the full moon’s lower left, and Spica below Saturn. At the same time on Sunday the 20th, the waning gibbous moon will appear closely to the upper right of Spica.

Attend an Evening Sky Watch, or Organize Your Own!

Many astronomy clubs, planetariums, and observatories often schedule public skywatching sessions on weekends close to the date of a first quarter moon. If there isn’t one in your area, organize your own! In March and April 2011, the best dates to hold school or public sky viewing sessions might be during March 9-15 and April 7-14. With the moon within three days of its first quarter (half full) phase of March 12 and April 10-11, our satellite will be ideal for observation with telescopes and binoculars, and not too bright to interfere with many favorite deep-sky objects. Begin shortly after sunset, viewing the waxing moon. In a session within 3-4 days of first quarter, lunar craters and other features near the moon’s terminator (the day-night boundary, where the sun is rising) will offer striking views through binoculars and telescopes. Californians may be reminded of the softer but still spectacular display of light and shadow in their surrounding mountains twice each day, at sunrise and at sunset.

During the recommended March dates, you may also see bright Jupiter low in the west, and possibly catch a glimpse of Mercury to its lower right, or just 2 degrees to Jupiter’s right on March 15. During the April dates, the ringed planet Saturn will ascend into fine view in the east-southeast by nightfall.

Although the Mercury-Jupiter pairing on March 15 will be very low in the west in twilight, it will be the brightest evening planetary conjunction of this year. (The year 2012 will offer much more, including a spectacular Venus-Jupiter pairing well up in the west on March 13, a deep solar eclipse on May 20, and a rare transit of Venus across the face of the Sun on June 5!)

Stars, Winter into Spring

At dusk in early March, Orion the Hunter is high in the southern sky, and eight of the 16 brightest stars (of first magnitude or brighter) ever visible from California are in view. Observers in southern counties can add seldom-noticed Canopus, reaching its high point just 4 degrees up due south from Borrego Springs at the end of twilight on March 7. This star transits (reaches its high point due south) about four minutes earlier each day, so watch for it on clear evenings in February and early March from places where mountains to the south don’t block your view.

Orion’s belt points the way to Sirius, brightest of all nighttime stars, reaching its high point 40 degrees up in south, just 21 minutes after Canopus transits.

We’ll see “the great Overdog” (described in Robert Frost’s poem “Canis Major”), “That heavenly beast/With a star in one eye [Sirius]/Gives a leap in the east./He dances upright/All the way to the west/And never drops/On his forefeet to rest./I am a poor underdog,/But to-night I will bark/With the great Overdog/That romps through the dark.”

After nightfall, use binoculars and telescopes to examine the best of the “Messier objects”, including star clusters, nebulae, and even a few galaxies outside the Milky Way. French astronomer Charles Messier in the late 1700’s, while searching for comets, often found objects which appeared similar to comets but weren’t, so he made a list of these “nuisance objects” that got in his way. This list, the Messier Catalog, contains many objects now regarded as favorite showpieces by amateur astronomers at star parties.

The Astronomical League, an organization for amateur astronomers (website www.astroleague.org), awards certificates to members who observe and record all the Messier objects. There’s even a certificate for the Binocular Messier Club, earned by observing just 50 of the 110 objects in Messier’s catalog. Combining evening and predawn sessions, or waiting until the current predawn constellations show up in the evening, your students can find several of the easiest Messier objects, and perhaps begin their quests to accomplish the requirements of the Binocular Messier certificate. There’s also a “Sky Puppy” certificate with emphasis on constellation study, for those who complete its requirements by their 11th birthday.

Within a few hours after sunset in early March, the Big Dipper’s handle will lead you to Arcturus rising in the east-northeast (a sure sign of spring), and Saturn and Spica rising south of east.  The hazy Beehive cluster passes just south of overhead, while all of winter’s prominent constellations, including Orion and his Dogs, the Bull, the Twins, and the Charioteer, adorn the western half of the sky. These six constellations include the huge “Winter Ellipse” incorporating seven stars of first magnitude or brighter, counting Orion’s shoulder Betelgeuse inside the giant oval. In the eastern half of the sky are three more stars, Regulus in Leo, Arcturus in the Herdsman or Bear-driver, and Spica in Virgo with the planet Saturn nearby. (See the star maps for lists of the brightest stars.)

Students should have access to a flashlight fitted with a red filter (a red LED flashlight is even better), warm clothing for comfort, and, if possible, binoculars for exploring the sky.  Feel free to reprint the star maps and Sky Calendars to help you find your way around the sky. Bring telescopes for viewing favorite astronomical objects.

Predawn Sky Watch

By viewing the sky before first light of dawn in early March, students can get a preview of the evening sky of late June/early July. You’ll find Leo the Lion setting in the west, and the Big Dipper in the northwest, with handle curving toward Arcturus and farther to Spica and nearby Saturn in the southwestern sky. The Summer Triangle of Vega-Altair-Deneb is high in the eastern sky, while reddish Antares, the heart of the Scorpion, is some 20 to 30 degrees up in the south, depending on your latitude. If you begin two hours before sunrise, you’d have at least half an hour to explore the spectacular star clouds of the Milky Way, appearing as “steam” rising from the spout of the Teapot of Sagittarius, and passing through the Summer Triangle. You can also view Saturn with rings tipped more than 9 degrees from edgewise. Before dawn in March, there are several fine Messier objects along the Milky Way to examine with binoculars and telescopes. First hint of dawn’s light should occur shortly after the start of astronomical twilight, when the sun is 18 degrees below the horizon, about 1-1/2 hours before sunrise. As the sky brightens, shift your telescopic viewing to double stars, and to Venus in gibbous phase in March 2011, low in east-southeast.

Specialties for Southern California

The low latitude of southern California provides residents and visitors opportunities to observe far southern objects. Here are two:

Canopus is the second-brightest star in the heavens, ranking after only Sirius, the Dog Star. At its best from Borrego Springs, Canopus appears just 4 degrees above the horizon, which happens when the star passes due south. That occurs at the start of morning twilight in mid-October each year, backing 4 minutes earlier each day or one hour per 15 days. Select a place where mountains to your south aren’t high enough to block your view. By November 23 the star passes due south around 2:00 a.m. PST, by December 23-24 near 12 midnight, by January 22 around 10:00 p.m., and by February 22 around 8:00 p.m. Around March 7 each year from southern California, Canopus is south around the end of evening twilight.

The Omega Centauri Globular Cluster, a globe of stars some 17,000 light years away, is now considered by astronomers to be the core of a dwarf spheroidal galaxy interacting with the Milky Way. It appears as a 4th-magnitude fuzzy spot about the apparent size of the moon, visible with unaided eye and easily visible in binoculars and telescopes. From Borrego Springs, it passes 9 degrees up when due south. This happens annually around January 18 at the start of astronomical morning twilight, then two hours earlier each month. On March 10 it passes due south around 2:00 a.m. PST, and (because of the change to daylight savings time) around 2:00 a.m. PDT on March 26. By April 24-25 it passes due south near midnight PDT, and by May 25 around 10:oo p.m. PDT. The season of best observing ends annually around June 1, when the cluster is due south at the end of evening twilight.

From Dark Sites –

The Zodiacal Light, mostly sunlight-illuminated comet dust in the inner solar system, can be seen best from very dark sites (California deserts fit the bill) right at the end of astronomical twilight on dates when the moon is absent or very thin. In March and April 2011, the best evenings are March 1-6, and March 21 – April 4. Look for a huge, softly luminous cone of light in the western sky, with its axis near the ecliptic (centerline of the zodiac where the Moon and planets are found), and its brightness greatest not far above the horizon and tapering off with increasing altitude and with increasing distance from the axis.

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.

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