A Predawn Lunar Eclipse, a Transit of Venus, and Other Sky Phenomena in June 2012 and Beyond

by Robert C. Victor

We hope you enjoyed the annular or partial solar eclipse of May 20. Perhaps you’ll want to start planning to take in the next two total solar eclipses within the U.S.: On August 21, 2017 (seen as total within a narrow path from Oregon to South Carolina), and on April 8, 2024 (total from Texas to Maine).

Here are some fascinating events to close out the (traditional schedule) school year, and some very striking arrangements of planets, moon and stars to encourage your students to “keep looking up” during the summer months.

June 2012 brings Californians a partial lunar eclipse in the predawn hours on Monday, June 4, and a rare transit of Venus across the face of the Sun on the afternoon of Tuesday, June 5, an event not to happen again for more than a century! Within a week later, and certainly by mid-June, Venus emerges into morning twilight to the lower left of Jupiter. Venus then displays a thin crescent phase, filling out to half full by mid-August while its disk size shrinks as the planet recedes from Earth. Venus will reach peak brilliance in predawn skies in mid-July. In late June and early July, Venus and Jupiter form a brilliant pairing before dawn, an encore of their evening pairing in March. Mars-Saturn remain in the evening sky, the gap between them closing until their trio with Spica in August.

Partial lunar eclipse in predawn on Monday, June 4: moon enters the umbra, or dark central core of Earth’s shadow, around 3:00 a.m. PDT; greatest eclipse (magnitude 37 percent, or 3/8 of the moon’s diameter in dark shadow) occurs at 4:03 a.m. PDT, with moon low in SW, above Antares, heart of the Scorpion. The moon leaves the umbra at 5:06 a.m. PDT. Of all the contiguous 48 states, California has the best view of this eclipse.

On Tuesday, June 5, the transit of Venus will be the last one until December 10, 2117. It begins in the afternoon, at 3:06 p.m. PDT along the U.S. West Coast. The event opens with a ~ 17.6-minute ingress until about 3:23 p.m., as Venus’ disk, 1/32 of the Sun’s apparent diameter, slides onto the solar limb. Venus takes about 6 hours to reach the opposite limb, so for most of North America the transit is still in progress at sunset. For details, including history, safe methods of observing, maps and timetables of visibility, visit: 

http://eclipse.gsfc.nasa.gov/OH/transit12.html

http://eclipse.gsfc.nasa.gov/SEhelp/safety.html

http://www.transitofvenus.org/

http://www.astroadventures.net/eyesafety.html

I plan to have students observe the start of the transit near the close of the school day at Cahuilla Elementary School in Palm Springs, and then visit other locations in the Coachella Valley until the Sun drops below the mountains. Peter A’Hearn, K-12 Science Specialist for Palm Springs Unified School District, plans to host a continuous transit watch in a park adjacent to Vista del Monte Elementary School. We will use solar filters suitable for safe viewing of solar eclipses with unaided eye, and telescopes fitted with front aperture filters for safely viewing the Sun in detail.

The Moon and Planets in June 2012

Morning planets: Jupiter rises in ENE in midtwilight (when Sun is 9° below the horizon) by June 5, and Venus by June 17. These two planets will form a spectacular pair within 5° in late June and early July. Follow Venus until sunrise and observe its crescent, one percent full on June 11, to 5 percent on June 18, and 16 percent on June 30. The planet’s disk, nearly one arcminute (1/60 of a degree) across during transit on June 5, is still 3/4 arcminute across on June 30, enough for 7-power binoculars to resolve the crescent in bright twilight or in daylight.

Mercury, passing superior conjunction May 27 and perihelion May 29, emerges quickly and brightly into WNW, setting after midtwilight by June 4. Binoculars help spot it in bright twilight first few days. Mercury shines at magnitude –1.5 on June 2, then fades, to –1.0 on June 7, –0.5 on June 14, 0.0 on June 22-23, +0.5 on July 1, and +1.0 on July 8.  Mercury passes Venus on June 1, Pollux on June 20, and closely aligns with the Gemini Twins Castor and Pollux on June 23 and 24.

Saturn, shining at mag. +0.5 to +0.7, drifts through S and SSW at dusk in course of June, staying within 5° of +1.0-mag. Spica. (Saturn ends retrograde June 25.) Through a telescope, rings reach a temporary minimum of 12.5° from edgewise, owing to motion of Earth around Sun. In the longer term, as Saturn orbits the Sun, the rings will “max out” at 27° from edgewise in 2017.

Mars in June fades from mag. +0.5 to +0.9 in SW to WSW at dusk, while shifting east 0.4° to 0.5° daily against stars of Leo-Virgo. On June 25-26, Mars is midway between Regulus and Saturn, 26°-27° from each. On Aug. 13-14, Mars will pass between Saturn and Spica, forming a striking compact, nearly straight-line trio in the WSW at dusk. In surrounding days, from August 7 to 20, the three objects will form a triangle no more than 5° on a side.

Moon near planets, June through August

Sun. June 17 at dawn: Waning crescent old moon low in ENE, between Jupiter to its upper right, and Venus rising to its lower left.

Thurs. June 21 at dusk: First easy waxing crescent young moon low in WNW. To moon’s upper right, locate Mercury, Pollux, and Castor.

Mon. & Tues. June 25 and 26 at nightfall: moon near Mars. Moon passes First Quarter phase (half full and 90° or one-quarter circle east of Sun) on June 26.

Wed. & Thurs. June 27 and 28 at nightfall: Waxing gibbous moon near Saturn and Spica. Saturn is the higher and brighter of the two “stars” near the moon.

Sun. July 15, about 1-1/2 hours before sunrise: Spectacular gathering of waning crescent moon, Venus, Jupiter, the star Aldebaran, and the Hyades star cluster, with the Pleiades or Seven Sisters star cluster not far above. Wonderful views for unaided eye and binoculars.

Mon.-Wed. July 23-25 at nightfall: Fat waxing crescent moon, approaching First Quarter phase, slips past Mars, Saturn, and Spica. On the middle date, Saturn-Spica are 4.5° apart, with Mars 12° to their west (lower right), forming a nearly isosceles triangle.

Sat. August 11, about 1-1/2 hours before sunrise: moon near Jupiter, Aldebaran, and the Hyades. The waning crescent moon will interfere little with the peak of the Perseid meteor shower in the predawn hours of Sunday.

Mon. August 13, about 1-1/2 hours before sunrise: moon near Venus. A perfect day for using the moon to follow Venus long into daylight hours! The moon will occult Venus between 1 p.m. and 2 p.m. PDT from West Coast. For a map and timetable of disappearance and reappearance of Venus, go to www.lunar-occultations.com/iota/planets/0813venus.htm.

Wed. August 15, about one hour before sunrise: Mercury very low in ENE, to lower left of old crescent moon. On Thursday, look about 45 minutes before sunrise to catch an even older crescent moon rising to lower right of Mercury.

Tues. August 21, one hour after sunset: Waxing crescent moon about 4-1/2 days after New, is low in WSW below a compact triangle of Saturn, Mars, and Spica. Four bodies within a 6.5° field! Can you fit all four within the field of view of 7-power binoculars?

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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Written by 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.