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02 Jun 2013

June Astronomy: This Month, Venus Is the 'Star'

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June Astronomy: This Month, Venus Is the 'Star' Robert D. Miller

During evening twilight in June 2013, the brilliant evening “star” Venus gleams very low in the west-northwest, while Mercury lingers nearby during the first three weeks.

Saturn glows yellowish and steadily, well up in the south-southeast to south, contrasting with the twinkling blue-white star Spica just 12 to 13 degrees to Saturn’s west (right).

On our evening all-sky chart, which you can see above, planets are plotted for each day when the sun has sunk to 9 degrees below the horizon, which we call “mid-twilight.” We have chosen that time, because we have found that by then, most planets and stars of first magnitude or brighter are easily visible to the unaided eye. In June, from Palm Springs, it takes 46 or 47 minutes after sunset to reach mid-twilight.

Planet positions are represented by a separate dot for each date, with the positions for each Saturday in June (1, 8, 15, 22, 29) represented by a larger dot and labeled. Using binoculars, folks with unobstructed views may spot Jupiter barely above the horizon on June 1 (look earlier to catch it higher). Rotate the chart until the portion of the horizon nearest to the cluster of planets low in the west-northwest is at the bottom of the circle, and you’ll see the cluster depicted at the same orientation as in the sky: Jupiter 4.5 degrees steeply lower right of bright Venus on June 1, and Mercury nearly as far to Venus’ upper left.

Note that Jupiter drops below the horizon in a couple of days, while Mercury and Venus climb a little higher each evening. Mercury reaches its peak altitude for this apparition around June 8, while Venus slows its climb and begins shifting to the left, or southward. In fact, on June 5, Venus sets the farthest north for this entire evening appearance, then starts a long southward trek until Nov. 6, when Venus will set far to the southwest.

In June, Mercury lingers 5 degrees above Venus for several days around June 6-7, and then starts to move closer to Venus. Pick out the planet dots for June 19; on that date, Mercury and Venus will appear closest, 1.9 degrees apart, with rapidly fading Mercury passing to the south (lower left) of Venus. Mercury dots are shown through June 27, but in practice, we’ll lose sight of it sooner: Mercury fades as it heads down toward the near side of the sun and becomes backlighted. Use binoculars to keep Mercury in view until the last possible date. By the last week in June, Venus will be the only planet remaining of the beautiful compact planet trio we enjoyed in late May.

One other planet resides in our June evening sky: Saturn tracks from south-southeast to south in mid-twilight as June progresses. The reason it drifts that way is that our Earth is moving in orbit around the sun, overtaking the outer planets. Stars on our chart drift westward for the same reason: The revolution of Earth around the sun. Notice the blue-white first-magnitude star Spica 12 to 13 degrees to the west (right) of Saturn and preceding it as both objects go westward across the sky. The stars’ daily positions aren’t plotted as individual dots, but are simply represented by tracks as the stars go west (counter-clockwise around the North Star) in the course of the month, or during a single night.

The brightest star in June’s evening sky is Arcturus, high above Saturn and Spica, and forming a large triangle with them. When the Big Dipper becomes visible, you can “follow the arc (of the handle) to Arcturus and drive a spike to Spica.”

Next after Arcturus in brilliance is Vega, climbing in the northeast. Compare the colors of these two stars! To Vega’s lower left is Deneb, and ascending into view later in the evening or later in the month is Altair, completing the “Summer Triangle.” Climbing in the southeast is reddish Antares, heart of the Scorpion.

In the west to northwest in early June is a curved arch of four stars topped by Pollux (and Castor, not shown, because at magnitude 1.6, it’s just a little fainter than the magnitude 1.5 brightness limit of our chart). These two stars make up the heads of Gemini, the Twins. To the Twins’ lower left is Procyon, the Little Dog Star, and in the northwest, anchoring the northern end of the arch, is Capella, the Mother Goat Star, ranking next after Vega in brightness.

Ranking last in brightness of the 16 stars of first magnitude or brighter visible in the course of a year from Southern California is 1.4-magnitude Regulus, heart of Leo, the Lion. Watch Regulus descend the western sky during June and July, before it passes on the far side of the Sun around August 23.

Follow the Moon

During June 10-23, the moon is above the horizon in evening mid-twilight. Follow it nightly as it waxes, or grows, from a thin crescent on June 10, through first guarter (half full) on June 16, to full on the night of June 22-23. The moon passes, in order, Venus and Mercury on June 10, the Twins on June 11, Regulus on June 13 and 14, Spica and Saturn during June 17-19, and Antares on June 21.

(The Abrams Planetarium monthly Sky Calendar illustrates such gatherings of moon, planets, and stars. To view a sample issue, visit www.pa.msu.edu/abrams/SkyCalendar.)

Full moon at 4:32 a.m. PDT on Sunday, June 23, nearly coincides with the moon’s closest approach of the year, 221,824 miles from Earth.

From the Coachella Valley on Saturday, June 22, the moon rises in the east-southeast at 7:22 p.m. PDT, about 38 minutes before sunset. On Sunday morning, June 23, the moon sets in the west-southwest at 5:55 a.m., 19 minutes after sunrise (after the moon has been up all night). And on that Sunday evening, the moon rises in the east-southeast at 8:21 p.m., some 21 minutes after sunset.

Does the full moon at rising or setting seem unusually large this month? Note that the moon at rising or setting always seems large (the “moon illusion”), even when it is at its most distant from Earth.

For those who enjoy watching or photographing the Moon’s big reddened disk coming up over distant mountains, here are moonrise times for the Coachella Valley for a few evenings after full. Times are when the foon’s disk would just start to appear over an ideal, flat horizon. In practice, our mountainous surroundings may delay risings and hasten settings by several minutes.

Monday, June 24: 9:13 p.m.

Tuesday, June 25: 9:59 p.m.

Wednesday, June 26: 10:40 p.m.

Thursday, June 27: 11:17 p.m.

Friday, June 28: 11:52 p.m.

Robert C. Victor was a staff astronomer at Abrams Planetarium at Michigan State University. He is now retired and enjoys providing skywatching opportunities for school children in and around Palm Springs. 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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