The Night Sky of June

Dr. Wayne Wooten
Professor of Astronomy

The BIG EVENT for June 2012 is the transit of Venus in front of the sun on the afternoon of Tuesday, June 5th. This rare event will not occur again in our lifetimes; it will be 127 years before the alignments of Earth and Venus again cause Venus to appear to move across the visible disk of the sun.

For June 2012, the Moon will be full, the Honey Moon, on June 4th, so the two weeks finds the moon waning in the morning sky. On the 11th, the last quarter moon passes is high overhead at dawn in the morning sky. The waning crescent moon passes 1.4 degrees north of Jupiter in the morning sky on June 17th, and 2 degrees north of Venus on the 18th; note how fast Venus has moved from evening to morning sky!. New moon occurs on June 19th. The beginning of summer occurs at 6:07 PM CDT on June 20th, the longest day of the year, with about 14 hours of daylight for the Gulf Coast. The waxing crescent moon passes five degrees south of Mars on June 26th, and 6 degrees south of Saturn on June 28, one day after the first quarter moon.

High up in the southern sky is the most beautiful planet, Saturn, just northeast of Spica, the brightest star in Virgo. Saturn’s rings are now open about 12 degrees; they will continue opening up wider until 2017, when they are tilted 27 degrees toward us and the Sun. You may also see some belts and zones on the planet’s disk. The largest, Titan, will be seen in any small telescope, but others will need larger scopes to spot.

The winter constellations are being swallowed up in the Sun’s glare, but you might spot Sirius low in the SW as June begins. Sirius vanishes into the Sun’s glare by mid-June, and this sets the period as “Dog Days”, when Sirius lies lost in the Sun’s glare. In reality, Sirius is about 20x more luminous than our star, but also lies eight light years distant, while our star is eight light minutes away from us.

The brightest star in the NW is Capella, distinctively yellow in color. It is a giant star, almost exactly the same temperature as our Sun, but about 100X more luminous. Just south of it are the stellar twins, the Gemini, with Castor closer to Capella, and Pollux closer to the Little Dog Star, Procyon. By the end of June, all the winter stars, like Sirius, are vanished behind the Sun.

Overhead, the Big Dipper rides high. Good scouts know to take its leading pointers north to Polaris, the famed Pole Star. For us, it sits 30 degrees (our latitude) high in the north, while the rotating earth beneath makes all the other celestial bodies spin around it from east to west.

If you drop south from the bowl of the Big Dipper, Leo the Lion rides high. Note the Egyptian Sphinx is based on the shape of this Lion in the sky. Taking the arc in the Dipper’s handle, we “arc” SE to bright orange Arcturus, the brightest star of Spring. Cooler than our yellow Sun, and much poorer in heavy elements, some believe its strange motion reveals it to be an invading star from another smaller galaxy, now colliding with the Milky Way in Sagittarius in the summer sky. Moving almost perpendicular to the plane of our Milky Way, Arcturus was the first star in the sky where its proper motion across the historic sky was noted, by Edmund Halley.

Spike south to Spica, the hot blue star in Virgo, then curve to Corvus the Crow, a four sided grouping. It is above Corvus, in the arms of Virgo, where our large scopes will show members of the Virgo Supercluster, a swarm of over a thousand galaxies about 50 million light years away from us. Much closer, in the back yard of our own Milky Way, is the closest globular cluster, Omega Centauri. It is faintly visible to the naked eye directly below Corvus, and is a telescopic treat at our June gazes about ten degrees up over the Gulf. This huge cluster is now suspected of being the surviving remnant of a dwarf galaxy, like our deep southern companions, the Large and Small Magellanic Clouds, but with most of its gas and dust long ago stripped away by repeated passes through the disk of our own Galaxy.

To the east, Hercules is rising, with the nice globular cluster M-13 marked on your sky map and visible in binocs. While not as close as Omega Centauri, it is much higher in the sky, and also one of the top telescopic sights in good sized scopes. Several other good globular clusters are also shown and listed on the best binoc objects on the map back page.

The brightest star of the northern hemisphere, Vega (from Carl Sagan’s novel and movie, “Contact”), rises in the NE as twilight deepens. Twice as hot as our Sun, it appears blue-white, like most bright stars. Its constellation, tiny Lyra, looks like a parallogram just south of Vega, but was the harp of Orpheus in Greek legends.

In the southeast, Antares rises about the same time as Vega does, in the brightest of all constellations, Scorpius. Antares appears reddish (its Greek name means rival of Ares or Mars to the Latins) because it is half as hot as our yellow Sun; it is bright because it is a bloated red supergiant, big enough to swallow up our solar system all the way out to Saturn’s orbit!

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