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June Skies: Short Nights, Much to See

by Howard L. Cohen

Summer "officially" arrives for the Earth's Northern Hemisphere on June 21 at 4:34 p.m. EDT. During summer, Floridians have more hours of sunshine but less star light. In Gainesville, old Sol hides for only 9h56m on Solstice Day. Eliminate twilight and dark sky time is brief during summer months.

Summer thunderstorms can also dampen observing time, humidity is typically high, and mosquitoes go on a feeding binge. Armchair astronomy is a solution but June skies should tempt you outside. Here is a summary of a few sky events—see your favorite astronomy magazine for more info. Begin by looking for dazzling golden Arcturus (mag. -0.04) high over the southern horizon. (Follow the Dipper's handle to Arcturus.) Did you know that only Sirius shines brighter for most of the USA? The Big Dipper, itself, is an easy object in June because it "rides high" over the northern horizon during evening hours. Observers with telescopes should search Ursa Major and nearby regions for fine collections of galaxies. Examples: M51 ("Whirlpool"), M94 ("Multi-arm"), M81/82 ("Exploding"), M101("Pinwheel"). And don't forget M104 ("Sombrero") in Virgo.

Low in the northeast, watch the Summer Triangle" rise (three first magnitude stars, Vega, Deneb and Altair, in the constellations of Lyra, Cygnus and Aquila respectively). Lyra is famous for a planetary nebula, the "Ring" (M57)—it looks like a "smoke ring" in a telescope—and a double, double star (Epsilon Lyrae), a fourth magnitude, naked eye pair, each double with companions only 2–3 arc seconds away. And don't miss Albireo (Beta Cygni) in the head of Cygnus (the Swan). A small telescope reveals that this golden yellow star (mag. +3.1) has a fainter, bluish companion (mag. +5.1) only 35 arc seconds away. The color contrast is dramatic! (Both Epsilon Lyrae and Beta Cygni are examples of visual binaries.)

Also try finding the "Great Globular Cluster" in Hercules (M13), located one-third of the way from Eta Herculis to Zeta Herculis, two stars that form the west side of the "Keystone". M13 is a naked eye object if skies are dark and you have good eyesight. (It looks like a small, fuzzy patch in binoculars.) Moderate size telescopes resolve thousands of stars in this huge cluster 21,000 light years away!

This June is an excellent time to watch the wandering motion of planets. First, Mars and Regulus in Leo make a striking pair. On June 1, Mars, redder and slightly brighter (mag. +0.9), is 4 degrees northeast of whitish Regulus (mag. +1.4). By month's end, Mars will drift 15 degrees farther east and have become nearly identical in magnitude to Regulus! Second, Jupiter and orange tinged Antares also make an interesting combo. At the beginning of the month, both objects rise simultaneously at sunset in the southeast and are well placed for observation by 10:00 p.m. EDT. Jupiter, dazzling summer skies at magnitude -2.6, will spin westward from 5 degrees northeast to nearly 6 degrees north of Antares by month's end. Jupiter's motion westward relative to Antares, is a celestial movement called retrograde motion. (Note that Mars moves eastward relative to the stars during June, a motion called direct or prograde.)

Early morning observers should hunt for Mercury, which reaches greatest western elongation from the Sun (22°) June 22. Mercury is difficult to find because it always appears near the Sun. Greatest elongations often provide good opportunities to see this elusive planet. Unfortunately Mercury will lie south of the ecliptic, reducing its altitude above the horizon. However, the ecliptic's steep angle to the horizon in June helps, especially for the South USA. Look for Mercury (mag. +0.5) ten degrees above the east northeast horizon one-half hour before sunrise (6:32 a.m. EDT). Do not confuse Mercury with bright Venus (mag. -3.9), several degrees to the east (left) only five degrees above the horizon.

Before hunting for Mercury, look for Saturn (mag. +1.3), now well above the southeast horizon at 5:30 a.m. Since the Earth recently passed through Saturn's ring plane (May 21), seeing rings is difficult (ring tilt 0.6°). However, use a telescope to look for the ring shadow, a black line across Saturn's equator!

Finally, advanced sky watchers with large telescopes should search for Pluto (mag. +13.7), well placed for observation in late evening. You will need very dark, clear skies to find dim Pluto. Easier are Uranus and Neptune (see finding charts in Sky and Telescope, April, pp. 70– 71). Note that star gazers can now see all nine planets during a single, June night!

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Notes:

ecliptic  apparent yearly path of Sun on sky.
elongation  angular separation on sky between two objects.
magnitude  brightness—smaller numbers signify brighter objects. (Naked eye limit is about mag. +6.)
Sirius  brightest nighttime star (magnitude is about -1.5)
visual binary  a star seen as a double star due to the close physical proximity of the two stars (each orbits the other).

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