In the Sky This Month

Eltanin, an Arabic name that means “the serpent,” is the brightest star of Draco, the dragon, which is high in the north on summer evenings. Eltanin is as bright as the nearby North Star, Polaris.

Ophiuchus, the serpent bearer, passes high across the south tonight, above Sagittarius and Scorpius. Ophiuchus is the only one of the 13 constellations along the Sun’s path that is not a member of the zodiac.

Summer begins tonight in the northern hemisphere, when the Sun stands farthest north for the year — a moment known as the summer solstice. The season lasts until the September equinox, when the Sun crosses the equator from north to south.

Venus, the brilliant “morning star,” will stand to the left of the Moon at first light tomorrow, and about the same distance to the upper right of the Moon on Wednesday.

Summer arrives on Tuesday night, with the summer solstice. Tuesday and Wednesday will be the longest days of the year here in the United States — the greatest intervals between sunrise and sunset.

The timekeeper for the United States, the Naval Observatory, defines sunrise and sunset as the moments when the center of the Sun is physically 50 minutes of arc below the horizon, which is less than the width of your finger held at arm’s length.

Hydra, the water snake, slithers quite low across the southwest at nightfall. One of its treasures is the binary system V Hydra. Its main star is old and puffed up. It expels gas into space, which the second star grabs, then shoots out like cannonballs.

The last gasp of a dying star climbs the eastern sky on June evenings. The Ring Nebula is not far to the lower right of the brightt star Vega, which is about halfway up the sky as night falls. The nebula consists of the ejected outer layers of a once-normal star.

Hercules and Ophiuchus are in the east this evening. Hercules is named for the Greek hero, while Ophiuchus, the serpent-bearer, is named for the mythological founder of Greek medicine. Both joined Jason aboard the Argo in search of the golden fleece.

Altair, one of the closest and brightest stars in the night sky, is in good view on June evenings. It forms the southern point of the Summer Triangle, which is low in the east and northeast at nightfall, and wheels high across the sky during the night.