Stellar Vista Observatory Sky Report
John Mosley
July 4 – 10
The Sky Report is presented as a public service by the Stellar Vista Observatory, a nonprofit organization based in Kanab, Utah, which provides opportunities for people to observe, appreciate, and comprehend our starry night sky. Additional information is at www.stellarvistaobservatory.org. Send questions and comments to [email protected].
There’s nothing to see, but the Earth at aphelion – its farthest point from the sun – at 1:10 a.m. MDT on Monday, when the distance from the center of the earth to the center of the sun is 94,509,598 miles. This is 3.4% farther than when we are closest to the sun in January. It’s warm now in the northern hemisphere because our hemisphere is tilted toward the sun, which rides high in the sky, and because our days are long.
Seasons are reversed in the Southern Hemisphere because at the same time they are tilted away from the sun (we can’t both be tilted in the same direction!) and their days are short. There is no reason why aphelion has to occur in our summer and in fact it doesn’t always; it slips around the calendar in a roughly 23,000-year cycle (Google “earth apsidal precession”.)
This week the only real movement in the evening sky is the moon, which grows from a thick crescent to nearly full. Astronomers express the phase of the moon as its “age” which is the number of days since it was new. The moon was new at 8:52 p.m. MDT on June 28, and so at 9 p.m. on Monday its age is 5.4 days. On the 10th its age is 11.7 days. When full, at 12:38 p.m. on July 13, its age will be 14.7 days, which is one-half a lunar month as measured from new moon to new moon.
This week the moon passes from Leo through Virgo, then Libra, Scorpius, spending a few hours in Ophiuchus according to the way modern astronomers divide the sky The moon is in Ophiuchus, the Serpent Bearer or Healer, for only seven hours on the 10th, roughly from 3:30-10:30 p.m., when it has an age of 11.7 days.
That night the moon is a scant 2½ degrees, or five moon-diameters, from Antares, the brightest star in Scorpius and one of the brightest stars in the sky. You’ll see both together in any binoculars, and binoculars will help bring out the orange color of Antares. “Antares” means “rival of Mars” as it rivals Mars in the redness of its color.
The morning sky is littered with planets: Venus, Mars, Jupiter, and Saturn, strung in a line in that order from east to west. Venus is by far the brightest; rising a full two hours before the sun it is still quite low in morning twilight. Jupiter is not as bright but looks brighter because you see it against a darker sky. Jupiter is half-way up the southeastern sky in morning twilight.
Mars is 3 magnitudes fainter, or 1/15th as bright, but that’s still as bright as the brighter stars. Mars is 20-some degrees to the east of Jupiter. Saturn is the same brightness as Mars and it’s a full 40-plus degrees to the west of Jupiter. Remember that the width of your fist held at arm’s length is about 10 degrees.