Observatory telescopes

In July the moon runs through an entire lunar cycle, from the new moon on the 2nd to the new moon on the 31st.

At the midpoint of every cycle we get a full moon, and July’s falls on the afternoon of the 16th. That evening we’re treated to the rising of a very round and lovely moon against a pale sky.

On the 9th, Earth laps Saturn in the orbital race. At this moment, called opposition, the ringed planet appears opposite the sun in the sky.

When an outer planet is near opposition, it rises in the east around sunset and is up all night. This summer Saturn travels the night sky east of the Teapot of Sagittarius and right below another feature of the constellation: the curved line of stars known as the Teaspoon.

Brilliant Jupiter, which reached opposition June 10, leads Saturn and the stars of Sagittarius in their nocturnal journey.

While you’re watching these planets, compare their brightness and color to reddish Antares, the heart of Scorpius, below and to the right of Jupiter. The three objects appear low in the southeast to south at nightfall.

Also at nightfall, the Summer Triangle of bright stars is high in the east. The highest and brightest is Vega, in the constellation Lyra, the lyre. To its lower left is Deneb, the jewel of Cygnus, the swan. Deneb also marks the “head” of the Northern Cross. The third star, Altair, in Aquila, the eagle, is below Deneb and Vega.

In the northwest hangs the Big Dipper. Follow the curve of its handle to brilliant Arcturus, the anchor of kite-shaped Bootes, the herdsman, and principal rival of Vega in the brightness category.

Just east of Bootes hangs the Corona Borealis, or northern crown. Just to the east again is upside-down Hercules; a star map will help you trace his form.

Before you put that chart away, look for Ophiuchus, the snake handler, a large but little-known constellation. Ophiuchus’s snake is a two-part constellation: Serpens Caput, the head of the snake, to the west of Ophiuchus and Serpens Cauda, its tail, to the east. The head should be easiest to find; it’s a small triangle of stars below Corona Borealis.

On Independence Day Earth reaches aphelion, the farthest point from the sun in its orbit, about 94.5 million miles from our parent star. When it’s near aphelion, Earth orbits most sluggishly (relatively speaking). As a result, the Northern Hemisphere gets about five more days of spring and summer than the Southern Hemisphere.

Deane Morrison, with the University of Minnesota, can be contacted at morri029@umn.edu. Find U of M astronomers and links to the world of astronomy at www.astro.umn.edu.

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