Stars over Sisters 7/01/2020

In July the warmer weather and increasingly longer nights combine to make stargazing a perfect activity with which to spend your time. Now, if we could only find a way to start observing earlier in the evening and get to bed at a more reasonable hour, it would be ideal.

Of course, doing away with daylight saving time is the obvious solution, but that probably won’t happen anytime soon.

One of the most recognizable constellations in the summer sky is Cygnus, the swan. It is the 16th-largest constellation in the sky, using up 804 square degrees of the celestial sphere. Appearing to fly along the Milky Way, the heavenly bird will be nearly overhead at midnight by mid-July.

Cygnus is bordered by Cepheus to the north, Lyra to the west, Vulpecula to the south, and Lacerta to the east. Its brightest star is Deneb, a blue-white supergiant that is the 19th-brightest star in our sky lying about 1,550 light-years from Earth. Deneb marks the swan’s tail while Albireo denotes its head.

But Cygnus is also known as the Northern Cross. In this case Deneb is the top of the cross while Albireo represents its base. It is interesting to note that the cross seems to stand upright just above the northwestern horizon near Christmas time.

Deneb is the northern-most member of the Summer Triangle. The other two stars that complete the triangle are Vega in Lyra and Altair in Aquila. Besides serving as the head of the swan or the bottom of the cross, Albireo is regarded by many observers as one of the finest and most colorful double stars in the heavens.

Although Cygnus contains only two Messier objects (open star clusters M29 and M39), the constellation is rich with many more deep-sky treasures. One of the most prominent of these is NGC 7000, the North America Nebula, so named because of its striking resemblance to the continent of North America. Classified as an emission nebula, this region of interstellar gas and dust is in the process of forming thousands of new stars. The nebula is large, spanning an area of the sky equal to more than four times the size of the full moon and lies about 1,400 light-years from Earth.

There are many myths about Cygnus and one of the most popular has to do with Leda, wife of King Tyndareus, and the god Zeus. Zeus became infatuated with Leda so, in order to seduce her, he would turn himself into a swan. Leda eventually bore two sets of twins. One set, fathered by Zeus, were Pollux and Helen of Troy, who were immortal. The mortal twins, Castor and Clytemnestra, were born of the union between Leda and her husband King Tyndareus.

On July 4 the earth will reach the point in its orbit that is farthest from the sun, known as aphelion. At that time our home planet and the sun will be 94.5 million miles apart.

The two largest gas giants in our solar system officially become evening objects this month when they reach opposition: July 14 for Jupiter and July 20 for Saturn. When the earth is directly between a superior planet and the sun (opposition), that planet can be seen all night, from dusk until dawn the next morning. Both Jupiter and Saturn will rise earlier as the summer progresses.

The three remaining visible planets, Mars, Mercury and Venus, occupy the morning realm. Near the end of the month Venus in Taurus and Mercury in Gemini can be seen at dawn just before sunrise.

The moon lies in extreme-eastern Libra near the border with Scorpius on July 1. But on each successive day throughout the month, it will move eastward across the sky, ending up in Sagittarius on July 31. During that time, of course, the moon will wax, wane, then wax again as it displays a full range of phases: full moon on July 4, last quarter July 12, new moon July 20 and first quarter July 27.