||The Night Skies of July, 2005
The Summer Milky Way and A Group of Bright Planets
The pleasant nights that we usually enjoy in July are often an invitation to otherwise reluctant people to observe the starry summer sky and the bright planets. This may happen on any clear night when people can get away from the glare of street lights and the other forms of light pollution that so frequently interfere with the natural views of the heavens and the precious treasure of our vast universe, so much of which can be seen only after the sun sets. Locally, July’s sunset times range from 8:45 p.m. EDT on July 1 to 8:25 p.m. on July 31. Over the same period, the end of astronomical twilight goes from 11:15 p.m. to 10:50 p.m.
High in the late evening sky this month is the great Milky Way. Remember that our sun is just one star among those 200,000,000 000 (200 BILLION) stars that form this huge galaxy, and our Milky Way Galaxy is just one among the billions of galaxies that are known to exist in our universe. As our eyes sweep southward along that pathway of stars, we can see that the Milky Way becomes thicker as we get closer to the southern constellation that is called Sagittarius on the star maps, though to the modern observer, it looks not at all like an Archer with a sheaf of arrows, but more like a simple teapot with its handle to the east, or to the left, and its spout facing westward, or to the right. Here, in the direction of this constellation that rides above the southern horizon, the Milky Way appears at its thickest, and this thickness is actually the central core of our Milky Way Galaxy, where we are actually looking at billions of stars whose individuality is indistinguishable, as their collective brightness, seen under dark rural skies, makes them look like a distant fire.
Among the planets, the two brightest, Venus and Jupiter, will probably pop into view at about the same time this month, that is, about 15 to 20 minutes after sunset, though some people may notice them even before that time. At that time, Venus will appear low in the sky and above the west-northwestern horizon by just a bit more than the width of a fist held at arm’s length. That is why it is very important to have a very good view of the northwestern horizon to see the brightest planet of them all. For those who have a good view of the northwestern horizon, Venus will set about an hour after it is first seen. Jupiter will be seen higher in the southwestern sky and soon after it is first spotted, the bright star Spica, brightest star in the large constellation Virgo, will appear to the left of Jupiter, and a while later, some of the other stars of that constellation will also appear. Jupiter will set in the west at about midnight, even before that time in late July. Readers of last month’s column should be well aware of the planetary activity that took place very near the planet Venus, and should have enjoyed the fascinating “dance of the planets”, Mercury and Saturn, as they changed positions from night to night beside Venus. This “dancing activity” continues for part of the July, but binoculars will be required to view these other two planets. Remember NOT TO USE the binoculars until after sunset, because of the danger of accidentally looking at the setting sun. For the FIRST TEN DAYS of July, when observed between 30 and 60 minutes after sunset, Saturn should be easily found in the binoculars between Venus and the horizon. At the first of the month, it will be about half-way between Venus and the horizon; each evening after that, Saturn will be seen a bit closer to the horizon and a bit more to the right – until about July 10th or 11th, when it will disappear. In the binoculars, when viewed from 30 to 60 minutes after sunset, Mercury will be appear brighter than Saturn and just a bit to the left of Venus on July 1st, and as it is observed each evening, it will appear lower and lower in the sky, moving downward from Venus and toward the horizon – until it will also disappear about July 22nd. The cause of this apparent changing separation of Venus and Mercury is the real orbital motion of these two planets around the sun – and also the real orbital motion of our planet Earth around the Sun. On the nights of July 21st to 23rd, do not be confused by an object that appears very close to Venus. It is the very distant star Regulus, brightest star in the constellation Leo, the Lion, NOT the planet Mercury, which is much lower and quite close to the horizon on those dates. Once again, remember to have a very good view of the northwestern horizon in order to make these observations. Mars observations are for those who can observe after midnight. This reddish planet rises in the east at about 1:30 a.m. and is at its highest in the southeastern sky as morning twilight starts to flood the landscape. Mars is brighter than it has been over the past few months, and during July it becomes even brighter, a hint of the increasing brightness that will continue during late summer and autumn.
The moon’s orbital motion around the earth this month will bring it into some interesting apparent conjunctions with bright planets. The first one will be a real challenge, namely trying to see the very thin crescent moon just above Saturn and very low in the west-northwestern sky about 30 to 45 minutes after sunset on July 7th. Be sure to choose a site that gives a very good view of the western horizon, and be sure that the lenses of your binoculars have been carefully cleaned. On July 8th, the still-thin crescent may be seen just above Venus and Mercury, between 30 and 60 minutes after sunset. (Using binoculars will allow you to see Mercury as well as the moon and Venus.) On the evening of July 13th, do not miss seeing the First Quarter Moon almost mid-way between Jupiter and the bright star Spica. The following evening the moon is to the left of Jupiter and Spica. On the night of July 17th-18th, the moon appears very close to the bright reddish star Antares, brightest star in the constellation Scorpius. In fact, at 1:00 a.m. that night the moon’s North Pole appears almost to graze the distant star. Use a small telescope or your binoculars to watch the moon’s North Pole glide past the star over a period of a half-hour or more. You will be seeing the real orbital motion of the moon around our planet Earth. In the very early morning of July 27th, the Last Quarter Moon appears to the right of Mars, and the following morning it is to the left of Mars. Also in the morning sky, on July 30th, the waning crescent moon appears not far from the famous star cluster, the Pleiades, a very beautiful sight in the eastern sky.
For more useful information about observing and enjoying the summer sky and all it has to offer, a popular, information-filled book, The Beginner’s Observing Guide, is now available at Sharbot Lake Pharmacy.