Night_skies_08-25

Jeff Green | Jun 26, 2008

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The generally warm conditions of our July nights are often the only incentive needed to whet the appetite for stargazing in people. Examples of this are abundant, with vacationers in provincial parks and cottagers on the shores of many lakes nightly spending a couple of hours enjoying the beautiful celestial sights that were not available to them from their homes in cities filled with light pollution. Locally this month, both sunset and end of twilight times arrive earlier by less than one minute per day, with the sunset of July 1 being at 8:45 p.m. EDT, and the sunset of July 31 being at 8:25 p.m.. In the same period, the end of astronomical twilight moves from 11:15 p.m. to 10:50 p.m. Similarly, the beginning of morning twilight times and sunrise times are arriving later, and by about the same amount each day.

As the evening skies darken between 9:00 and 11:00 p.m., the great Milky Way comes more clearly into view and it gradually dominates the eastern half of the sky, sweeping from the northeast to the south. As your eyes move along this broadening heavenly pathway, try to remember that it is really one great arm of our home galaxy, suitably called The Milky Way Galaxy, and it is composed of over 200 billion stars. Our sun is just one of those billions of stars, and our telescopes, even those owned by amateur astronomers, show us that, in all directions in the sky, there are vast numbers of other such galaxies at enormous distances from our own. Follow the Milky Way from the distinctive “W” of the constellation Cassiopeia in the northeast to the constellation Cygnus or The Northern Cross in the east. Surrounding Cygnus, take note, on any clear night, of the three brightest stars in the eastern sky, or The Summer Triangle of Stars – Deneb, brightest star in Cygnus (The Swan), on the left of the triangle; Altair, brightest star in the constellation Aquila (The Eagle), well to its right; and finally above the Milky Way, the brightest of the trio, Vega, a truly brilliant white star in Lyra (The Lyre). Continue along the Milky Pathway to the constellation called Sagittarius in the south, but remember that, to the modern eye, this constellation does not look like an Archer at all, but rather like a simple teapot with its handle to the left and its spout to the right – the reason why many modern books describe it simply as the “Teapot of Sagittarius”. Pay particular attention to this part of the Milky Way, since it is the central core of our galaxy with many billions of stars, and according to many astrophysicists, a black hole which swallows up stars and allows not even light to escape from its grasp.

Among the five bright planets that are normally seen with the unaided eye, only four of them will probably be seen by many observers this month, since Venus, though technically possible to see in the evening shortly after sunset at the very end of July, will be extremely difficult to detect. Both Mars and Saturn will continue the movement they showed last month, but to enjoy their “planetary dance” this month, be sure to have a good view of the western horizon in the two hours after sunset – no trees or buildings blocking your view to the west! At that time on Canada Day, you will see reddish Mars just barely above the star Regulus, brightest star in Leo The Lion. Above it and to the left, by less than the width of a fist held at arm’s length, will be Saturn, which is brighter than Mars. Note their positions carefully, since over the coming 10 evenings, you will be able to see Mars move upward away from Regulus and closer to Saturn. On July 10 Mars and Saturn will appear side by side. Of course, in reality, Saturn is much farther away from us than Mars. They are merely in alignment, as seen from Earth. After July 10, Mars will appear ABOVE Saturn, and continue to move upward. Mars has been in the news recently because of the discovery of frozen water on, and near, its surface. This is the real orbital motion of Mars around the Sun that you are watching this month.

The great king of the southern sky this month will be the planet Jupiter, the solar system’s largest planet. There will be no mistaking it since it will be the brightest by far of the four planets seen this month, and after it rises in the southeast during evening twilight, it will dominate the southern skies all night long. Owners of good binoculars or a small telescope who observe it near midnight will easily see the four largest of its many moons, as Galileo saw them 400 years ago, and they may even see “bands” and “belts” in the planet’s clouds.

The fourth planet to be seen will be Mercury, which may be seen low in the east beginning about 90 minutes before sunrise. As the month progresses it will become brighter, but will be visible for a shorter period of time, and after July 20 it will be very difficult to observe.

Several striking lunar-planetary conjunctions will be well worth observing this month. On the evening of July 5, at about 45 minutes after sunset, don’t miss the view of the thin crescent moon just below the alignment of Saturn, Mars and Regulus. On the following evening, July 6, at the same time, the Moon will have moved upward and will appear slightly below and to the left from Saturn and Mars. On the night of July 16, the Full Moon will be very close to Jupiter, and by watching this pair all night, one can easily observe the Moon’s actual orbital motion over a period of four or five hours.

A meteor shower known as the Delta Aquarids reaches its peak on July 27, but a good number of fast “shooting stars” may be observed from July 26 to 29, with perhaps the best chances of seeing them being after midnight. Observe the southern and eastern sky, and record the numbers seen per hour.

More information about observing the spring and summer sky is available in the book entitled “The Beginner’s Observing Guide” which is now available at Sharbot Lake Pharmacy.