Night_skies_jul07

Jeff Green | Jun 29, 2006

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TheNightSkies of July, 2006:Planets & Meteors and a Lunar Occultation

by Leo Enright

The pleasantly warm conditions of July are often an incentive for stargazing. Examples of this interest in the heavens may be seen on almost any clear night of the month when vacationers and cottagers spend a few minutes or a couple of hours enjoying beautiful sights that were not available to them from cities filled wit light pollution. Suddenly the vistas of a vast universe are opened up – a whole wonderful cosmos that can be seen only after sunset. Locally in July, sunset and the end of evening twilight arrive earlier by a bit less than one minute per day, with sunset on July 1st being at 8:45 p.m. EDT and on July 31st at 8:25 p.m. The end of astronomical twilight on July 1st is at 11:15 p.m. and on July 31st at 10:50 p.m. Similarly in the mornings the beginning of twilight times and the sunrise times are arriving later, by about the same amount each day.

Under very clear, dark, rural skies, the great Milky Way is a dominating feature of the late evening twilight, as it sweeps from the northeast to the south. Remember, as you look at it, that you are seeing one great arm of our home galaxy, which is known as The Milky Way Galaxy, and that our Sun is just one star among those millions of indistinguishable stars you see in the Milky Way. Astronomers tell us that there are over 200 billion stars in this galaxy and our telescopes, even those of an amateur astronomer, show us that there are vast numbers of galaxies to be seen. Again astronomers tell us that there are countless billions of galaxies in our incredible universe. As our glance sweeps southward over the Milky Way, we may notice it thickening as we approach the area of the southern constellation that, on star maps, is called Sagittarius. To the eye of a modern observer, it looks not at all like an Archer with a sheaf of arrows, but much more like a simple teapot with its handle to the left (east) and its spout to the right (west). Beginning observers should learn to find (above the southern horizon) and recognize this “Teapot of Sagittarius” every clear summer evening, and they should remember that here in this Sagittarius Star Cloud, where the Milky Way is thickest of all, is the central core of Milky Way Galaxy. It has many billions of stars and probably in its very centre, astronomers tell us, there is black hole which swallows up stars and does not allow even light to escape from its grasp.

Among July’s bright planets, Jupiter will surely be the first one seen by most observers in the evening twilight. As was the case last month, the solar system’s largest planet, Jupiter, is seen shortly after sunset well up in the southern sky, and later in the night in the southwest. Readers may recall, if they observed it carefully in the past two months, they saw it move to the right, or westward, and away from the bright background star called Zubenelgenubi, brightest star in the constellation Libra. This westward, or retrograde, motion of Jupiter ends on July 6th, and for the next several months Jupiter’s motion will again be to the left, or eastward, among the background stars. Noticing this change in direction of its motion will need careful observation, but it should be detectable by the latter part of July. Saturn, during the first half of July, may be seen low in the west beginning about 40 minutes after the sun sets, but after mid-July, it will be quite difficult to see Saturn at all. Binocular users will be able to see it very low in the twilight for a longer than “naked-eye” viewers. Reddish Mars, now fainter than in previous months, is also low in the western evening sky and may be seen above, and to the left, from Saturn. Just as Mars appeared very close to Saturn last month (on June 17th, to be exact), Mars will appear very close to the distant background star Regulus, the brightest star in the constellation Leo on July 22nd. Try not to miss the view of these two objects, apparently so close (less that the width a fingernail held at arm’s length. Remember they will be just above the western horizon about 40 minutes after sunset. Use binoculars to be sure of seeing them. (Obviously they are not really close. The background star is countless thousands of time further away from us than the planet.) Mercury may be seen for only a few days at the beginning of the month, very low in the west, down and to the right from Saturn, for a short while beginning about 30 minutes after sunset. Those who try to observe it should definitely use binoculars and be sure that they have an excellent view of the western horizon. Brilliant Venus continues this month to be visible only during morning twilight low in the eastern sky, a very special reward for those who rise before the sun and look eastward for this “beacon of light” casting its glow on the landscape before the sun rises.

The Moon on its orbital path around the earth this month provides several interesting sights. The most important, and probably most memorable, sight for those who can catch it will be the lunar occultation of most of the stars of the Pleiades on the morning of July 20th. This means that the moon will actually move in front of some of the bright stars of this very famous cluster that is often called The Seven Sisters. To see this event which some readers may have never seen before, they should start observing at about 3:00 a.m. EDT, and use binoculars, if possible, to record the times when the three brightest stars of the cluster disappear as the Moon moves in front of them. Even more interesting to watch will be the reappearance of these bright stars as the Moon moves on in its orbit, because the reappearances will occur along the “dark edge of the moon”. Two mornings later, on July 22nd, the early morning eastern sky will feature a slim crescent moon just above the planet Venus , and the following morning, July 23rd, will have an even thinner crescent Moon just to the left of brilliant Venus. These two events are visible in morning twilight. On the evening of July 26th, just 40 minutes after sunset, try to catch the very slim waxing crescent moon low in the western sky just to the right of Mars and the star Regulus, brightest star in the constellation Leo the Lion, and at the same time the following night, July 27th, try to see the Moon’s slender crescent just above Mars and Regulus. Again use binoculars, if possible, for these two events, and be sure to have an excellent view of the western horizon.

Though it may not be as famous as the Perseid Meteor Shower which reaches its peak in August, the Delta Aquarid Meteor Shower whose peak is in late July is regarded as one that may be quite favourable this year, if the weather cooperates. Best prospects of seeing this meteor shower will be for those who observe between 3:00 and 4:00 a.m. on July 27th, 28th and 29th and generally look to the eastern half of the sky for these “shooting stars”. I am interested in hearing reports of numbers of meteors seen per hour on those dates.

Much more useful information about observing and enjoying the summer sky is to be found in a popular, easy-to-understand book called The Beginner’s Observing Guide, which is now available at Sharbot Lake Pharmacy.