| Apr 26, 2007

Night Skies

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The Night Skies of May 2007:Venus dominates our May evening sky

by Leo Enright

During the month of May, the amount of daylight steadily increases from one day to the next, but not quite as much as it did in April. As daylight hours increase, so the night-time hours decrease accordingly. At the beginning of May, in this area, sunset is just after 8pm EDT, and by the end of the month, it is at 8:40pm, an average of over one minute later each day. Over the same period, the end of evening twilight moves from 10pm to about 11pm, an average of almost two minutes later each evening. Most serious skywatchers notice that it is a long wait in late May until the sky becomes completely dark. In the morning, at the beginning of the month, twilight begins early, at 4am in fact, with sunrise at 6am, but by the end of May, twilight starts just after 3am with sunrise at 5:30am. The hours of complete darkness are becoming very few! As seen from these numbers, on the last day of May, complete darkness in this area is only from 11pm until 3am, that is, for only four of the twenty-four hours! Use the above information to calculate for yourself the times of sunset, end of evening twilight, beginning of morning twilight and sunrise for each night of the month.


The long evening twilights of May give us an excellent chance to observe the bright stars of the spring constellations as they gradually come into view in the southern sky. As twilight darkens, try to notice the easily-seen patterns of Leo, the Great Lion of ancient mythology, high in the southern sky, and Virgo, the young lady of ancient tales, somewhat lower in the southeastern sky, and of course, well to the left of the great lion. In Leo, the large feline is outlined by a distinctive “backwards question mark” above the very bright star Regulus and a large triangle of stars to the left, with Denebola as its brightest member. In the middle of the outline of the reclining Virgo is the brilliant whitish star Spica. As you gaze at these three stars (Regulus, Denebola, and Spica) which are among the very brightest objects in the spring sky, remember that they are at greatly varying distances. While our sun is 8 LIGHT-MINUTES away from Earth, Regulus is 69 LIGHT-YEARS away; Denebola is 40 LIGHT-YEARS away; and Spica, though easily seen to be much brighter than Denebola, is over 6 times as far away, being no less than 275 LIGHT-YEARS from us. This means that the INTRINSIC brightness of Spica must be incredibly great! Professional astronomers have determined, in fact, that Spica is really two stars, one of them with a surface temperature over three times as great as our sun and one of them over four times as great! Remember this the next time you see Spica gleaming among the stars of Virgo Among the five bright planets, four of them are to be easily found in the evening sky during May with only one postponing its appearance until morning twilight. Venus, this month, actually reaches the peak of its current eight-month evening apparition with its brilliant appearance in the western sky immediately after sunset and remaining visible until it sets over 3 hours later. Many people do not realize how bright this planet it, and that, like the moon, it is bright enough to be seen in the daytime. See for yourself. Become familiar with its location at the time of sunset, and then on the following night, try to locate it at about the same place BEFORE sunset. Small telescope owners may be able to see that Venus has phases, like the moon and over the course of this month, it slowly changes from the shape of a gibbous moon to almost the shape of a first-quarter moon. Also in the western evening sky after sunset, Mercury puts on its best evening appearance of the year in the second half of May. Do not look for it before May 15, but after that date, those with a good view of the western horizon, beginning about 30 to 40 minutes after sunset, may spot this bright object just above the horizon and moving higher each evening. From May 18 until the end of the month, Mercury will be at least 10 degrees above the horizon – that is, the width of a fist held at arm’s length. By the end of the month, Mercury will set about 1 hour and 50 minutes after the sun, giving plenty of time to see it, if one has a good western horizon, and something that will be particularly gratifying for those who may never before have seen Mercury. Saturn continues this month to be visible very high in the southwestern evening sky in the constellation Leo, the Lion, appearing just to the right of the previously-mentioned star pattern known as the “backwards question mark” which outlines the head and forepaws of the giant feline. Very careful observers may be able to note that, during May, the distance between Saturn and Regulus, the brightest star in the constellation Leo – located at the foot of the “backwards question mark” – decreases slightly, as the orbital motion of Saturn around the sun carries it slowly eastward across the sky. Jupiter, which is second in brightness only to Venus, rises in the southeast at about 11pm on the first day of May, and a few minutes earlier each evening until by the last day of the month, it will be seen rising at about the time of sunset. After its rising, its brilliant light dominates the southeastern part of the sky for the rest of the evening, and it may be seen for the rest of the night moving across the sky – just as the earth’s rotation causes the sun to appear to cross the heavens during the daytime. Skywatchers familiar with the constellations will recognize that Jupiter is near the bright stars of the constellation Scorpius with its brightest star Antares seen to the right of Jupiter. Very careful observers mayl notice that, over the course of the month, Jupiter appears to move closer to reddish Antares. Small telescope owners may also notice the four brightest moons of Jupiter change position from night to night – just as Galileo did about 400 years ago when he discovered that Earth was not the only planet with a moon orbiting it. Reddish Mars holds off its appearance until about 2 hour before sunrise when it may be seen rising in the east. Look for it throughout the month low in the eastern sky as dawn begins to brighten that part of the heavens.

This month the moon makes several interesting conjunctions with planets. In the early morning sky on May 12 and 13 the waning crescent moon appears beside Mars – on the 12th to the right of Mars, and on the 13th to its left. On the evening of May 17, a fine challenge will be seeing the splendid sight of the slender crescent moon very low in the western sky. Be sure to try for it starting about 30 to 40 minutes after sunset, if you have an excellent view of the western horizon – such as one over a lake or large body of water. On May 18 also in the western evening twilight, the lunar crescent will be further up and about half-way between Mercury and Venus. During twilight on May 19, try not to miss a VERY spectacular conjunction when the two brightest objects in the night sky (the moon and Venus) are EXTREMELY close, in fact, less than two degrees apart! (A degree is the width of a fingernail held up at arm’s length.) On the night of May 22 the moon is very near Saturn, and on the night of May 23 it is near the bright star Regulus. On the night of May 31 the Full Moon is near the star Antares and to the right of the planet Jupiter, and the following night, June 1, it appears below Jupiter.

The annual Eta Aquarid Meteor Shower reaches its peak on May 5, but the number of those “shooting stars” seen may be less than usual because of the bright moon. However, those who look in the southern sky for an hour or more on the mornings of May 5 and 6 may see a number of bright and fast-moving meteors.

More information about observing the night sky throughout the year is to be found in the book The Beginner’s Observing Guide, now on sale at Sharbot Lake Pharmacy.

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