Nightskies_apr_28

Jeff Green | Apr 28, 2005

Night Skies April 28, 2005

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by Leo Enright

At the beginning of May, in this area, sunset is just after 8 p.m. EDT, and by the end of the month, it is at 8:40 p.m., an average of over one minute later each day. Over the same period, the end of evening twilight moves from 10 p.m. to about 11 p.m., an average of almost two minutes later each evening. In the morning, at the beginning of the month, twilight begins early, at 4 a.m., with sunrise at 6 a.m., but by the end of May, twilight starts just after 3 a.m. with sunrise at 5:30 a.m. As seen from these numbers, on the last day of the month, complete darkness in this area is only from 11 p.m. until 3 a.m., that is, for only four of the twenty-four hours!

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 south-eastern sky. In Leo, the large feline is outlined by a distinctive backwards question mark above the very bright star Regulus and the large triangle of stars to the left, with Denebola as its brightest member. In the middle of the outline of a reclining Virgo is the brilliant whitish star Spica. As you gaze on these three stars, which are among the brightest 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 six 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 hot as our sun and one of them over four times as hot! Remember this the next time you see gleaming Spica among the stars of Virgo in the south-eastern evening sky!

Among the five bright planets, Jupiter still dominates the evening sky and remains visible for most of the night. During evening twilight and the early part of the night, it is by far the brightest object in the south-eastern sky. Those who have a pair of good binoculars or a small telescope can easily see the four largest of its moons changing their positions from night to night as they revolve around the planet. Saturn is fairly high in the western evening sky at the beginning of May, but it will be appear slightly lower each evening, if one observes it at the same time from night to night. Those who are able to observe it carefully with a good pair of binoculars or a small telescope can see not only the system of rings, but also Titan, the largest of its moons as it completes its 16-day orbit around Saturn. Saturn is to the left of the stars Castor and Pollux in the constellation Gemini, and is noticeably brighter than these two stars. Venus, brightest planet of them all, which has not been visible for almost three months, finally does become visible this month, but whether you see it or not, and when you see it, depends on several factors. If you have a very good view of the western and north-western horizon without any trees or buildings obstructing your sight, and if you use binoculars to scan the horizon in that direction from 30 minutes to 60 minutes AFTER SUNSET, you may be able to spot this brilliant object within the first 10 days of the month; you should definitely be able to spot it between May 10 and May 20; and you should be able to see it with the unaided eye between May 21 and May 31. I would be interested in hearing from observers regarding the time and date on which they first see this bright planet. Mercury may be seen only in the early morning during the early part of the month, and only by those who have a good view of the eastern horizon for a short period of time beginning about 30 minutes before sunrise. Reddish Mars may be seen rising in the east at about 2:30 a.m. and it is well up in the south-eastern sky during morning twilight. Its noticeable brightening over the course of this month is an indication of the great performance it will put on later this year.

This month the moon makes several excellent conjunctions with bright planets, giving us some beautiful sights that we should try not to miss. On May 9 during evening twilight, about a half-hour after sunset, those with an excellent north-western horizon may glimpse the thin crescent moon slightly above Venus and the Pleiades star cluster, a very beautiful sight, but one that may require binoculars to see! The following night, May 10, at about the same time, the crescent will be slightly larger, but still a beautiful sight as it appears to the left of the bright start Capella. Two nights later still, on May 12, a larger crescent moon is to be seen just below the stars Castor and Pollux in Gemini, and on the 13th it is just to the left of these twin stars and just above the planet Saturn. On the nights of May 19 and 20, the gibbous moon is in the constellation Virgo, beside Jupiter on the 19th, and beside the star Spica on the 20th, an excellent demonstration of how far across the sky the moon travels in one day. During the night of the Full Moon, May 23 -24, the moon may be seen moving closer and closer to Antares, the brightest star in the constellation Scorpius, and in fact, covering the star, and hiding it for about an hour or more, in an event that is called an occultation. The disappearance of the star, as seen from this area should be at about 4:15 a.m. Once again I would be interested in hearing from anyone in the area who observes the event (whether using binoculars, a small telescope, or the unaided eye) and records precisely the time when the disappearance occurs. Another event well worth observing is the very close approach of Last Quarter Moon and the planet Mars during morning twilight on May 31.

The peak of the well-known Eta Aquarid Meteor Shower occurs between May 3 and 10 with the best chance of seeing bright and fast meteors in the southern sky early in the morning hours of May 5 and 6. If you observe for an hour or more on either or both of these mornings, be sure to record the number of meteors you see each hour.

More information about observing the moon, planets, and other objects of the spring and summer sky is to be found in the book The Beginners Observing Guide which is now available at Sharbot Lake Pharmacy.