Night_skies_apr_07

Jeff Green | Mar 29, 2007

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The Night Skies of April 2007:Brilliant Venus moves past the Pleiades

by Leo Enright

At this time of the year, many skywatchers notice the rapidly changing amounts of daylight that we receive from day to day. With the change to Daylight Saving Time, which occurred on March 11, those changes have seemed even more dramatic than they really are. At the first of April, sunset locally is at about 7:30 p.m. EDT, and at the end of the month, it is a bit after 8 p.m. This change of about 30 minutes in 30 days means, of course, that sunset is about one minute later each day. The end of evening astronomical twilight changes by even more than one minute per evening since it goes from 9:15 p.m. EDT on April 1 to about 10:15 p.m. at month’s end. In the mornings the changes are even greater, with the sunrise times becoming earlier by almost two minutes per day, moving from 6:50 a.m. on the first day of the month to 6:00 on the last day of the month. From this information, it should be easy to calculate sunrise, sunset, and end-of-twilight times for each day of April.

Shortly after sunset and before the end of evening twilight on any clear evening, it is easy to notice that the winter star patterns listed in the past four monthly columns, (Orion, Taurus, Gemini, Canis Major and Canis Minor) are now sinking lower into the southwestern sky, and that the large “spring constellations” have moved up into the southern and south-eastern sky. Most prominent of the spring groupings of stars are two huge ones: firstly, Leo, the Lion, with the familiar shape of a “backwards question mark” forming the head, mane and front paws of the giant feline, and a “right-angled triangle” forming its hind quarters, and secondly, the constellation Virgo, with the brilliant whitish star Spica amid two large rectangular patterns, from which it is somewhat difficult for the modern observer (with a less active imagination than his ancient counterpart) to discern the outline of a young lady carrying a bouquet of flowers. However, experienced modern observers with their telescopes, have been known to spend hours amid the stars of this constellation observing the hundreds of extremely distant galaxies, each one of them with several hundred billion stars, like our own Milky Way Galaxy.

Of the five bright “naked-eye” planets, only three of them may be seen easily this month and one may be seen with some difficulty. In the early evening’s western sky, and in fact, throughout twilight and even after the end of evening twilight, the brilliant planet Venus dominates the heavens on every clear night. Those who spot its spectacularly bright glow right after sunset should be able to watch it for 3 to 3 hours, especially in the latter part of the month, if they have a very good view of the westerly horizon to watch it right to the moment of its setting. As the month progresses, careful observers will easily notice the effect of Venus’s orbit on its position in the sky. From day to day, Venus will appear to move upward among the background stars. Note its position relative to the Pleiades Star Cluster (also called the Seven Sisters). It will be closest to them on April 11, and after that it will appear to move toward the large Hyades Star cluster which forms the ‘Head of the Bull’ in Taurus, and then on to the two stars marking the ‘horns of the Bull’. Saturn is the next planet to be noted each clear evening, high in the southern sky and to the right of Regulus, the brightest star in the constellation Leo, the Lion. Owners of small telescopes have a chance to see Saturn’s rings at a more favorable angle than at any time in the coming five years. The next planet to appear is Jupiter, brighter than any others except Venus. On April 1, Jupiter rises in the east about one hour after midnight, and earlier each night until by April 30 it may be seen rising an hour before midnight. It is not far from the very reddish star Aldebaran, brightest star in the constellation Scorpius. After its rising, Jupiter dominates the eastern sky until almost the time of sunrise. For those who have a very good view of the eastern horizon, reddish Mars may be glimpsed with difficulty low in the eastern sky about 30 to 50 minutes before sunrise, but binoculars may be required to see it in the brightening glow of morning twilight.

The moon, in its orbit around the earth this month, provides several interesting sights as it appears beside the brightest of the planets. On the evening of April 2, the moon, almost exactly at Full Moon, will appear beside Spica, brightest star in the constellation Virgo. On the morning of April 7, one hour before sunrise (see first paragraph), the moon appears in the southern sky below, and to the right from, Jupiter and the star Antares. The following morning at the same time the moon is almost directly below Jupiter. On the morning of April 13, between 30 and 60 minutes before sunrise, those who have an excellent eastern horizon may catch the sight of the crescent moon to the right of Mars, and at the same time the following morning the very slim crescent will be to the left of Mars. On April 18, 19, and 20, in the western evening sky about an hour after sunset, the waxing crescent moon will present a beautiful sight. On the 18th, it will appear below Venus and the Pleiades, on the 19th between Venus and the Pleiades, and on the 20th above Venus. On the evenings of April 23 and 24, the First Quarter Moon will appear to the right of Saturn; on the 25th it will appear to the left of Saturn and slightly to the right of the star Regulus. On the evening of April 30, try to see the moon beside the star Spica, quite close to where it was seen on the evening of April 2 – proof that, in less than 28 days, the moon has returned to the same place among the stars, even though Full Moon will not occur for about two more days, that is, not until May 2. That difference is what astronomers call the difference between the Sidereal Month (less than 28 days - 27.32 to be exact – the time between the moon’s being in the same place among the stars) and the Synodic Month (29.53 days – the time between similar phases, such as two Full Moons, and that difference is caused by the fact the earth is in orbit around the Sun, something we can easily forget, if we are thinking only of the Moon’s orbit around the Earth.

A well-known meteor shower, called the Lyrids, reaches its peak on April 22, and may be well worth watching during the very early morning hours of both Sunday, April 22 and Monday, April 23, beginning after 3 a.m. local time. If the skies are clear, observers can expect to see a few very bright fireballs among the swiftly moving meteors, or “shooting stars”, as they are called by some people.

More information about observing the night sky at all seasons of the year is available in the latest edition of the book, The Beginner’s Observing Guide, now available at Sharbot Lake Pharmacy. Enjoy the beauties of the spring sky!