| May 31, 2007

Night Skies

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The Night Skies of June 2007:Venus andSaturn converge in theJune sky

by Leo Enright


June, as always in this part of the world, brings the longest days and the shortest night of the whole year. On the day that is called the “solstice” (which means ‘the sun standing still’), June 21, the sun appears at its northernmost location in the sky of any time during the year. If we watch its rising over the eastern horizon on any of the mornings this month, we can easily see that it is well north of the eastern point on the horizon, and similarly in the evenings its setting is well north of the western point on that horizon. In fact, during June, for a couple of hours in both early morning and late evening, rays of sunlight actually do shine in the north-facing windows of their houses. The times of earliest sunrise and latest sunset are NOT on the date of the solstice, but very dependent on latitude where one lives. Here in Eastern Ontario, the earliest sunrise is June 15 at 5:21 a.m. EDT, one whole minute earlier than sunrise on the 21st, and here our latest sunset is on June 27 at 8:54 p.m. EDT, over a minute later than sunset on the solstice. The day-to-day change in sunrise and sunset time in the month of June is only seconds. June always brings us very long twilights – periods of time in very late evening and very early morning when the sun is below the horizon but the sky is not completely dark. In fact, in June, the first hint of morning twilight begins before 3:00 a.m. for most of the month. Evening astronomical twilight lasts until after 11:00 p.m. every single night of the month, with the latest being about 11:20 p.m. in the last 10 days of the month. In other words, at this latitude in late June, there is a totally dark night sky for only about 3 hours, that is, from the end of evening twilight at about 11:20 p.m. to the beginning of morning twilight at about 2:55 a.m..

For the first half of this month, four of the five bright planets put on an outstanding evening display, with one planet making its appearance after 2:00 a.m. In the later half of the month, one of the planets disappears, but the others continue their performance. On any moonless night in June, the first object to appear in the western sky right after sunset is Venus, by far the brightest of the planets. Careful observers will notice that as the month progresses, it becomes even brighter, and that it is bright enough to see in daylight if one knows exactly where to look, and they will also notice that, late in the month, its apparent height above the western horizon is less than half what it was at the beginning of June. Even more importantly, they may notice two other facts. Venus is moving rapidly in its orbit around the sun, and this month it appears among the background stars of three different constellations. On the first 3 days of the month it is among the stars of Gemini, appearing to make an almost straight horizontal line with the stars Castor and Pollux, the two brightest stars in the constellation Gemini. During the evenings of mid-June, Venus may be seen moving among the stars of the constellation Cancer, and in fact, on the evenings of June 12 and 13, it is very close to the beautiful star cluster known as the Beehive Cluster which is right in the middle of that constellation. If the brightness of Venus is so overpowering that you cannot see the star cluster nearby on those two evenings, just use binoculars, and you will quickly see the rich star cluster. In the last week of the month, Venus is seen among the stars of the constellation Leo, the great lion, and to the right of that constellation’s brightest star Regulus, near which the planet Saturn has been seen over the past four months. As noted in the previous two months, Saturn has been seen to the right of Regulus (by about the width of a clenched fist held at arm’s length) in the western evening sky and it continues to be probably the second bright object that observers will see in the evening twilight (not counting the moon if it is present). Not only does Venus appear near Saturn in late June, but on the evening of June 30, the two planets are only 2/3 of a degree apart – somewhat less than the width of a fingernail held at arm’s length. Don’t miss that evening’s spectacle of two bright planets in such a close conjunction. It is a relatively rare event.Readers with a small telescope will be able to see the changing appearance of Venus as it moves among the stars of those three constellations; the size of its disk will get larger from night to night, and the phase of Venus, like that of the moon, will change from a “first quarter” appearance in early June to a “crescent phase” in late June. The third planet to be seen in the evening sky is Mercury, well down and to the right from Venus during the first ten days of the month. Binoculars will be helpful in finding it in the twilight 30 to 50 minutes after sunset. (When I observed it in late May, binoculars were very helpful in finding it on some evenings; on other evenings it could readily be seen without optical aid.) Remember you will need a good view of the horizon in that direction.

Within an hour of sunset, all observers on any clear night in June should easily see our fourth planet, brilliant Jupiter, the second brightest of the planets, shining in the south-eastern sky. This is a planet that people can follow for the entire night. If they have a small telescope, they may watch the four largest of its moons, hour by hour, change position as they orbit this giant planet. Reddish Mars rises in the east at about 3:00 a.m. in early June and before 2:00 a.m. in late June.

Although, this month, we may not have a Moon-Venus conjunction quite like the one of May 19, we will still see a number of interesting conjunctions. In the western evening sky on June 17, 18, and 19, try to watch the waxing crescent move past Venus and Saturn. In twilight on the 17th, the moon is below Venus; on the 18th, it is between Venus and Saturn; on the 19th it is above Saturn. In the southeastern sky during twilight on June 27 and 28, the almost-Full Moon will be seen moving past the planet Jupiter and reddish Antares, the brightest star in the constellation Scorpius. On the 27th the moon appears to the right of those objects and on the 28th it appears below them.

Doubtless, some newspapers and other media will try to make a story out of the fact that, on June 30, we will have the second Full Moon of the month, something they will call a “Blue Moon”. Such an “event” has absolutely no special astronomical significance. Any phase of the moon is repeated on average 29 days later. Hence, with months of 30 or 31 days happening 11 out of 12 times a year, the chances of one of the four “common phases” repeating in some month of the year is fairly good, and the “Full Moon” phase will definitely be repeated in some month about once every two or three years. NOT A RARE EVENT! This “urban legend” defining a “Blue Moon” as a second Full Moon in a month is based on a misunderstanding of some calendar rules and on a question on one of the versions of the board game called ‘Trivial Pursuit’.

For more information about the summer sky and objects to observe in it, a good introductory book with star maps is available locally: The Beginner’s Observing Guide, which is on sale at Sharbot Lake Pharmacy.

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