| May 28, 2009

Back to HomeNight Skies - June Morning dance of planets and a lunar occultation

by Leo Enright

June means long days and short nights. On the June day that we call the solstice, June 21, the sun appears highest in the southern sky at noon for people at northern latitudes and it appears furthest north along the eastern horizon where it rises and along the western horizon where it sets. That term ‘solstice’ derives from two Latin words whose English translations are ‘the sun’ and ‘standing still’, and the word is suitable to describe what is observable on that day if the skies are clear. Our skywatching ancestors learned over thousands of years that it was the day when the noonday sun would soon start to move downward from its greatest height, and the rising and setting sun would soon start to move southward again from their northernmost points along the eastern and western horizons. Those who are able to have a good view of the horizon for the rising and setting sun can easily verify that the sun’s position on both the easterly and westerly horizons at the moment of rising and setting is, at that time, a considerable distance north of both the true east and true west. Related to that fact is the fact that, for several hours in both early mornings and late evenings in late May and in June, rays of sunlight actually shine through the north-facing windows of our houses. Locally, June’s sunrise times range only from 5:24AM EDT to 5:20AM, and sunset times range from 8:46PM to 8:57PM. It may be a great surprise for many people to know that the dates of the earliest sunrise and the latest sunset are not on the solstice and are not on the same date at all. Those dates vary considerably with one’s latitude. At our latitude, the date of earliest sunrise is actually June 15 – at 5:20AM, which is a whole minute earlier than sunrise on June 21. (The day-to-day difference in sunrise and sunset times in June, and in December, is only seconds – much different from other times of the year.) Locally, latest sunset is on June 27 – at 8:57PM, when it is a whole minute later than it is on June 21.

Like May, June also brings very long twilights in this part of the world – those periods of time when the sun is below the horizon, but the sky, especially the eastern sky in the very early morning and the western sky in the very late evening, is not dark enough to see all the stars that can be seen. Locally, evening astronomical twilight lasts until well after 11PM in all of the month of June, with the very latest end of twilight being at 11:28PM in the week following the solstice. The very first hint of morning twilight may be detected a few minutes before 3AM during most of June. In other words, in this part of the world in June, there is a totally dark night sky for only about 3½ hours each night.

The huge spring constellations, Leo the Lion, and Virgo the Maiden, which we saw dominating the southern sky for the past three months, are now sinking in the west in the late evenings of June. The distinctive pattern of Scorpius the Scorpion is seen climbing up from the south-eastern horizon, and to its right is the constellation Libra the Scales – much less distinctive, with only four bright stars, one of which is definitely greenish – an extremely rare colour among the stars of the sky. Be sure to locate this oddity on any clear night in June.

In the evening sky this month, the only bright planet visible is Saturn, which continues to be seen in the west among the bright stars of Leo the Lion, in fact, to the left of the distinctive triangle of stars that our ancient ancestors saw as forming the hindquarters of the great beast. Owners of small telescopes can still have a good view of Saturn’s rings and several moons, but the planet is setting earlier each night and by late June will be very low by midnight. The second bright planet to be seen will be Jupiter, which appears among the stars of the constellation Capricornus as it rises in the south-east about midnight. Owners of small telescopes who wish to view Jupiter’s moons should wait until about 3AM when it is high enough to allow a clear view of the planet. Venus, Mars and Mercury are to be seen low in the eastern sky during morning twilight. Be sure to have an unobstructed view of the eastern horizon. Dazzlingly bright Venus and reddish Mars are very low in the east in early June and somewhat higher later in the month. They appear to perform a dance around each other with Mars waltzing from the lower left of Venus in early June to the upper right in late June. Their closest approach is on the morning of June 21 when they appear separated by only two degrees – twice the width of a fingernail held at arm’s length. Mercury, appearing farther away from brilliant Venus than Mars, will be more difficult to spot. Mercury will be lower than the Venus-Mars duo and to their left and fainter than Mars in early June. By late June it will be brighter than Mars. Try to spot it after June 15. If Mercury is not seen naked-eye at the position given between 60 and 30 minutes before sunrise, use binoculars to find it, but be sure to put them aside before sunrise to avoid the danger of looking at the sun.

Several lunar-planetary conjunctions will be well worth observing. On June 13 and 14, the gibbous moon will appear near the planet Jupiter in the southeastern sky – best seen between 1AM and 3AM each morning. Seeing them both mornings will be a lesson on how far the moon appears to travel across the sky in one day. In the morning twilight of June 19, 20, and 21, make a point to watch the slim crescent moon march past three planets and the Pleiades Star Cluster. On the 19th, the moon is just above the Venus-Mars duo mentioned above; on the 20th the crescent is just above the Pleiades and further above Mercury; on the 21st, the extremely thin crescent is to the left of Mercury and very low in the sky. In the western evening sky after sunset on June 26, watch the waxing crescent to the left of Regulus and on the 27th to the left of the planet Saturn. To avoid missing any of the above events, mark the dates on your calendar.

On the evening of June 6, a very special event occurs involving the moon and Antares, the brightest star in the constellation Scorpius. As seen from some locations in Canada, the moon will move in front of the star for what is called an occultation and hide the star for a period of time, and as seen from other places, the moon will appear to “just miss the star”, but move very close to it. For example, the current best predictions are that Toronto will have an occultation, but Ottawa will have a “miss”. What will your location have? It depends on where you live. Get out your binoculars and CAREFULLY observe the moon and the bright star near it, at its northern limb – starting at about 10:45PM. The occultation MAY occur between 10:55 and 11:15PM. Record exactly IF it occurs, and for EXACTLY how many minutes the star disappears. I would be most interested in hearing the results.

More information about observing the spring and summer sky is available in the book entitled “The Beginner’s Observing Guide” which is now available at Sharbot Lake Pharmacy and on the internet at www.rasc.ca/publications.

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