Night_skies_08-21

Jeff Green | May 29, 2008

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On the day we call “the Solstice” which is derived from two Latin words translated as “the sun standing still”, namely June 21, the sun appears at its northernmost location in the sky of any time in the entire year. For those who regularly watch its rising in the morning, it is easy to see that its current rising position on the horizon is well north of the due eastern point on the horizon, and those who routinely watch the sun’s setting can equally testify that it now sets a considerable distance north of the western point on the horizon. Maybe over the years these skywatchers have gotten to know those northernmost horizon points where the sun rises and sets, as seen from their front door, or from their backyard, on the day of the June solstice, and they know that, beginning the following day, the sun will rise and set just a slight bit to the south along the horizon, and that process of slowly moving southward will continue for six months. Many people also have noticed that, at this time of the year, for a couple of hours each day, both in the early morning and the evening, slanting rays of sunlight actually shine through the north-facing windows of their houses and cottages. Locally, June’s sunrise times range only from 5:24 a.m. EDT to 5:20 a.m., and sunset times range from 8:46 p.m. to 8:57 p.m. The dates of the year’s earliest sunrise and latest sunset are NOT on the same date, and are also NOT on the date of the solstice. At our latitude, the date of the year’s earliest sunrise is actually June 15 when the sun rises at 5:20 a.m. Locally, the date of the year’s latest sunset is June 27, when the sunset time is 8:57 p.m.

Like May, the month of June brings very long twilights. Locally, evening twilight lasts from sunset until well after 11:00 p.m. throughout the month of June, with the latest “end of twilight” being at about 11:28 p.m. in the week following the solstice. The very first hint of detectable morning twilight is a few minutes before 3:00 a.m. during most of the month of June. During the latter half of evening twilight, we should try to notice the emergence of what are called “the winter stars” in the eastern part of the sky, and particularly the Great Winter Triangle. It is very easily recognized since there are no bright planets in the area. Dominating the eastern evening sky is Vega, brightest star in the constellation Lyra, which has four discernible stars below it, and which the ancients saw as the outline of a musical instrument played by the god Apollo. Below it and to the left is Deneb, the brightest star in the constellation Cygnus the Swan or the Northern Cross, a star pattern seen at various times in history as either a large bird flying southward, or the religious symbol of the cross. Try to see this pattern, which is much larger than the pattern forming the lyre. The third member of the triangle is down and considerably to the right from Vega; it is Altair, the brightest star in the constellation Aquila the Eagle, though the modern observer, with a less active imagination than his ancient counterpart, generally fails to recognize a large bird in the pattern of stars near Aquila. However, it might be interesting for the modern stargazer to try to appreciate something that could not have been known in ancient times: that there is a vast difference in the distances of these three bright stars in the eastern sky. Vega appears brightest of the trio of stars, but it is not the nearest; since modern astronomy recognizes that it is 25 light-years away from Earth. Altair is 17 light-years away, and Deneb is an astounding 1500 light-years away.

Of the five bright planets, only three of them may be seen for most of this month. As evening twilight deepens, reddish Mars appears in the western sky to the left of the twin stars of Gemini, that is, Castor and Pollux. Higher up in the western twilight sky, it will be easy to recognize the second planet of the evening, Saturn and quite near it Regulus, the brightest star in the constellation Leo the Lion (Regulus is the lower one and it is not quite as bright as Saturn). During late May it was easy to see Mars moving away from Gemini and through the constellation Cancer which has few bright stars, and Mars started moving upward and to the left toward Saturn and Regulus. This movement of Mars will continue during all of June – upward and to the left and completely through Cancer and partly through Leo the Lion. Finally, on the evening of June 30 Mars will appear right beside Regulus Remember that what you are watching, night after night, will be the REAL orbital motion of Mars in its orbit around the Sun. Similarly it will be possible to watch the real orbital movement of Saturn also, but because Saturn is so much farther away from Earth, its movement will not appear as dramatic as that of Mars. However, most careful observers will be able to detect Saturn’s movement – upward and to the left and away from the star Regulus over the course of the month. Notice that the orbits of both these planets will appear to carry them upward and to the left as the month goes by; like all the planets, they are in a band of the sky called “the Ecliptic”, which is aligned with the orbit of the Earth around the Sun. Try to observe both these planets every single night, if the weather allows it, and make some drawings of their changing positions, night after night, in reference to the star Regulus. Observers will notice that by the end of June both planets set shortly after the end of twilight, that is, a short while before midnight, and so by then they may need to move to a location where trees or other obstructions do not block the view.

The third planet for the month is the brilliant Jupiter which may be seen rising in the southeast before midnight, with its brightness dominating the whole southern sky for the entire night. Owners of good binoculars or a small telescope may enjoy the views of Jupiter’s four largest moons orbiting the planet, and rapidly changing position from night to night. Venus is now in that part of its orbit when it is on the other side of the sun, and so it cannot be seen at all this month. Mercury may be seen, weather permitting, in the last four or five days of June, very low in the eastern sky about an hour before sunrise, but binoculars may be required to identify it in the glow of twilight.

Several lunar conjunctions will be very worthwhile viewing. In the western evening twilight on June 6 and 7, the thin crescent moon will appear below Mars. On the next evening, June 8, it will form a neat triangle with Saturn and Regulus. Don’t miss that one!! [Note the Moon is also orbiting in the Ecliptic, as mentioned above.] A near-Full Moon will appear just below reddish Antares, on the night of June 16. Also, a “must-see”! Use binoculars that evening! Through the night of June 19, the bright gibbous moon will be drawing nearer to Jupiter – also worth watching with binoculars for several hours! In the hour before sunrise on the morning of June 30, the slender crescent will be seen in front of the famous Pleiades Star Cluster, as both rise in the east. Have a good eastern horizon and use binoculars, beginning at 4:00 a.m.

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.