Night_skies_June_2004

Feature Article April 29

Feature Article June 3, 2004

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The Month Of A Rare Venus Event

During the month of June, in this part of the world we always have our longest days and shortest nights. We also have what we used to call the summer solstice. It is now more properly called the June solstice, since for our friends in Australia and other southern countries, it is almost mid-winter, not mid-summer. If we watch the sun rising and setting this month, we can easily see that it is well north of the eastern point on the horizon when it rises and well north of the western point on the horizon when it sets.

For years many people, in fact, have noticed that, for a couple of hours each day, both in the early morning and in the evening, the rays of sunlight shine through the north-facing windows of their houses. Also, the times of our earliest sunrise and latest sunset (something that is quite surprising to many people) are very dependent on the latitude where one lives, and are not precisely on the date of the solstice. At our latitude, the earliest sunset of the year is at 5:20a.m. EDT on June 15th, six days before the solstice and the latest sunset is at 8:57p.m.on June 27th, six days after the solstice.

However, over the whole month of June the day-to-day change in the sunrise and the sunset times is very small, often a few seconds, rather than the whole minute or two minutes that we have in the day-to-day differences at the times of the equinoxes.

June also brings, at this latitude, extremely long twilights those periods of time when the sun is below the horizon but the sky is not completely dark. Locally astronomical twilight does not end until about 11:10 p.m at the beginning of the month and almost 11:30 at months end. The first hint of astronomical twilight in the morning occurs between 2:50 and 2:55 a.m. during most of the month. In other words, there is a totally dark night sky for only about 3 hours during the entire month.

Fortunately even during the darker parts of twilight, we can see the brighter stars and planets, and often in the case of the bright planets, when studied in small telescopes, their images are more pleasing in twilight, since the brightness then is not so overwhelming as to destroy the subtleties of viewing them. During the latter half of our evening twilights, we can now enjoy the view of the three bright stars of the Great Summer Triangle (brilliant Vega in the constellation Lyra, Deneb in Cygnus, and Altair in Aquila) emerging in the eastern sky, and a bit later, the appearance of the Milky Way weaving its way through this great triangle.

Regarding the bright planets, the sky is far different from a year ago when Mars was becoming the centre of attention and brighter than it had been in many years. This month Venus is, undoubtedly, the centre of attention, but three, and perhaps four, other planets will be easily visible and their changing relative positions will be very noteworthy. Venus, the planet that has been so brilliant over the last eight months that it can often be seen in the daytime if one knows exactly where to look for it, can be seen low in the western evening sky for about an hour after sunset on the first four or five days of the month.

On June 8th, Venus crosses in front of the sun and may be seen on the other side of the sun for about the next eight months. That means that it will be start to be seen in the eastern morning sky before sunrise. The great challenge will be to see how soon one can see it after June 8th. Probably with clear skies and a very good view of the eastern horizon, some people will be able to see it by June 15th, or even before, if they scan the horizon about a -hour before sunrise.

Its visibility time will increase rapidly until by months end, it will be very easy to see Venus beginning 1 hours before sunrise and almost until sunrise. The second-most-brilliant planet, Jupiter, continues to be seen high in the southwest in the late evening twilight to the left of the star Regulus in the constellation Leo. Jupiters very slow movement eastward from that star may be detected by careful observers.

In early June, note that reddish Mars is found below the stars Castor and Pollux in the constellation Gemini low in the western evening twilight. On June 19th, it is in a straight line with them; after that it is above them. This movement of Mars is very easy to notice. Below Mars is a much brighter Saturn, but Saturn will be so low in the twilight after June 20th that it will be almost impossible to see. Try to spot the thin, but waxing, crescent moon 45 to 60 minutes after sunset on these dates: June 18th just to the right of Saturn, June 19th between Saturn and Mars, June 20th above Mars, and June 23 beside Jupiter. With good weather and a good view of the western horizon, Mercury may be seen very low in the west below Mars, from 45 to 60 minutes after sunset between June 26th and June 30th.

The rare Venus event of June 8th is called a transit. Because of the angle of the Venuss orbit around the sun relative to Earths orbit around the sun, on most occasions when Venus passes from one side of the sun to the other side, as viewed from Earth, it passes above or below the sun. An actual passage of the planet across the face of the sun, called a Venus Transit, last occurred in 1882, about 122 years ago. Only 6 Venus Transits have occurred since the invention of the telescope in 1610, and in the 17th and 18th centuries the observations of such events were regarded as important in order to help in calculating the distance between the sun and all the planets.

Probably few people in Ontario will see this event because of when it occurs and where its visibility is possible. The six-hour event begins on June 8 at 1:13 a.m EDT. and ends at 7:26 a.m. Of course, locally the sun does not rise until 5:21 a.m.; therefore, locally there are only about 2 hours to view it, with the sun very low, near the eastern horizon. (Those who want to see the entire event have made plans to go to Europe or Africa.) Venus will appear as a very small, black dot crossing the face of the sun, near the southern edge of the suns disk. As always when speaking of observing the sun, a warning of the extreme danger of eye damage must be given. It is always dangerous to look at the sun, always. It is especially dangerous to do so with unfiltered binoculars or telescope; instant blindness can be the result. What is safe is using a piece of # 14 (NOT #10 or #12) arc welders glass available from arc welders supply shops for a few dollars, or the commercially prepared eclipse glasses with opaque mylar, if one is certain that there are no pin-holes in them. The expensive solar filters made for telescopes, and properly installed, are also safe. (However, all homemade concoctions, like photographic film, smoked glass, beer bottles, or sunglasses of any brand or make ARE NOT SAFE and MUST NEVER BE USED.)

For several reasons, I do not expect that many people will be able to witness this event, except for what they may see on television or the Internet, but they should be aware of it, because of the interest that it will generate. More information about such transits and about other aspects of astronomical observing may be found in the latest edition of the book, The Beginners Observing Guide, which is now available at The Valley Book Shop in Perth and at Sharbot Lake Pharmacy.