Few people have had the privilege of contemplating the slow passage of Venus across the face of the Sun. Though the last transit of Venus occurred on June 8, 2004, the two before that took place in 1882 and 1874. And to see the next one, you’ll have to wait until December 11, 2117 — that’s more than 105 years!
Now you know why astronomers are so excited and enthusiastic about this transit. Astronomy clubs throughout Québec are organising observing sessions, in order to share this extraordinary event with the public at large. At the same time, measures are being taken to stress the need for safe solar observing, done with specialised instruments and proper solar filters. You can consult transitofvenus.ca for more information on this phenomenon, and the best way to observe it.
Transits of Venus require the involvement of three celestial bodies — Earth, Venus and the Sun — all of which must lie in a straight line, more or less. When in this configuration (that is, between the Earth and Sun), Venus is said to be at inferior conjunction. Inferior conjunctions of Venus occur every 584 days, but since Venus’s orbit is inclined with respect to Earth’s, the planet usually appears either above, or below, the Sun’s disk. Perfect alignments only occur when Venus is at inferior conjunction near one of its orbital nodes — that is, where the orbit of Venus intersects Earth’s orbital plane. Such an alignment will take place on June 5, 2012. As a result, for several hours, Venus will pass directly in front of the Sun’s disk.
Unfortunately, for observers in North America, only the beginning of the transit will be visible. For all regions of Québec, it will start around 6:03 P.M., EDT. At the moment of first contact, the Sun will already be low on the west-northwest horizon. During a two-hour period, observers will see Venus slowly crossing in front of the Sun — until sunset ends the show. Those who are lucky enough to be in the Pacific, Australia, Japan, Russia and Alaska, will be able to witness the transit in its entirety.
A trio of planets
The end of June offers some wonderful opportunities to observe the planets. Mercury, which is always a challenge to find, will be a choice target at month’s end. On June 21, in the glow of twilight, a thin crescent Moon will be positioned just to the left of the tiny planet, which will make it easier to spot. Look above the west-northwest horizon, about half-an-hour after sunset, for a chance to see it.
Mars and Saturn have been visible in the starry sky for several months now, and their presence continues in June. The two planets are somewhat faint, and shine with about equal brightness, which could make them difficult to distinguish from the surrounding stars. Luckily, a gibbous Moon will be on hand to help, during the closing days of the month: Look for the Moon near Mars on June 26, and near Saturn on June 28.
For early risers, a thin crescent Moon will shine next to the bright planet Jupiter, above the east-northeast horizon at dawn, on June 17: This promises to be a superb show. And Venus, which passed in front of the Sun on June 5, will join Jupiter toward the end of the month. More about that next time…
Those who are anxiously awaiting the warmth of the summer Sun, will be pleased to note that the summer season begins, here in the northern hemisphere, on the morning of June 20, at precisely 7:09 A.M. EDT. For astronomers, however, this period represents a reduction in activities; since nights are short, observations are curtailed: They are looking forward to the autumn months.