Two solar events

Ken Tapping, May 9, 2012

In the sky this week…

  • Venus still dominates the western sky after sunset.
  • Mars is high in the South; Saturn is in the eastern sky.
  • The Moon will reach Last Quarter on May 12.

This month there will be an annular eclipse of the Sun and in June an opportunity to see a transit of Venus across the solar disc. If you have never seen one of these it is likely to be the last chance you’ll get in this lifetime, the next will be in 2117.

The eclipse of the Sun and the transit of Venus will involve observing the Sun. If you are not absolutely sure you know how to do this, get into contact with someone who does. The solar disc is very bright, and even staring at it with unaided eyes is dangerous. The eye’s lens acts as a burning glass, damaging the retina. The substantially greater light and heat-collecting powers of binoculars and telescopes makes damage certain. Filters that suppress the brightness, making the observations comfortable, might not be suppressing the infrared, so you could still be damaging your sight without knowing about it. The best thing is to team up with the local astronomical society. They will know how to observe these events and will probably have an organized observing session set up. The May-June edition of “Skynews,” the Canadian astronomy magazine, contains information on the events and how and when to observe them.

On Sunday, May 20, the Moon will move between us and the Sun, causing a solar eclipse. Since the Moon will be almost at its greatest distance from the Earth, even at the centre of the shadow’s path as it sweeps across the Earth’s surface, the Moon will not cover the Sun entirely; it will leave a ring of solar disc visible. These eclipses are called annular eclipses, after annulus, the Latin word for ring. For the rest of us, we will simply see the Moon block part of the solar disc for a while — a partial eclipse. Here are the start and end times (in Local Standard Time) for a selection of Canadian cities, together with the percentage of solar disc covered. For some there is no end time because the Sun sets while the eclipse is in progress. Victoria (16:01, 18:25, 82%), Vancouver (15:59, 18:23, 80%), Penticton (16:02, 18:22, 77%), Edmonton (17:01, 19:13, 66%), Regina (18:10, 20:15, 71%) , Winnipeg (18:13, 20:11, 62%), Toronto (19:19, 29%), Ottawa (19:17, 20%), Québec (19:15 , 4%).

On June 5, the planet Venus will move between us and the Sun, and will be silhouetted against the bright solar disc.  By noting the precise timings at widely-different locations on the Earth and using triangulation, these events were used to determine the distance between the Earth and Sun. Amateur astronomers spanning Canada plan to repeat these measurements. The times below are approximate and may be out by several minutes depending upon your position. Venus will touch the edge of the solar disc around 18:09 EDT/15:09 PDT, be fully on the disc at 18:27 EDT/15:27 PDT, start to move off at 00:31 EDT (on June 6) /21:31PDT (on June 5), and it will be all over at 00:49 EDT (on June 6) and 21:49 PDT (on June 5). Those of us in the west will see more of it, and our friends in the Arctic will see it all. Again, if you plan to see either or both of these events, remember, staring at the Sun is dangerous, and looking at it through a telescope, even for a brief moment, you risk permanent irreversible damage to your sight.

Ken Tapping is an astronomer with the National Research Council's Dominion Radio Astrophysical Observatory, Penticton,  BC, V2A 6J9.

Telephone: 250-497-2300
Fax: 250-497-2355

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