Soon the trifecta will be complete. Originally a horse racing term, but now often used to refer to three important things coming together at the same time, tomorrow’s transit of Venus will be the third in a series of celestial alignments that included the May 20 annular eclipse of the sun and this morning’s partial lunar eclipse.
Although I got up at 4:45 a.m. with hopes of seeing the moon touched by Earth’s shadow, clouds eclipsed the entire sky. I hope some of you were more fortunate. The weather looks good in my neighborhood for tomorrow’s (June 5) Venus transit, which across North America begins within a couple minutes of 22:05 Universal time or 6:05 Eastern Daylight, 5:05 p.m. Central, 4:05 p.m. Mountain and 3:05 Pacific time.
In Duluth, Minn. we should see the first sign of Venus’ silhouetted self touch the northeastern limb of the sun at 5:04 p.m. This moment is called first contact. 18 minutes later the opposite side of the planet will touch the inner limb of the sun at second contact. A little more than 6 hours later Venus will again touch the inner limb on the western side of the sun during third contact before slowly exiting the sun’s disk (fourth contact). While you may applaud at transit end, don’t expect an encore until the year 2117.
By now, you’ve probably planned out how you’re going to view the event. Methods include special mylar or glass filters coated to reduce the sun’s light UV and infrared light to a safe level. You can also use a #14 welders glass, pinhole projection using a cardboard box or project the sun’s image onto white poster board with binoculars. If you plan on projecting the sun’s image and still need help on how, click HERE for an excellent guide.
It’s important to set up at least a half hour before the transit begins, so you don’t miss the first 20 minutes and /or the last 20 minutes, arguably the most exciting times for viewing. Here are things to watch for:
* Aureole of Venus’ atmosphere — This is a faint, extremely narrow annulus or ring of light visible around the planet at first contact through a telescope. Use as high a magnification as possible without blurring the image. As Venus moves farther into the sun, the ring will shrink to a arc and then disappear.
What you’re seeing is Venus’ thick atmosphere backlit by the brilliant sun. The air on Venus is mostly carbon dioxide and about 100 times as dense as Earth’s. Lower down, clouds of sulfuric acid sprinkle the red-hot, 800-degree surface with a particularly nasty version of acid rain. The sequence of events are reversed during third and fourth contacts.
Venus’ ring is very similar to the ring of light around the Earth that an astronaut on the moon would see when we on Earth experience a total lunar eclipse. Picture the astronaut watching the big silhouetted Earth cover the sun, its circumference aglow with the oranges and reds of low-angled sunlight. That very same light, bent by the atmosphere into Earth’s shadow, colors the moon during eclipse.
* Black drop effect — I described this in an earlier blog, but let’s have one more go at it. As the last bit of Venus moves into the sun’s disk at second contact, you might see the planet momentarily shaped like a teardrop. The side of Venus’ disk closest to the sun’s inner limb will appear to stretch toward it momentarily as a black ligament before “snapping” free.
You can see a similar effect by holding out a hand against a smooth, light backdrop and barely touching thumb and index finger. It’s caused by a combination of blurring from turbulence in Earth’s atmosphere and the natural darkening along the sun’s inner edge.
* Blackness of planet vs. sunspots — Venus will easily win out for being blacker than the darkest sunspots. As of this morning there are seven sunspot groups out, so it’ll be easy to compare.
* Happy alignment — Expand your mind and picture the whole scene as you’d see it far above the Earth in outer space with the sun, Venus and Earth, Venus all sitting pretty in a row.
If it’s cloudy at your place tomorrow, you can always watch the live NASA webcast. Locally here in Duluth, the Marshall W. Alworth Planetarium on the UMD campus will have people and telescopes on hand for anyone wanting to come by for a look starting at 5 p.m.
Tomorrow we’ll look at what scientists hope to learn from the transit.