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Observing the Planet Venus

If your commute takes you in a westerly direction, you may have wondered what that brilliant object in the sky was back in December. At first you might have thought it was the landing lights of a plane making its approach to Green State Airport. When it’s coming right at you it doesn’t seem to move much. After a short time of viewing you most likely realized it wasn’t approaching, though it did seem to be moving closer to the horizon.

If subsequent evenings were clear, the object was continuing to shine brightly in the same area of sky. I hope you weren’t fooled into thinking “extraterrestrial spacecraft” during your first sighting. Those later observations should have helped you to determine it was a celestial object. I’m talking about that brilliant beacon Venus.

Venus dupes more folks into alien spaceship-mode than any other planet. (Jupiter and the bright star Sirius significantly contribute to UFO sightings as well.) This confusion occurs most often when Venus is low in the sky and our atmosphere spreads the planet’s light out like a prism. It appears to shimmer, shake and even gyrate around the sky a bit. I could relate many humorous stories of people jumping to the wrong extraterrestrial conclusion.

Well, Venus is going to be visible for several months, culminating in its transit across the face of the Sun on June 5 (visible from here in Southern Rhode Island – a future Transit of Venus guide will be forthcoming as we near the date) so I thought I’d bring you up-to-date on the journey of our heavenly neighbor.

We can’t see the rocky surface of Venus since the planet is enshrouded in clouds of sulfuric acid. What do we see when we look through a telescope? All we can observe are Venus’ highly reflective clouds. And they reveal no detail to the modest telescopes of amateur astronomers. However, we can watch Venus go through phases very much like that of our Moon.

Since Venus is closer to the Sun than the Earth is, it orbits our star faster than we do. When coming around from the far side of the Sun, Venus tries to and does catch up with and passes us. Because the position angle between the Earth, Sun and Venus is constantly changing, we see Venus change phases. (Remember, one half of Venus is always illuminated, and it is our ever changing viewing angle that presents the various phases.) Please review the graphic at the following web site:
http://www.ifa.hawaii.edu/~barnes/ast110_06/rots/0520a.jpg . A picture is most definitely worth a thousand words.

Venus was on the far side of the Sun from the Earth (at superior conjunction) on August 16 of last year. Venus was then in full phase, and could we have telescopically observed it at that time from the Earth, it would have presented a small image. Once Venus moved away from the Sun’s glare could we glimpse the planet very low in the southwestern sky at sunset. That was back in early December.

Each night Venus climbed a little higher in the sky after sunset. Only then could we train our telescopes on our neighbor as it rose above the atmospheric turbulence on the western horizon. Through a telescope, Venus no longer appeared full. The planet was catching up to us each and every day, so as time went on, Venus’ image looked a little bigger as it approached the Earth, even though the illuminated portion of the planet was decreasing due to the ever changing viewing angle.

If you received a telescope over the holidays or you already had one, now is the time to put it to good use. At the beginning of February, Venus will appear 75 percent illuminated as seen from our Earthly vantage point. It will look like a waning gibbous Moon, without the craters of course. On March 27, Venus will have reached its greatest separation from the Sun and its highest elevation above the western horizon. At the same time Venus will appear like a first quarter Moon, being 54 percent illuminated. One day before this event (on the 26th), the crescent Moon will pass close to Venus. It will be a very beautiful sight. Venus will then begin its nightly descent towards the horizon and the Sun once again.

In addition, a few days later on April 3, Venus will pass in front of the Pleiades star cluster in the constellation of Taurus. Binoculars or low power on a telescope will provide the best view of this sky scene. Also, it will look its best before the sky gets completely dark.

Continue to monitor Venus as the days progress. By May 2, the planet will appear just 25 percent illuminated. The planet will also begin its plunge toward the horizon. The phase will then quickly change, from 15 percent on May 13 to only 5 percent on May 24, all the while getting larger and brighter as it approaches the Earth. At that time the planet will appear approximately four times larger in a telescope than it did way back in December because of its nearness to us. We will then quickly lose sight of Venus in bright twilight.

In less than a month Venus will then emerge in the morning sky as a thin crescent, and begin the reversal of the cycle all over again, going from crescent to last quarter to waxing gibbous to full.

However, in 2012 a special event will happen. Usually when Venus passes between the Earth and the Sun (called inferior conjunction) it passes either above or below the solar disk as seen from the Earth. On June 5, Venus will pass between the Earth and the Sun. These transits of Venus occur in pairs eight years apart. The last one was on June 8, 2004. The next one will be in 2117! During the transit, Venus will be nearest the Earth, only about 26,864,000 miles distant.

Whether you watch the progress of Venus’ 2012 western sky apparition with your unaided eye or you use binoculars or a telescope, you shouldn’t have any trouble locating this neighboring world just after sunset. Also, if you know where to scan, you can even observe Venus in broad daylight. However, it’s best to observe Venus in early twilight before the sky darkens. Venus is so bright that too much contrast is a problem when observed in a dark sky. This timing also means you will be observing the planet at its highest point off the horizon. Therefore you avoid as much atmospheric turbulence as possible.

So try to observe Venus every week or so and sketch its phase in a log book. Over time you’ll see the full range of phases our neighboring world presents. Just be thankful you happen to reside on the more temperate of the planets. At least our skies are cloud free once in a while!

Catch some great looks at Venus from any of the local observatories.

Keep your eyes to the skies.

David A. Huestis

David Huestis
Author:
David Huestis
Entry Date:
Feb 1, 2012
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David Huestis's Columns
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