Transit of Venus – June 5th – and why it matters

Seth Jarvis

A Transit of Venus…

A tiny black dot taking hours to cover a distance no greater than the width of a pea held at arm’s length.

A rare alignment of Earth, Venus and the Sun, resulting in Venus appearing to move slowly across the face of the Sun…



What’s all the fuss about?  Why should you care?

1)     Because a Transit of Venus is a scientifically important event.  Measuring the precise time of Venus first making contact with the visible edge of the Sun, and the precise time of Venus making its last contact with the Sun, from widely separated locations across the Earth, enabled astronomers to obtain the first reasonably accurate estimates of the size of our solar system.

Prior to the first measured Venus transit, all we knew about the distances between planets and the Sun were their relative scale distances, not their absolute distances in miles or kilometers.  Sure, we knew that Jupiter is about five times farther from the Sun than Earth, but what’s the absolute value in miles or kilometers of the Earth-Sun distance?  Accurately measuring the Transit of Venus first allowed astronomers to calculate this distance.

And even though today we know with great precision the average Earth-Sun distance, observing the Transit of Venus on June 5th allows astronomers to calibrate their methods for determining how the passage of an Earth-sized world in front of a Sun-like star causes the star’s light to dim. This provides astronomers a way to test and refine their methods for searching for Earth-like planets orbiting stars elsewhere in our galaxy.

A Transit of Venus also allows astronomers to measure the way that Venus’ thick atmosphere filters sunlight as it passes in front of the Sun. This provides invaluable information to astronomers who want to learn about how it might be possible to detect and study the atmospheres of planets orbiting stars elsewhere in our galaxy.


2)     Because a Transit of Venus is an historically important event. The efforts that were undertaken to first use a Venus Transit as a means to measure the size of our solar system produced the first international and intercontinental cooperation by scientists towards achieving a common goal. No longer was scientific research carried out by individual scientists working independently of one another. To measure the solar system it would be necessary for multiple teams of astronomers to cooperate and coordinate globally to observe and measure the transits of Venus in 1761 and 1769.  They made plans for this international, intercontinental, highly complicated undertaking while in the middle of the Seven Years’ War.  It was no small thing to accomplish.  International scientific efforts to observe the transits of Venus in 1761 and 1769 have been referred to as “the Apollo program of the 18th Century.”


3)     Because Transits of Venus are very, VERY rare. A Transit of Venus occurs only when the Sun, Venus and Earth align in a very particular way. Generally speaking, Transits of Venus occur in pairs, each half of the pair being about eight years apart, and with a gap of approximately 120 years between pairs.  Get that?  More than a century.

The June 5th 2012 Transit of Venus is the second half of the pair, the first being a Venus Transit in 2004 that was not visible in the western hemisphere.

The last pair of transits was 1872 and 1882.  The next pair of transits will be the years 2117 and 2125.  Only the transit in 2125 will be visible from Utah.  (Kind of interesting to think about what Utah will look like in 2125, don’t you think?)

The transit begins at about 4:00 PM on Tuesday, June 5th and lasts until sunset a little before 9:00 PM.

If you miss seeing this Transit of Venus, you’ve either got to:

a)     Plan to be alive for another 113 years, or,

b)     Resign yourself to the fact that you were given a chance to see a once-in-a-lifetime wonder of nature of major scientific and historical importance… and you blew it off.


Facts to remember:

Yes, we have a fresh shipment of solar viewing glasses arriving next week (~May 30th) in time for the June 5 transit.  The solar viewing glasses we’ll get next week will be Aluminized Mylar filters, which will provide clear, color-free views of the transit. Venus will appear as a tiny black dot moving slowly across the face of the Sun.

Yes, the solar viewing glasses you bought for the May 20th eclipse will work just fine for the transit.  If you’ve got solar viewers from the May 20th eclipse, use them!

No, the pinhole projectors you made for the May 20th eclipse will not allow you to see Venus.  The image of the Sun in a pinhole projection box won’t be big enough or of sufficient resolution to show Venus against the Sun.

YES, Clark Planetarium staff and local amateur astronomers will again have solar telescopes set up both here at the Gateway Mall (by the Olympic fountain), and at the Dimple Dell Recreation Center at 106th South and 10th East in Sandy for free public viewing of the transit.

Look, Captain James Cook spent three years at sea just getting to Tahiti and back in order to observe a Transit of Venus, but all you’ve got to do is show up at one of our free Venus Transit viewing sites.

Come!  See something cool, learn about Venus, and experience something fascinating to tell your great-grand kids about. You won’t regret it.

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