Venus to appear in once-in-a-lifetime event

May 01, 2012
Venus. Photo courtesy of NASA

On 5 and 6 June this year, millions of people around the world will be able to see Venus pass across the face of the Sun in what will be a once-in-a-lifetime experience.

It will take about six hours to complete its transit, appearing as a small black dot on the Sun's surface, in an event that will not happen again until 2117.

In this month's , Jay M Pasachoff, an at Williams College, Massachusetts, explores the science behind Venus's transit and gives an account of its fascinating history.

Transits of Venus occur only on the very rare occasions when Venus and the Earth are in a line with the . At other times Venus passes below or above the Sun because the two orbits are at a slight angle to each other. Transits occur in pairs separated by eight years, with the gap between pairs of transits alternating between 105.5 and 121.5 years – the last transit was in 2004.

Building on the original theories of Nicolaus Copernicus from 1543, scientists were able to predict and record the transits of both Mercury and Venus in the centuries that followed.

Johannes Kepler successfully predicted that both planets would transit the Sun in 1631, part of which was verified with Mercury's transit of that year. But the first transit of Venus to actually be viewed was in 1639 – an event that had been predicted by the English astronomer Jeremiah Horrocks. He observed the transit in the village of Much Hoole in Lancashire – the only other person to see it being his correspondent, William Crabtree, in Manchester.

Later, in 1716, Edmond Halley proposed using a transit of Venus to predict the precise distance between the Earth and the Sun, known as the astronomical unit. As a result, hundreds of expeditions were sent all over the world to observe the 1761 and 1769 transits. A young James Cook took the Endeavour to the island of Tahiti, where he successfully observed the transit at a site that is still called Point Venus.

Pasachoff expects the transit to confirm his team's theory about the phenomenon called "the black-drop effect" – a strange, dark band linking Venus's silhouette with the sky outside the Sun that appears for about a minute starting just as Venus first enters the solar disk.

Pasachoff and his colleagues will concentrate on observing Venus's atmosphere as it appears when Venus is only half onto the solar disk. He also believes that observations of the transit will help astronomers who are looking for extrasolar planets orbiting stars other than the Sun.

"Doing so verifies that the techniques for studying events on and around other stars hold true in our own backyard. In other words, by looking up close at transits in our solar system, we may be able to see subtle effects that can help exoplanet hunters explain what they are seeing when they view distant suns," Pasachoff writes.

Not content with viewing this year's transit from Earth, scientists in France will be using the Hubble Space Telescope to observe the effect of Venus's transit very slightly darkening the Moon. Pasachoff and colleagues even hope to use Hubble to watch Venus passing in front of the Sun as seen from Jupiter – an event that will take place on 20 September this year – and will be using NASA's Cassini spacecraft, which is orbiting Saturn, to see a transit of Venus from Saturn on 21 December.

"We are fortunate in that we are truly living in a golden period of planetary transits and it is one of which I hope astronomers can take full advantage," he writes.

Explore further: Image: Kaleidoscopic view of Mars

add to favorites email to friend print save as pdf

Related Stories

Rare transit of Mercury

Nov 02, 2006

Scientists from Williams College and the University of Arizona observed Mercury in front of Venus from vantage points on earthbound mountains and with orbiting spacecraft on Wednesday.

The mystery of Venus’ ashen light

Apr 30, 2012

May is the best time to try and spot one of the most enduring unsolved mysteries in our Solar System. Ashen Light is a faint glow allegedly seen on the unlit portion of Venus, during its crescent phase, similar to the earthshine ...

Venus Express spacecraft fires main engine

Feb 20, 2006

One hundred days after its launch to Venus, the European Space Agency's Venus Express has successfully tested its main engine for the first time in space.

Recommended for you

New launch date set for ISS delivery vessel

8 hours ago

A robot ship will be launched from Kourou, French Guiana, after a five-day delay on July 29 to deliver provisions to the International Space Station, space transport firm Arianespace said Tuesday.

The heart of an astronaut, five years on

10 hours ago

The heart of an astronaut is a much-studied thing. Scientists have analyzed its blood flow, rhythms, atrophy and, through journal studies, even matters of the heart. But for the first time, researchers are ...

Image: Kaleidoscopic view of Mars

16 hours ago

Astrophotographer Leo Aerts from Belgium took advantage of the recent opposition of Mars and captured the Red Planet both "coming and going" in this montage of images taken from October 2013 to June of 2014. ...

User comments : 8

Adjust slider to filter visible comments by rank

Display comments: newest first

Infinite Fractal Consciousness
3 / 5 (2) May 01, 2012
"Pasachoff and colleagues even hope to use Hubble to watch Venus passing in front of the Sun as seen from Jupiter..."

Does this make any sense? typo?
Onathan
1 / 5 (1) May 01, 2012
"Pasachoff and colleagues even hope to use Hubble to watch Venus passing in front of the Sun as seen from Jupiter..."

Does this make any sense? typo?


In the context of the previous sentence - "using the Hubble Space Telescope to observe the effect of Venus's transit very slightly darkening the Moon" - presumably they hope to see a dimming of Jupiter.

What really doesn't make sense is the "once-in-a-lifetime" headline, when the third paragraph points out that transits come in "pairs separated by eight years ... the last transit was in 2004."
kaasinees
0.6 / 5 (29) May 01, 2012
Its popping out to show us how bad earth will be when we output too much CO2.
daqman
5 / 5 (2) May 01, 2012
Now I know which days are going to be cloudy. It's much more reliable than a weather forecast.

Spectacular astronomical event = dense cloud here.
Lurker2358
not rated yet May 01, 2012
What really doesn't make sense is the "once-in-a-lifetime" headline, when the third paragraph points out that transits come in "pairs separated by eight years ... the last transit was in 2004."


If you were born in 2005, or even the day after the first transit in the pair, it is highly unlikely that you will live to see the first transit in the next pair, although some few centenarians approaching the official records might be lucky enough to live that long.
Infinite Fractal Consciousness
1 / 5 (1) May 01, 2012
For everyone older than 7, it's a twice-in-a-lifetime event.
Lurker2358
5 / 5 (2) May 01, 2012
For everyone older than 7, it's a twice-in-a-lifetime event.


Actually, my dad didn't see any of them guy, died before either of them.

Don't be so quick to draw conclusions.
Anda
1 / 5 (1) May 01, 2012
"Pasachoff and colleagues even hope to use Hubble to watch Venus passing in front of the Sun as seen from Jupiter..."

Does this make any sense? typo?


Yes... Find it