Solar Dynamics Observatory to observe Venus transit

Jun 01, 2012
Venus appears as a black dot on the lower left edge of the sun in this image from NASA's Transition Region and Coronal Explorer (TRACE), captured during the 2004 transit. Credit: NASA/TRACE/LMSAL

On June 5, 2012 at 6:03 PM EDT, the planet Venus will do something it has done only seven times since the invention of the telescope: cross in front of the sun. This transit is among the rarest of planetary alignments and it has an odd cycle. Two such Venus transits always occur within eight years of each other and then there is a break of either 105 or 121 years before it happens again.

The moments when Venus first appears to cross the limb of the sun and the moments it leaves, known as ingress and egress respectively, are historically the most scientifically important aspects of the transit since comparison of Venus's journey viewed from different points on Earth provided one of the earliest ways to determine the distance between Earth and the sun. The transit is also helpful to scientists today: NASA's Solar Dynamics (SDO) will be watching the June 2012 transit to help calibrate its instruments as well as to learn more about Venus's .

Since the points at which Venus will first touch and later leave the sun is known down to minute detail, SDO can use this information to make sure its images are oriented to true solar North. Orienting instruments is a constant adjustment game for telescopes in space, since their original position can be shifted during launch. Various calibrations throughout the two years SDO has been in space have left the scientists confident that the instruments are highly accurate, but making sure that Venus appears in the SDO images exactly where scientists know it should be will help make sure SDO's is accurate to within a tenth of a pixel.

Second, the SDO team can use the lightless center of Venus to help calibrate what is called the point spread function of the . This function describes how much light leaks from one pixel into others around it. Since there is no light emitted from the very center of Venus as it crosses the sun, it serves as a perfect test case for an area of the image where the pixels should remain black. By measuring how much light bleeds into those pixels from the rest of the sun, the SDO team will have a better sense of how to correct for that. These measurements also help us to understand the black drop effect – in which a tiny black spot appears to connect Venus to the limb of the -- that bedeviled scientists' attempts to measure the exact position of Venus during transits in the 18th and 19th centuries.

And last, the SDO team hopes to learn more about Venus's atmosphere as it is partially transparent to the extreme ultraviolet light observed by the telescopes on . Venus will appear to be a little bigger in longer wavelengths (such as 304) as compared to shorter wavelengths (such as 171). This difference tells us how much oxygen is in Venus's atmosphere.

Explore further: France raises heat on decision for next Ariane rocket

add to favorites email to friend print save as pdf

Related Stories

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

May 01, 2012

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.

Get ready for the transit of Venus

May 25, 2012

Scientists and amateur astronomers around the world are preparing to observe the rare occurrence of Venus crossing the face of the Sun on 5-6 June, an event that will not be seen again for over a hundred years.

ND expert: The science behind the transit of Venus

May 30, 2012

University of Notre Dame professor of physics Peter Garnavich has research interests that cover a wide range of topics in observational astrophysics. In preparation for the Tuesday (June 5) Transit of Venus, he offers an ...

The 2012 transit of Venus

May 18, 2012

On June 5th, 2012, Venus will pass across the face of the sun, producing a silhouette that no one alive today will likely see again.

Solar Dynamics Observatory goes for a spin

Apr 09, 2012

(Phys.org) -- On April 4, 2012, NASA's Solar Dynamics Observatory (SDO) did a 360. It rolled completely around its axis – something it does twice a year. In this movie, the dizzying view looks as if the ...

Recommended for you

Miranda: An icy moon deformed by tidal heating

12 hours ago

Miranda, a small, icy moon of Uranus, is one of the most visually striking and enigmatic bodies in the solar system. Despite its relatively small size, Miranda appears to have experienced an episode of intense ...

The latest observations of interstellar particles

18 hours ago

With all the news about Voyager 1 leaving the heliosphere and entering interstellar space you might think that the probe is the first spacecraft to detect interstellar particles. That isn't entirely true, ...

User comments : 0