VENUS TRANSIT
JUNE 5/6, 2012
On June 5/6 2012 Venus crossed the Sun's disk, producing an extremely rare Venus Transit. Venus could be seen in silhouet as a large black spot.
Astronet and 'Planetary Paul' were organising a live webcast of the Venus transit from The Netherlands. Unfortunately, Planetary Paul was clouded out completely.
But luckily there were many other stations around the world and from outer space that provided webcasts and live streamings of the event.
Images from outer space taken by NASA's Solar Dynamics Observatory (SDO).
LIVE WEBCASTS
Excellent images were brought by Slooh Space Camera
The Transit of Venus was succesfully webcasted by astro.viten.no.
NASA's did live streaming from the top of Mauna Kea, Hawaii.
Unfortunately Planetary Paul,
Haarlem, The Netherlands. was completey clouded out.
OTHER LIVE WEBCASTS:
- Sky Watcher's Association of North Bengal (SWAN), India.
- Astronomers Without Borders, Mount Wilson Observatory, California, USA
- Bareket Observatory, Israel
- W.M. Keck Observatory, Mauna Kea, Hawaii
- Slooh Space Camera, USA
- National Solar Observatory, USA
- Astro Viten, Noorwegen
- Exploratorium, Mauna Loa Observatory, Hawaii
- Columbus State University’s Coca-Cola Space Science Center (CCSSC), USA, Australia, Mongolia
- Transit of Venus 2012, Australië
- Planethunters.org, GLORIA project, Tromsø in Norway, Sapporo in Japan en Carins in Australië
- Physics and Astronomy AstroCam, Appalachian State University, North Carolina, USA
- Departement d'Astronomia i Meteorologia, Universitat de Barcelona-ICC/IEEC, broadcast vanaf Svalbard
- Mount Lemon Sky Center, Arizona, USA
- Horowhenua Astronomical Society, New Zealand
- Arthur C. Clarke Institute, Sri Lanka
- University of North Dakota, broadcasting from Alaska, USA
- Kwasan Observaotry, Kyoto, Japan
- Amateur Astronomers Association Delhi, Ladakh, Himalayas
- Vigyan Prasar Science Portal, Himalayan Chandra Telescope, Hanle
The Venus transit could also be followed on the H-alpha images that
are continuously broadcasted by the NSO/GONG H Alpha Network Monitor of solar telscopes around the Earth.
Astronomy Picture of the Day, in cooperation with NASA/SDO provided very detailed solar images.
YouTube: The Venus Transit was observed and photographed from the International Space Station (ISS)
Don Pettit, flight engineer on board of the International Space Station (ISS), will photograph the Venus Transit from one of the windows of the cupola
of ISS. Pettit's pictures will be posted at this Photostream.
Find local activities worldwide.
THE TRANSIT
Transits of Venus across the disk of the Sun are among the rarest of planetary
alignments. Only seven such events have occurred since the invention of the
telescope (1631, 1639, 1761, 1769, 1874, 1882 and 2004). Transits of Venus are only
possible during early December and early June when Venus's orbital nodes pass
across the Sun. If Venus reaches inferior conjunction at this time, a transit will occur.
Transits show a clear pattern of recurrence at intervals of 8, 121.5, 8 and 105.5 years.
This transit is the last one of the part of the pair 2004 June 8 and 2012 June 5/6.
The next pair of Venus transits occur over a century from now on 2117 Dec 11 and
2125 Dec 08.
Animation of the Venus Transit, by Marc van der Sluys of Dutch website hemel.waarnemen.com.
The principal events occurring during a transit are characterized by contacts.
The event begins with contact I which is the instant when the planet's disk is
externally tangent with the Sun. The entire disk of the Venus is first seen at
contact II when the planet is internally tangent with the Sun. During the next
several hours, Venus gradually traverses the solar disk at a relative angular
rate of approximately 4 arc-min/hr. At contact III, the planet reaches the opposite
limb and is once again internally tangent with the Sun. The transit ends at
contact IV when the planet's limb is externally tangent to the Sun. Contacts
I and II define the phase called ingress while contacts III and IV are known as
egress. Greatest transit is the instant of minimum angular separation between Venus
and the Sun as seen from Earth's geocenter. Position angles for Venus at each contact
are measured counterclockwise from the north point on the
Sun's disk.
The Venus Transit. Courtesy: Fred Espenak
As can also be seen in above's diagram, the geocentric phases are:
| Event | Universal Time | Position Angle |
| | | |
| Contact I | 22:09:38 | 41o |
| Contact II | 22:27:34 | 38o |
| Greatest | 01:29:36 | 345o |
| Contact III | 04:31:39 | 293o |
| Contact IV | 04:49:35 | 290o |
These geocentric times are for an observer at Earth's center. The actual contact times for any given observer may
differ by up to ±7 minutes. This is due to effects of parallax, since Venus's 58 arc-second diameter disk may be
shifted up to 30 arc-seconds from its geocentric coordinates depending on the observer's exact position on Earth.
Here is a list of predicted contact times and corresponding altitudes for a number of cities around the world.
Here are lists of similar predictions for locations throughout
Canada and the USA.
The entire transit (all four contacts) is visible from northwestern North America, Hawaii, the western Pacific,
northern Asia, Japan, Korea, eastern China, Philippines, eastern Australia, and New Zealand.
The Sun sets while the transit is still in progress from most of North America, the Caribbean,
and northwest South America. Similarly, the transit is already in progress at sunrise for observers
in central Asia, the Middle East, Europe, and eastern Africa,. No portion of the transit will be
visible from Portugal or southern Spain, western Africa, and the southeastern 2/3 of South America.
(Note that due to the International Date Line the Western Hemisphere will see the transit on June 5.)
The visibility of the Venus Transit. Courtesy: Fred Espenak/NASA
SAFETY
The apparent semi-diameters of Venus and the Sun are 29 arc-seconds and 945
arc-seconds respectively. This 1:32.6 diameter ratio results in an effective
0.001 magnitude drop in the Sun's integrated magnitude due to the transit.
This simply means that the Sun will be as dangerous for our eyesight at the
time of the Venus Transit as it is on any normal day, when there is no planet
in front of the solar disc.
NEVER LOOK DIRECTLY AT THE SUN WITH UNPROTECTED EYES - THIS MAY CAUSE TOTAL
BLINDNESS WITHIN SECONDS! ALWAYS BE SURE TO USE PROPER OPTICAL FILTERS TO
PROTECT YOUR EYES.
The use of #14 shade welding glass or eclipse shades will permit a large number
of people who do not have specialized equipment to observe this event.
However, as the planet approaches the limb of the Sun, subtleties like the
black drop effect may not be discernible. Pinhole projectors are a safe,
indirect viewing technique for observing an image of the Sun. While popular
for viewing solar eclipses, pinhole projectors suffer from the same
shortcomings as unmagnified views when Venus approaches the edges of the Sun.
Small features like the black drop effect and the halo around Venus while it
straddles the solar edge may not be discernible.
You may project a magnified view of the Sun through a telescope onto a surface,
but the technique often has its own limitations. For example, large reflector
telescopes can generate too much heat by concentrating a lot of the Sun's energy
on the secondary mirror and eyepiece. Likewise, Schmidt-Cassegrain telescopes
can experience too much heat build-up as the light bounces internally. Also,
magnified projections usually have an exposed focal point beyond the eyepiece
where bystanders could inadvertently burn themselves. Constant attention is
required.
Projecting a magnified view of the sun through a telescope on a surface. Illustration and photograph: European Southern Observatory.
The transit of Venus is perhaps best viewed directly when magnified, which
demands an appropriate solar filter over the large end of the telescope.
Do not use small filters that fit over the eyepiece, for the concentrated
sunlight can shatter them. The sun's energy must be attenuated before
it enters the telescope. A filtered, magnified view will show the planet Venus,
the "black drop" effect, and sunspots.
No matter what technique you use for viewing the sun, do not stare continuously
at the sun! Always give your eyes a break.
MEASURING THE SOLAR SYSTEM
In earlier times, astronomers used transits of Mercury and Venus to get information
about the dimensions of the solar system: the size of the Sun, the distance of Venus,
and the distance between us and the Sun, which is called the astronomical unit (AU).
To fix that important quantity, astronomers used the method of triangulation.
Aside from its rarity, the original scientific interest in observing a transit of Venus was that it could be used to determine the distance from the Earth to the Sun, and from this the size of the Solar System,
by employing the parallax method and Kepler's third law. The technique involved making precise observations of the slight difference in the time of either the start or the end of the transit from widely separated points
on the Earth's surface. The distance between the points on the Earth was then used as a baseline to calculate the distance to Venus and the Sun via triangulation. Illustration: Vermeer/Wikipedia.
The first astronomer to recognize the importance of observing transits of Mercury
and Venus was Edmund Halley (1656-1742). It appeared to the observer, using a
telescope as the lens of a camera obscura (never look directly at the Sun through
a telescope!) as a black dot crossing the surface of the Sun. The first astronomers
to use telescopes to observe the transit of Venus were Jeremiah Horrocks (1618-41)
and William Crabtree (1610-44) in 1639.
Astronomers travelled to remote parts of the world to observe the transits of Venus
in 1761 and 1769. To observe the transit of 1769, Captain Cook sailed from England
to Tahiti. He discovered Hawaii and a few other places as bonuses along the way;
it is not often that the side benefits of astronomical research are so apparent.
How accurate were the measurements of Cook? The "dusky shade round the body of the
Planet" as he descrtibed the appearance of Venus was a problem. Intense sunlight
filtering through Venus' atmosphere fuzzed the edge of the disk and decreased the
precision with which Cook could time the transit. For this reason, his
measurements disagreed with those of ship's astronomer Charles Green, who
observed the transit beside Cook, by as much as 42 seconds.
Cook and Green also observed the "black drop effect." When Venus is near the
limb of the sun--the critical moment for transit timing--the black of space
beyond the Sun's limb seems to reach in and touch the planet. You can recreate
the black drop effect with your thumb and index finger: Hold the two in front
of one eye and narrow the distance between them. Just before they touch,
a shadowy bridge will spring across the gap. According to John Westfall,
writing for Sky & Telescope magazine in June 2004, "this is simply the result
of how two fuzzy bright-to-dark gradients add together." The black drop effect,
like the fuzziness of Venus' atmosphere, made it hard to say just when the transit
began or ended.
Black drop effect
This was a problem for observers elsewhere, too, not only Cook in Tahiti. In fact,
when all was said and done, observations of Venus' 1769 transit from 76 points
around the globe, including Cook's, were not precise enough to set the scale of
the solar system. Astronomers didn't manage that until the 19th century when they
used photography to record the next pair of transits. And even then an incertainty
in the measurements remained.
In recent years, radio signals emitted by spacecraft as they pass behind Venus
have enabled us to obtain very accurate planetary positions and masses, as well
as the distance between the Earth and the Sun. Because of these results from space
exploration, observing this and future planetary transits will be of less scientific
importance, but they will of course continue to be great public and educational
interest.
JOIN THE OBSERVATIONS!
Join the project of Prof. Dr. Udo Backhaus of Universität Duisburg in Essen!
He will calculate the distance from the Earth to the Sun using your contact timings .
He will also use photographic images taken from different places on Earth
to do the calculations.
Dutch physicist Steven van Roode developed a special and free Phone App
to report contact timings for a similar calculation.
Transit of Venus 2012 of the Bradford Robotic Telescope Project has an automatic algorithm
for reporting contact timings. The results can be checked online.
Astronet.nl welcomes your photographs! Send your best pictures (3 at most, maximum size 1200 x 900 pixels) to:
What else is there to be seen? Look before and during ingress and during and after
egress for a spectacular 'light ring' around the black silhoutte of Venus. This
is caused by sunlight that is refracted by Venus' thick atmosphere. It was after
observing this light ring in 1761 that Russian astronomer Mikhail Lomonósov
realized that Venus is surrounded by an atmosphere.
The light ring in 1874
During the recent Venus Transit of 2004, June 8, the light ring around Venus could be clearly seen.
RESEARCH
The 2012 transit will give scientists a number of research opportunities. Astronomers can measure of dips in a star's brightness caused by a known planet transiting a known star (the Sun).
This will help astronomers when searching for exoplanets. Unlike the 2004 Venus transit, the 2012 transit occurs during an active phase of the 11-year activity cycle of the Sun, and is likely to provide
practice in detecting a planet's signal around a "spotty" variable star.
The atmosphere of Venus can be observed simultaneously from Earth-based telescopes and from the Venus Express spacecraft. This will give a better opportunity to understand the intermediate level
of Venus's atmosphere than is possible from either viewpoint alone, and will provide new information about the climatology of the planet.
The atmosphere of Venus can be studied using a spectrograph. The results of analysis of the well-understood atmosphere of Venus will be compared with studies of exoplanets with atmospheres that are unknown.
The Hubble Space Telescope cannot look at the Sun directly. But Hubble will be aimed at lunar crater Tycho and study the reflected sunlight to detect spectral fingerprints of Venus' atmosphere. This may provide another technique to study exoplanets.
Carl Koppeschaar
FURTHER INFORMATION
General information:
History of Venus Transits:
The Black Drop Effect
Topocentric contact times and corresponding altitudes of the Sun:
Past and future Venus Transits:
Safety:
Time synchronization:
Solar Parallax Calculation:
Research:
Trivia:
As a result of posting this webpage on Wikipedia's Venus Transit web pages, my IP address was blocked by a certain "Melos" (Wikipedia administrator). This webpage
and its Dutch language mirror took me many unpaid hours to compose. As anyone can see it contains no advertisments or hidden scripts
whatsoever. I am an astronomer and a science journalist. I only want to inform the public, as I did many times before with live webcasts of solar and lunar eclipses, Mercury transits and the 2004
Venus transit.
Wikipedia should first investigate before they block a serious contribution! German poet, philosopher, historian and playwright Friedrich Schiller (Johann Christoph Friedrich von Schiller, 1759 - 1805) knew it:
"Mit der Dummheit kämpfen Götter selbst vergebens." (Talbot in Die Jungfrau von Orléans, III, 6)
In plain English:
"Against stupidity, the gods themselves contend in vain."
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