Transit of Venus
On June 8, 2004, a transit of Venus will occur, the first in 122 years. This article explains what a transit is, why it matters, and when and how you can safely view it.
A photograph of the 1882 transit of Venus, the last seen from Earth (More about the photograph)
A larger image is available.
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Related pages
- Astronomy: Spark students' interest in outer space with this collection of great astronomy websites found in LEARN NC's Best of the Web.
- Natural Science Center of Greensboro: Features hands-on exhibits, a zoo, and a planetarium as well as a dinosaur exhibit and a Gem and Mineral Gallery.
- Robeson Planetarium/Science and Technology Center: A part of the public schools of Robeson County, this planetarium and science center specializes in programs geared to 3rd through 8th grade science.
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On June 8, 2004, Venus will pass in front of the Sun as seen from earth. No one now alive has ever seen this happen. If you have any interest in astronomy, this is not to be missed! This article will explain what the transit of Venus is, why it matters, and when and how you can safely view the one coming up in June.
Planetary transits
A transit of Venus occurs when the planet Venus moves directly between the Earth and the Sun. It’s like a solar eclipse, except that Venus appears so small from Earth that it doesn’t block out the Sun’s disc as the moon does. From Earth, it will appear as a small black dot moving across the Sun’s face.
Transits of planets across the Sun are very rare. Transits of Mercury occur about thirteen times in a century. Transits of Venus typically come in pairs, eight years apart, with pairs of transits separated by more than a century. The last pair of transits occurred in 1874 and 1882, and the next transit after this year’s will happen in 2012. After that, you’ll have to wait until 2117 to see another one — assuming medicine advances to the point where we live that long!
Because only Venus and Mercury pass between the Earth and Sun, only those planets have transits — at least as seen from Earth. If you were on Mars at the right time, you could see a transit of Earth.
Why do transits matter?
Historically, transits of Venus provided important information to astronomers about the distance between the Earth and Sun. By stationing observers at various points on the Earth’s surface and precisely timing the planet’s appearance on the Sun’s disc, astronomers could use trigonometry to calculate the absolute distances between the three bodies.
To do this, astronomers used what is called the parallax of the Sun. This definition from the National Solar Observatory explains:
Parallax is the effect that nearby objects seem to move relative to far-away objects when you move to another viewpoint. For instance, if you hold your finger in front of your nose and look at it with just one eye at a time (without moving your finger), then you’ll notice that your finger blocks different parts of the background depending on which eye looks at it.
Want a more detailed mathematical explanation? Sounds like a project for your trigonometry class! We’re not going to do all the work for you! Today, we can measure distances within the solar system with radar, so the 2004 transit isn’t as important as the ones in the eighteenth and nineteenth centuries. But a planetary transit is still a really cool thing to see.
When and where to see it
The times of the Venus transit as seen in various cities in North Carolina are provided by NASA. Note that the times are given in UT — that’s Universal Time, or standard time at the Greenwich Meridian that runs through Greenwich, England. To find times for EDT, subtract four hours from UT.
The four contact times listed on the chart define the planet’s ingress (entering the sun) and egress (leaving the sun): Contact I is the point at which Venus first appears to touch the sun’s disc from the outside; Contact II is the moment when it is completely inside the sun’s disc; Contact III is the moment when it touches the sun’s disc from the inside on the way out; and Contact IV is the moment when it disappears outside the sun.
In North Carolina, Venus will already be in transit when the sun rises on June 8, so the transit will be visible from sunrise (about 6 a.m.) until 7:26 a.m. So you’ll have to get up early to see it.
How to see it — safely
Now this is important, so pay attention. Don’t look directly at the sun. Never ever not ever. You’ve been told before. You’ve probably told other people. Just a few seconds of direct sunlight will permanently damage your retina, quite possibly causing blindness — and do it painlessly, so you’ll never know it’s happening until the damage is done.
To view the transit of Venus, you’ll need to use filters, mirror projection, or a pinhole camera. (A pinhole camera might produce too small an image for you to see Venus clearly, though.) This page from England gives guidelines on safely viewing a solar eclipse, and they apply to the transit as well. If you want to use viewing filters, make sure they are from a reputable source. They’re available in bulk from sources recommended by NASA.
