Venus Transit

English: Venus atmosphere illumanted by cross ...

English: Venus atmosphere illumanted by cross sun transit (Photo credit: Wikipedia)

I would be negligent in the extreme if I didn’t spend time talking about this key event.

Tomorrow, the planet Venus will pass between Earth and the sun.  That means that we can see it silhouetted against the sunlight.

Why is that so cool?  I’ll give you a list…

1- Because the orbital planes of Venus and Earth are not precisely the same, these transits occur only twice every 100something years…8 years apart.  This will be the second one this go round, so it won’t happen again in your lifetime.

2- For reasons I don’t understand well enough to explain, this event has been used to measure the precise distance between the Earth and the Sun.  It has to do with the exact time that Venus enters and leaves the Sun‘s disk.   We actually have better ways to do that these days, but it is still fun to think about. Historically, astronomers have traveled great distances, sometimes with significant personal risk, to view occurrences of this event and collect science from them.

3- For some parts of the world, I’m told that Venus won’t travel straight across the sun’s disk, but will seem to pull a kind of loop-de-loop as it passes us in space.  I’m not sure if this is true, but if it is then Hawaii is a great place to observe it and NASA will have a webcam setup there to view the transit.

4- As the event begins, when Venus first has the Sun behind part of it, astronomers can determine the exact composition of Venus’ atmosphere as sunlight passes through it.

5- Because we already have a pretty good understanding of the size, orbit, and atmosphere of Venus, scientists will use this transit to test equipment used to measure these things on planets orbiting other stars as they transit.

Now please, please, please, please don’t look directly at the sun without a filter (#14 welding mask glass or equivalent).  To do otherwise will blind you.  Sunlight passing through the lens of your eye does the same thing to your retina that sunlight passing through a magnifying glass does to ants. Ordinary sunglasses are designed to protect you from reflected sunlight, but they are not enough for staring directly at the sun, so don’t attempt it for any amount of time.  Our sun can be seen from a thousand light years away…it’s very bright.  You might also consider projecting the sunlight through a pinhole camera, or a pair of binoculars.

Venus is very small and far away, so for the best view of the transit you should use a telescope.  Again, it will need a proper filter designed for your specific equipment.  See your telescope’s manufacture for the right stuff. 

For most of us, a better experience might be had online.  Many observatories all over the world will point their instruments at this event…equipment that you and I can’t afford to set up in our back yard…and some will transmit their view via the Internet.  They’ll zoom in tight so you can see Venus all big and clear and they’ll use special filters installed to improve the experience.  Even afterwards, even if you view the event without the Internet, you’ll want to check out images made from the Hubble Space Telescope and other observatories.

There are a ton of great details into what I’ve said here at

Have fun viewing this historic transit, but above all please be careful with your eyes.  There will be lots more great, special, once-in-a-lifetime things in your future that you won’t want to miss seeing.

Clear Skys!

Update: Check this out. A cheap telescope with the eyepiece projecting onto a ghost board. I had to find a spot in my yard mostly out of the wind because there’s a storm coming. But I can see Venus clearly in between passing clouds.

~ by Bill Housley on June 4, 2012.

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