Saturday, April 7, 2012

Daniel Berke and the Transit of Venus

I've let a few hints slip in some of my previous posts of a big event happening this summer, something called a “transit of Venus”. Given that as of the 5th we are only two months away from the big event, I'm going to kick off a series of posts about the subject from now till then.

First of all, you're probably wondering, what is a transit of Venus, and why is it such a big event? To start with, a transit in astronomical terms is when one object passes in front of another, and the transit of Venus is when Venus will pass in front of the face of Sun as seen from Earth.

Ok, you may be thinking, but why is it such a big deal? The answers is that transits of Venus are rare. Venus goes around the Sun in 224.65 days compared to Earth's 365.26 days, so Venus actually passes between the Earth and the Sun every 584 days, on average. If Venus actually crossed the Sun's disk every time every time this happened, they'd be about on par with total solar eclipses in rarity.

But they don't. Because of the way the orbits of Venus and Earth are aligned, Venus normally passes above or below the Sun as seen from Earth. It works out that transits of Venus only happen in pairs eight years apart, with either 105.5 or 121.5 years between pairs. The specifics of why this happens are fascinating, and something I'll go over in greater detail in a later post.

Anyway, because of their rarity, only six transits of Venus have ever been observed since the invention of the telescope over four hundred years ago: one in 1639, a pair in 1761 and 1769, a pair in 1874 and 1882, and one in 2004. But it's not just their rarity that makes them interesting. With the right measurements, a transit of Venus can be used to figure out the distance from the Earth to the Sun. Back in the 18th and 19th century, this was big news, because that distance was unknown at the time.

In fact, it was such big news that it sparked one of the first examples of international scientific collaboration on a significant scale. Dozens of expeditions were dispatched by quite a few countries to every corner of the globe in order to get as many different measurements as possible (I'll explain why it was necessary to get widely separated observations in a later post). Indeed, Captain Cook, whose third voyage made him the first European to discover Hawaiʻi, first traveled to the South Pacific (Tahiti to be specific) in charge of one such expedition.

If you've been paying attention to the numbers, you'll realize that since the last transit was in 2004, the next one won't be until 2117, so this is the last one to be seen in our lifetimes. It's also going to be visible in its entirety from Hawaiʻi, so we are expecting major crowds at the Mauna Kea Visitor Information Station where I work. While I'm excited that many people will get to see this historic event – and who knows what future great astronomers may be inspired by seeing it? – I'm also starting to feel a little overwhelmed due to the enormous number of things that need to be put in place for it to happen.

To that end I decided to put together a little humorous poster to help take my mind off all the stuff I need to get done. One of the things I'll be doing for my job in the immediate future is creating designs for a set of limited edition “Transit of Venus” T-shirts we'll be selling on The Big Day. I'm enjoying this assignment because I enjoy making astronomical art, and the stuff I've been coming up with inspired me to create this:

(Click for full size.)

I also have some prototypes of possible shirt designs done at this point in a similar vein, but I'm going to hold off on posting them till we figure out what we want to use for the official shirt. I do have some concept art for the title you can see though.


Anyway, look forward to future posts where I go over more of the fascinating science and history associated with transits of Venus. A hui hou!

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