Of course we all know the Transit of Venus is occurring tomorrow. This is huge, check out my last post to see why.
I just got off the radio show I co-host (It’s called YorkUniverse, airs mondays at 9pm local Toronto time over www.astronomy.fm), and we were chatting about how the size of Venus has changed over the last couple months. The amazing astrophotographer Ian Uhlir (along with Ted Rudyk, Cissy Suen, Bryce Petersen) provided a great collage of the planet Venus changing in apparent size since February of this year.
So a transit occurs when the planet Venus passes in between us (the Earth) and the Sun. But in the months leading up to that, the planet Venus is orbitally ‘catching up’ to us. Remember that Venus’ orbit is smaller than Earth’s, it goes around the sun in 225 days (we take 365 days, roughly). As a result, sometimes Venus is far from us (when it is on the opposite side of the Sun, for instance) and sometimes it is close to us (as it heads towards inferior conjunction, or a transit in this case). The above collage was generated by taking images of Venus using the EXACT same telescope set up over a period of a few months. This means, the images are all scaled properly and the difference in size between images of Venus is not an artifact of the method by which Venus was imaged, but reflects the fact that Venus actually appears LARGER to us, because it is PHYSICALLY closer.
Unbelievably cool to see this collage, and to see how noticeably different in size the planet Venus is at different parts of its orbit. As a matter of interest, Venus is 110 miilion kilometers from the Sun, we’re 150 million. But when Venus is on the other side of the Sun, it can be as much as 260 million kilometers away fom us, and when it’s at inferior conjunction it can be as little as 40 million kilometers away from us. It makes sense Venus’ relative size changes so much!