This article is from the In-Depth Report The 2012 Transit of Venus
Science Talk

The Transit of Venus, Part 2

Mark Anderson, author of the book The Day The World Discovered the Sun, talks about the transit of Venus coming up on June 5th or 6th in different parts of the world and how it will be of use to astronomers searching for exoplanets

Podcast Transcription

Steve:         Welcome back for Part 2 of this Science Talk podcast conversation with author Mark Anderson about the Transit of Venus posted on May 31st, 2013. I’m Steve Mirsky.

In Part 1 Mark talked about some of the science and adventure of the transit missions back in the 1760’s. In Part 2 we’ll talk about the 2012 transit coming up next week and the actual new science it will enable astronomers to perform.

It’s interesting, in the book you quote Cassini, who if people have heard the name it’s probably because of the Cassini Expedition to Saturn that happened in the last decade. But Cassini, who lived at this time, warned everybody that there would probably not be a better opportunity to observe a Venus transit until about 2012, which I just thought was a fascinating little tidbit of history considering that we’re in 2012 and the transit he was talking about is next week.

Anderson:         Yeah. Cassini was actually a, there’s a whole family of legendary astronomers in France named Cassini, and I don’t know which one the probe is named after, but this was certainly a noteworthy and legendary Cassini who made that observation around I think it was like 1771 or so and saying this is, these transits are so rare. And science was able to forecast so far into the future when these transits would happen that he looked ahead and he said, you know these transits that we might see in the 19th Century - this is a guy in the 1770’s who is saying this, yeah, they’re not going to be so good. And the 2004 transit, again a guy in 1771 looking forward to the year 2004 says, yeah, not as good, but the one in June of 2012 that’s, that really will be the next one when we get the opportunity to do the kind of science that we did in 1769.

Steve:         And there actually, at the very end of the book you answer a question that I had throughout the book, and that is is there any actual new science to be done or is this just a nostalgia trip to see an actual transit of Venus?

But you talk about the fact that there is still new research to be performed that could really inform our search for new planets around other stars.

Anderson:         Absolutely. Yeah. Yeah. The transit of Venus turns out to provide new windows on the universe to each generation that gets to observe one. This time around of course we know the distance scales of the solar system. We know how far the sun and all the planets are.

However, now we’re looking at planetary systems elsewhere in the galaxy, and we want to understand what they’re like, and maybe even find sister earth’s elsewhere in the galaxy, and study not only the planets themselves but their atmospheres and everything else that we can find out.

Well transits, when a planet crosses directly in front of a host star, are tremendously useful. In fact they’re essential to finding these what are called exoplanets, in other words they’re planets outside of our solar system. And there are around 770 exoplanets that are known and they’ve really only been discovered in the last 20 years as astronomy has gotten very good at that.

NASA even has its own dedicated exoplanet space telescope called Kepler, and they find new exoplanets at the rate of a few per month, sometimes a few every week. So they’re finding these things left and right, and the way they find them is looking for tiny little dips in the light that comes, that we measure from a star that might represent a little eclipse of a planet passing directly in front of that star. And if you can see it on a periodic basis then you know okay, well that’s a planet that’s crossing it on a, in some sort of regular fashion.

So that’s, that’s all well and good if we just want to look at the planets, but if we want to actually look at the atmospheres and understand what’s on that planet, you can do that with a transit. And so what we know today, ‘cause we’ve sent space probes to Venus and we’ve studied the Sun very well, so both systems are pretty well understood, that is Venus and the Sun.

So there are going to be telescopes all over the world. Indeed the Hubble Space Telescope is going to be looking at the reflections of the Venus transit off of the moon. They can’t point the Hubble directly at the Sun because it would burn out its optics. But Hubble will also be looking at the Venus transit courtesy of the reflections of the moon. And what they’re all going to be looking for is the about .001 percent of the Sun’s light that has also passed through the atmosphere of Venus during the transit.

Steve:         [Inaudible]

Anderson:         The reason that’s interesting to astronomers is they can work backwards from that light and figure out well what is the chemistry in Venus’s atmosphere. What, they can even find the wind speeds in Venus’s atmosphere at the time of the transit. So they can find, they can actually perform a weather forecast of Venus.

Now that might be, it’s kind of interesting, it’s kind of an interesting curiosity about what we can use the Venus transit for, but we can’t do anything like that for planets in faraway star systems except for transits.

So what the Venus transit allows us to do is to study a known system, where we know Venus, we understand it’s atmosphere relatively well. We understand the Sun’s light relatively well. The one thing we don’t have a good picture of is what does it look like when Venus transits directly in front of the Sun and we study that light very carefully.

Then you can take the things that we learn from studying the transit of Venus and apply it to a transit of another planet elsewhere in the galaxy, and maybe even some day study its atmosphere, perform a weather forecast from halfway across the galaxy of some sister earth.

Steve:         Just by looking for the light as it goes through the sliver of atmosphere versus the bisque of the planet itself?

Anderson:         That’s right. Yeah. Yeah. See because we can get just, you get a tiny little bit of the light, during a transit you get a tiny bit of light that passes through the planet’s atmosphere, if it has an atmosphere. And so if you tease that out then you can start doing all kinds of interesting science on the atmosphere itself.

And again, we can send probes, and we have sent probes to Venus and to other planets to study, to study them up close, but we can’t do that for these far away planets. So that’s why the Venus transit is really helpful because it let’s us do kind of a test case where we understand all the parameters and then we apply all that knowledge to studying these planets elsewhere in the galaxy.

Steve:         So you must be particularly excited to be able to see this transit coming up next week.

Anderson:         Oh it’s, yeah, I mean it’s, it’s interesting as a piece of kind of cutting edge science today. I think it’s also, I think there’s also something a little more, there’s something just fascinating in and of itself that when you look at the Sun in the sky - and it’s important to note when you are looking at the transit, when you’re looking at the Sun at all you should be using some kind of solar filter, or there are different ways of observing the transit. I talk about that on my website, the book’s website on - so when you look at the Sun through one of these methods, like through a solar filter or something like that, it’s kind of, it’s kind of amazing.

You’re looking at this, at this star, this black, when you look at it through a solar filter it’s a black background, and then there’s this big yellow disc right in the middle, and it’s kind of this beautiful perfect sphere that you can understand why people have been studying the Sun for as long as they have, and that is fascinating.

But when you’re actually, when you see this little, this little circle cross it, like a June bug crossing a dinner plate, I mean it really, it really to me it really brings it home, this is just another star. This is, this is the kind of stuff that we see with stars all over the galaxy. What we’re looking at is, it’s kind of a humbling moment as you realize that, as Douglas Adams put it, that the universe is very, very, very, very big and we’re just a small piece of that much larger puzzle.

And so to me there’s, the Venus transit also has a way of kind of bringing it all home.

Steve: And where will you be watching it?

Anderson:         Yet to be determined, but there’s a number of media outlets that are talking about the Venus transit, so I’m going to be doing some interviews during the day. But probably I’ll end up going to one of the local Venus transit events where I live in Western Massachusetts.

Listeners would be well advised to do just a little bit of homework in advance, because the, it’s probably just as quick as doing a Google or two, finding local astronomy clubs or colleges, high schools that will be setting up their telescopes, ‘cause it is best to observe the Venus transit through a telescope ‘cause then you can see it right up close.

And again you can’t look at the, you can’t look at it directly without a good solar filter on your scope, but you let other people do that and then you can just go in and watch it with everyone else. And it’s really, I think it’s, it will be really, it will be really cool.

Steve:         And I think that there’s almost nothing that people with telescopes like better, well the first thing they like to do is look through their telescope, but the second most favorite thing they love to do is have you look through their telescope. So they are usually pretty generous about letting a lot of people take a look at whatever it is they’ve got the telescope trained on.

Anderson:         Here. Here.

Steve:         Well I wish you clear skies. That’s the important thing.

Anderson:         Boy. Yeah. If we, if we get cloudy skies you can at least watch a video on YouTube and see how someone else who had clear skies saw the transit. These people back in 1769, their whole world was riding on clear skies.

Steve:         We’ll be back right after this word from Kerry Smith at the Nature Podcast.

Female:         This week painting a molecular canvas, why birds look like baby dinosaurs, and should we try to save the endangered Sumatran rhino.

Announcer:         Just go to If Part 1’s tales of Long Ocean Voyages sounded interesting –

Announcer 2:         Set a course for adventure and expand your mind on a Scientific American Bright Horizon’s cruise. For information go to


Steve:         That’s it for this episode. Enjoy the transit wherever you are and however you observe it safely, and check out our website for lots of Venus transit info. On June 5th our Astronomy Editor, George Musser is scheduled to host a live chat about the transit so look for that.

And check out the free iPhone Venus Transit app from Astronomers Without Borders.

For Scientific American Science Talk I’m Steve Mirsky. Thanks for clicking on us.

[End of Audio]

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