Bad Astronomy | New research looks at what alien worlds might be able to find Earth

When I was a kid, and survived on a diet of 100% trashy sci-fi, I would sometimes go outside at night, look up at the stars, and wonder how many worlds were out there.

Yes! The Earth orbits the Sun in a flat ellipse. From our viewpoint that means the Sun moves around the sky once per year on a line, a literal reflection of the Earth’s orbit on the sky, which we call the ecliptic. Any stars in the sky close to the ecliptic would see the Earth transit the Sun once a year (well, once an Earth year) and could easily detect us*.

New research shows there are lots of them. And they make interesting targets for people involved with the Search for Extraterrestrial Intelligence (SETI). After all, if we’re looking for planets that are like Earth, and can support life — and maybe, hopefully, possibly, finding that life, even intelligent life — then there may come a time when we want to talk to them. Aliens living on planets close to our ecliptic might already know we’re here. That makes the first phone call a lot less awkward.

So how many stars are there like that?

Lead research author Lisa Kaltenegger explains:

Attempts have been made to make a list, but it’s not all that easy. First you have to work out the geometry; how far from the ecliptic can you be and still see the Earth transit? The trig isn’t too bad, and the answer is about a quarter of a degree, making a strip on the sky centered on the ecliptic half a degree wide (for comparison, and if you look at the geometry you’ll realize not uncoincidentally that’s about the same width as the Sun in the sky).

Source: Bad Astronomy | New research looks at what alien worlds might be able to find Earth