so we decided to call Tina for help.

So this is where Tina works.

Yeah.

Let's go in.

Tina is our mentor in Science Club for Girls.

Okay, so this is the last flight of stairs until we reach the roof.

Oh, there's Tina!

Hi Tina.

Hey Tina.

Hi,ladies.

(Miranda) Tina is studying at Harvard, and she getting her Ph.D. in astrophysics.

We were out stargazing, and we couldn't see any stars.

We're not that far away from the city right now, being at the Harvard Astronomy Department, so the idea of problems with lights, exactly what you guys just said, is a big issue.

I'm an astronomer, I want to look at the stars.

And you guys couldn't see that many stars at all, right?

Having too many lights around prevents you from being able to see the stars up there.

♪ ♪ Light pollution is actually a really big environmental problem, not just for astronomers.

There's a lot of inefficient lighting.

So the different types of bulbs we use, then sometimes we lose a lot of light if it's pointing upwards rather than downwards-- things like that.

That's just a waste of energy-- that's why we call it pollution, because it's actually affecting our environment even though it may not be something tangible like chemicals in the water or something like that.

When you're looking at the earth from space you'll see large pockets of light glowing from the cities.

You can map out entire city areas and streets from space based on that.

There are very few areas that are completely dark.

(Izzie) Whoa, look at that-- the east coast and the west coast-- they're so bright!

(Tina) One of the big projects this year for the International Year of Astronomy is called The Great World Wide Star Count.

"The Great World Wide Star Count?"

Oh cool!

I'm really excited you guys came to me with this problem you guys had.

So you basically count stars?

Yeah!

The Great World Wide Star Count, what it's trying to do, it's trying to measure light pollution by counting stars.

So when you were at the park you can only see the brightest stars.

So the more faint stars you can see is actually a measure of light pollution.

We're not scientists, so how can we do this?

We can figure out a method to quantify light pollution and do this variable by star count, and therefore we're scientists.

You don't have to have a degree or anything to be a scientist.

As far as I'm concerned you're doing experiments, you're investigating things-- that's the definition of a scientist.

The constellation that I've chosen to do for The Great World Wide Star Count is the constellation of Cygnus, which is inside the Summer Triangle.

The Summer Triangle is made up of these 3 stars here.

There's Vega, there's Altair, and there's Deneb.

One of those stars is actually the tip of the constellation Cygnus.

So when we talk about stars and how bright they are, we refer to a magnitude system.

When we are talking about light pollution, we're taking about a limiting magnitude, Everyone who's participating in The Great World Wide Star Count will be using the same system.

So if there's a lot of background light, then these fainter stars in this constellation are not going to be visible.

Let's say we can't see any stars except the brightest star, and one of the brightest stars in the sky is Vega, so that will be an example where light pollution is really bad.

So this would be a limiting magnitude of 1.

Then going onward, other features become visible.

(Izzie) Hmm... 1, 2, 3, 4, 5.

Got it!

Eventually there's this interesting s-shaped pattern that happens in the middle of the cross.

If you can actually see that, then we're in good shape.

Then you get to a point when you really can't-- just too many stars to figure out anything.