FirstLight Astronomy Club

33°29.6'N / 117°06.8'W / 1190 ft.

Let There Be (Less!) Light - Part 1

Have you seen the space image of the earth at night? It is actually a collection of cloudless satellite images taken of our planet in darkness, all sewn together, to give an overall global glamor shot of our planet in the dark. It is fascinating seeing the United States all lit up, with major highways showing up like glowing arteries. One can see how some countries are fully wired, others are quite dark. (Search "satellite images earth at night" online.)

But there is a dark side to all this light. What you see in the satellite image is light that is wasted, light that is not doing the job of illuminating only objects on the ground. What is worse than all this squandered energy is this: It is robbing us of our starlit skies. 

We who have been to both the uninhabited desert and the busy cities know well the difference in the night skies between the two - it's like night and day. One brought up in or near cities is barely aware of a night sky at all. Sure, there is the Moon and some of the brighter planets. Some may even be aware of the brighter stars like Sirius and Antares and Vega. But you have probably heard these people (if you are not one yourself) exclaim after having come back from vacation in a faraway place away from city lights, that the night skies there were "awesome" or "amazing." Most were not aware that there were so many stars, as if a dark night sky was as foreign to them as was their terrestrial destination.

All this is a shameful reflection of our times. These last few generations are the first since humans have walked the planet that have missed the complete beauty of the starry heavens. And we have no one to blame but ourselves. 

As you drive or walk around in the next few nights, observe our lighting. See how billboards are lit from the bottom up and how much of the light bleeds out skyward. See how that neighbor's lighthouse beacon of an outdoor lamp is lighting up way more than necessary for safety. Notice just how many lights are pointed up at their targets. See how many are purely cosmetic with no safety function at all. 

These are the culprits that are causing our night skies to glow eerily, that are stealing the heavens from us and our kids. But what can we do about it? Is there anything? Yes - a lot. Next time here we will look at things you can do in your own home - and in your city - to reclaim our skies.

Proximity Matters in Planetary Real Estate

If you asked your friends what time of the year the Earth is closest to the sun, during winter or summer, I'd bet that most of them would say during summer. After all, we are hottest during the summertime, therefore we must be closer. Correct?

The reasoning seems airtight. But it presumes that our distance determines our seasons, and it neglects the fact that our southern hemispheric friends are experiencing a cold winter at the same time we're having our hot summer.

The fact is that for these last couple weeks we have been the farthest from the sun in our orbit. And it is in the dead of our winter that we are closest to the fires of our star. Huh?

As you know, every planet, comet, and space rock in our solar system orbits the sun. But despite the fact that planetary orbits are drawn as perfect circles in our textbooks, they are not.

But that's OK. We don't need a perfectly circular orbit. Slightly oblong - we call it "elliptical" in the Land of Science - is just fine. But here's the point: Since it is not a perfect circle, it follows there must be a time in an orbit when a planet is closer to the sun than at all other times, and another time when it is farthest.

And it is now, at the beginning of July, that we are at our farthest. This "farthest point" in an orbit around the sun has a name, aphelion. Our closest point to the sun happens in the first week of January. Then we are at perihelion.

Now a fair question is: Why aren't we freezing right now, being farther away? Well, the difference between our aphelion and our perihelion isn't that dramatic. Our orbit, although not a perfect circle, comes close. There is a difference of only a few million kilometers between the two. But we are so far out that a couple million klicks doesn't matter.

Here's an analogy: Suppose you are a hundred yards away from a bonfire. If you were to take a big step closer would you feel the temperature rise? How about a step farther away? Would you feel a lot colder? Probably not.

Same with the sun. Our tiny difference in aphelion and perihelion makes no traumatic change in climate over the year. It is our tilt that gives us our seasons. The important question is: Are we tilted towards the sun or away? We are tilted towards the sun now, hence we have summer.

Don't get me wrong! Any more elliptical, or an average distance any closer or farther from the sun means very bad times on Planet Earth. But as it stands now - from tilt to spin to distance - all is very, very good.

Temecula Valley High School / Temecula, CA · Some images © Gemini Observatory/AURA Contact Me