Viewer's Guide to the ISS

Did you know the International Space Station is easily visible to the naked eye? In fact, at it's brightest, it can outshine Venus! The problem is that it moves very fast (17,130 mph) so you need to know when to look, or you'll miss it.

So, how do you know when the ISS will be overhead? One great resource is Heavens-Above. It will tell you exactly when the ISS will be visible, how long it will be visible for, and where in the sky it will be. It also has information on lots of other satellites and other things of astronomical interest.

But sometimes it will be months before the ISS passes over your location at night. You'll need some kind of reminder after that long. That's the purpose of Spot The Station. Sign up for it, and it will send you an email 12 hours before the next sighting.

There are also apps for mobile devices that are very useful. A good one I just got is ISS Detector.

Also worth mentioning is Wolfram|Alpha. It's less practical for finding good viewings, but it has lots of interesting information. Not just about the ISS, not just about satellites, not just about astronomy, it knows about pretty much everything.

So, go out and look at the sky. It's an awesome place.

Ode to the ISS

Tonight, I saw a point of light in the sky.

It could have been a burning ball of hydrogen, millions of miles across, and trillions of miles away. But I knew it wasn't a star, because it was much too bright.

It could have been a ball of rock, brightly reflecting sunlight off its clouds of acid. But I knew it wasn't Venus, because it was moving much too quickly.

It could have been a bit of dust, falling to the earth a hundred times as fast as a speeding bullet. But I knew it wasn't a meteor, because it lasted much too long.

It was a structure the size of a football field, made of aluminum, titanium and silicon, over two hundred miles above our heads, always falling, but always missing the ground, current home to six. It was the International Space Station.

The Autumnal Equinox

We live on the surface of a giant spinning ball. From our perspective, everything else appears to move around us as we spin. The sun, the moon, the planets, the stars. As we spin to face the sun, it appears to rise the sky. As we spin to face away is appears to set. It is no coincidence that we spin around exactly once each day. It is our spinning that determines the length of the day.

But we don't just spin in place. As we spin, we move in a circle around the sun. But the way we spin is tilted compared to the way we move around the sun. And the direction we're tilted doesn't change as we move around the sun, which means that sometimes we're tilted toward the sun, and sometimes we're tilted away from it. When you're tilted away from the sun, the days are shorter and the nights are longer, which makes it colder. The winter solstice is the day when you're tilted exactly away from the sun. When you're tilted toward the sun, the days are longer and the nights are shorter, which makes it hotter. The summer solstice is the day when you're tilted exactly toward the sun. It is no coincidence we move around the sun exactly once each year. It is our moving around the sun that determines the length of the year.

Not to scale. Credit: NOAA

Keep in mind that when the northern hemisphere is tilted toward the sun, the southern hemisphere is tilted away, and vice versa. The summer solstice in the northern hemisphere is the winter solstice in southern hemisphere, and the winter solstice in the northern hemisphere is the summer solstice in the southern hemisphere.

But today, we aren't tilted toward the sun, or away from it. Today, we are tilted perpendicular to the sun. Today is the autumnal equinox, the day when the day is equal to the night.

The equinox is a time of change. It marks the midpoint in the transition from the summer solstice to the winter solstice. Beyond that, it is also an inflection point. After the summer solstice, the days get shorter. At first, only a little bit. One day will be only a few seconds shorter than the day before it. But over time, the change increases, until one day will be minutes shorter than the day before it. The solstice is the time of the fastest change. After the solstice, the days will continue to get shorter, but the speed of the change will slow down again.