Ten short lessons on finding your way by the stars, each one animated against the real sky. Every lesson below is played out on screen; this is what they say.
Lesson 1 of 10
Because the earth rotates around its north-south axis, the northernmost point and southernmost points in the sky stay fixed throughout the night.
In the Northern hemisphere, we use Polaris, also known as the North Star. It's the star at the end of the Little Dipper's handle, a constellation also known as Ursa Minor.
In the Southern hemisphere, there is the Southern Cross, also known as the constellation Crux. It's four unusually bright stars, and it wheels around the southern point through the night rather than sitting on it, but its long axis always points towards the celestial south pole.
Lesson 2 of 10
You can find Polaris by finding the Big Dipper (aka Ursa Major), and taking the two stars at the end of the bowl and following them across the sky until you've hit Polaris.
Lesson 3 of 10
There is no bright star over the south pole of the sky. Instead, find the Southern Cross - 4 bright stars in a cross shape - and follow its long axis downwards about four and a half times its own length.
Lesson 4 of 10
Once you've found Polaris (north) or the Southern Cross (south), you know your hemisphere. But you can also use them to find your latitude. The higher they are in the sky, the farther you are from the equator.
On the equator Polaris sits on the horizon; at the pole it is straight overhead. Watch it climb as we sail north.
Lesson 5 of 10
The same measurement works south of the equator, with one extra step: there is no star on the pole, so follow the long axis of the Cross first and measure the empty point it leads you to.
On the equator the celestial south pole sits on the horizon; at the pole it is straight overhead. Watch it climb as we sail south.
Lesson 6 of 10
Now that we know our latitude, we need our longitude.
The first thing to notice is that if we see stars, it must be night! So we have to be in a dark area of the globe. The game gives the local time of each area you click on, so if it's daytime, it can't be the right answer.
Lesson 7 of 10
The stars around the celestial pole rotate around it once a day. You can use this to treat it like a 24-hour clock - you just have to know its orientation. The orientation is based on both your location and the time of year.
In the north the hand is Ursa Minor, the Little Dipper. In the south, the Southern Cross does the same job around the empty pole.
Lesson 8 of 10
The “clock's” orientation changes throughout the year.
The game's date is always today. You'll need to remember how the “clock” is oriented for this time of year. The date says where the dial starts; the hand says how far past that you are. Together they are your local time.
Lesson 9 of 10
Here is the payoff. These three places sit at the same latitude, and this is one single instant — the very same moment for all three. The hand reads differently at each.
Madrid and Denver are 101 degrees of longitude apart, and their hands sit ~seven hours apart on the dial.
So: read the hand, and with the date it gives you your local time. Then hunt along the map for a longitude whose local time matches. The game prints the local time of everywhere you click, so you can check before you commit.
Lesson 10 of 10
Everything from here on is yours. Drag the pin anywhere on Earth and the sky will travel with it; move the clock and the whole thing turns, fifteen degrees an hour.
Some things to go looking for. Slide north and watch the pole marker climb by exactly the degrees of latitude you gain. Cross the equator and watch it sink and come back up on the other side of the sky. Hold the clock still and slide east instead — the sky changes just as much, which is the whole reason longitude needs one.
The shadow on the map is real night. Drag into the lit half and the stars go out, because they would.