No Googling required!
Do you know how to determine your latitude — your position on Earth relative to the equator — without using the internet?
Would you like to learn? You never know when a skill like this could come in handy.
It’s really simple — all you need is a bit of basic spherical geometry and the stars. In the Northern Hemisphere, you need to find Polaris, aka, the “North Star.” You can find Polaris by locating the Big Dipper, or Ursa Major. Then, imagine a line connecting the two front stars of the Big Dipper continuing off to the upper right. The first bright star you come across is Polaris.
Here’s how to find your latitude. First, imagine you are standing right at Earth’s north pole. Where is Polaris? Directly overhead, and it will always be directly overhead with the whole sky appearing to rotate around it once every 24 hours.
Star trail photograph showing the apparent motion of stars around Polaris -- the bright star near the center, just above the jet trail. Photo credit: TedQuackenbush/Wikipedia (CC BY-SA 3.0)
Next, imagine walking south towards the equator — which is technically any direction. As you walk towards the equator, Polaris will start to move away from the point directly overhead towards the horizon. Once you make it all the way to the Equator, where is Polaris now? At the horizon.
To figure out your latitude, all you have to do is estimate the angle between Polaris and the horizon due north from where you are standing. For example, at Earth’s north pole, Polaris is directly overhead, which is 90 degrees above the horizon. This is also your latitude. At Earth’s equator, Polaris is on the horizon, or 0 degrees above it. Your latitude is 0 degrees.
If you are located in Boston, Massachusetts, Polaris is located roughly 42 degrees above the horizon, so your latitude is approximately 42 degrees north. It’s that simple!
But what if you are in the Southern Hemisphere where Polaris is not visible? You have to use the Southern Cross, or Crux. The Southern Cross is a constellation with many stars, but five are clearly visible. Mimosa is the bright star that forms the left-hand point of the Crux, Hip 59747 forms the right-hand point, Gacrux the top, Crux in the middle, and Acrux the bottom point.
Photo credit: Till Credner/Wikipedia (CC BY-SA 3.0)
The Southern Cross can be used for navigation since the longer bar of the Cross points almost exactly toward the South Pole of the sky, which unfortunately has the nickname the “south solar pit” because it is not marked by any bright star.
However, there also lies four other bright stars nearby that belong to two different constellations, Vela and Carina, which make up what is known as the “False Cross.” According to Space.com, it looks very similar to the true Southern Cross, and is even oriented roughly the same way. You just have to remember that the False Cross is located further north than the true one.
Once you locate the Crux, you can apply the same simple math trick.
h/t: The Math Dude
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