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  • Writer's pictureLuke

Navigating the Northern hemisphere

The Big Dipper can be used reliably to find your way around the sky and around Earth as well. Here’s how:

step 1) Locate the Big Dipper

The Big Dipper is very iconic and with its bright stars it’s usually one of the first things to jump out at you. Currently look for the Big Dipper very low in the northern sky (slightly east of due north) just after sunset. Depending on the time of year at sunset, the Big Dipper ranges from in the north-east from February to March, high in the north from April to May, in the north-west from June to October, and very low on the northern horizon November to January.

step 2) Find the North Star (Polaris) with the Big Dipper

One of the reasons the Big Dipper is so iconic is because it has been used for centuries to find the North Star. The two stars that make the end of the vessel of the Big Dipper are called “the pointer stars” because they point at the North Star. Make an imaginary line with these stars and trace it until you run into another star of similar brightness to the pointers, this is the North Star. (it’s a common misconception that the North Star is a particularly bright star; it’s really of similar brightness to the stars in the Big Dipper).

step 3) Find north with the North Star

Now that you found the North Star all you have to do is drop a line directly down to the horizon from that star and that’s due north!

Step 4) find your latitude with the North Star

The North Star can also tell you latitude; all you have to do is measure what angle the North Star is above the northern horizon and that’s your latitude. There’s a very ‘handy’ way of doing this with the pointer stars (the stars at the end of the vessel of the big dipper). Hold your hand out at a full arms length and measure how many fingers fit between the pointer stars (usually three fingers). The pointer stars are almost exactly 5 degrees apart so now all you have to do is count how many fingers fit between the horizon and the North Star and you have a rough estimate of how far north you are on the planet.

For example Baseline Road in south Boulder is called “baseline” because it is surveyed to be on the 40th parallel. If three fingers fit between the pointer stars, you would find standing on the sidewalk of Baseline Road eight sets of three (or 24 fingers) fit between the horizon and the North Star proving Baseline Road is exactly 40° north.

Baseline Rd extending across Colorado as seen from Sunrise Amphitheater

Tip: for the longitude measurement to work you have to start on the true horizon. Imagine you’re on a boat in the middle of the ocean, where the water meets the sky is your true horizon. Do not use trees/buildings/mountains as the start of the horizon as measuring up any higher than the true horizon will make your measurement inaccurate.

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