Astronomy is the oldest science and it shouldn’t come as a surprise that celestial navigation dates back to Homer’s Odyssey. Sailors would use the Sun during the day to find true north, the constellations at night to find direction, and a tool called a sextant. You have probably heard of it as it’s been around for a very long time and it was used by the Apollo astronauts to navigate their spacecraft and confirm their location. The sextant backdates to early 18th century, however, there is a bit of a disagreement as to who, in fact, created it.
The principle of how the device works was found in the unpublished writings of Isaac Newton, but it is mainly believed that John Hadley and Thomas Godfrey around 1731 brought forward the first ever design. However, the Englishman John Bird can be credited with the creation of the first sextant in 1757. Here is how the device works. The sextant allows celestial objects to be measured relative to the horizon, rather than relative to the instrument. The measurement of this angle, or the altitude, is known as sighting or shooting of the object. This angle represents a position line on a nautical or aeronautical chart. The sextant can also be used to measure the lunar distance between the moon and another celestial object and was used by the Apollo astronauts to chart the correct course. Astronauts back then had to calculate their own course and also had to learn the names and positions of a lot of stars in the sky, in order to be able to navigate through space.
Source: Air and Space
Find Your Way Home in the Northern Hemisphere
Chances are you won’t have a sextant with you when you go out stargazing. For an even better time, I recommend you leave your phone’s GPS out of this too. Look up and try to find your way. The first thing to do is to try and locate the North Star.
It is a well-known fact that Polaris is the one star that holds still in the Northern Hemisphere. Used by sailors and aviators to find direction and a popular choice amongst astrophotographers, Polaris hasn’t always been our North Star. The place the north pole points at changes over time, this is called stellar precession and it happens because of the Sun’s gravity. Polaris came to be our North Star around AD 500 and will continue to be the closest star to Earth’s north pole until AD 3000, so we still have a good few years to rely on Polaris for direction and some breathtaking star trail images.
So, why does Polaris stay in the same place in the night sky? The North Star is located one degree off of the side of the north celestial pole and as the Earth rotates on its axis, the stars move in a circle around us and also spin around Polaris. The farther north you would go, the higher Polaris will appear for you and the farther South you travel from the North Star, the lower it appears in the night sky.
The two constellations you can use to find Polaris are the Big Dipper and Cassiopeia. They rotate around the North Star and never really set, just change their place in the sky.
The easiest way to find the North Star is by finding the Plough, also known as the Big Dipper or the Saucepan. Follow the two outermost stars in the bowl and they will point you directly to Polaris. The Plough rotates anti-clockwise relevant to Polaris and it will appear in different places because of it. However, its relationship with the North Star never changes and you can always find it in the night sky. Cassiopeia is also a very useful constellation when trying to locate the North Star. You can find the Queen on the opposite side of the Plough, circling Polaris. It is usually found very high in the sky if the North Star is low or obscured.
Also, don’t forget that all stars in the sky rise in the east and make their way westward across the sky, like our Sun. This is due to the fact that the Earth spins on its axis towards the east.
However, if you are in the Southern Hemisphere, Polaris won’t be of much use to you. Instead, you should be looking for the Southern Cross in order to locate the South Pole. The Crux is the smallest of all constellations and is easily visible throughout the year. Alpha and Gamma, or Acrux and Gacrux are commonly used to mark south. The constellation Centaurus is used as a pointer and allows people to easily find the Southern Cross asterism.
So, next time you’re lost, have no GPS or a compass, don’t forget to look up – a star or two might be able to help you find the right direction.