The astrolabe was the most important invention of the Age of Exploration, as seen through the facts that it could determine local time and latitude, measure the angles of stars, and locate the positions of the Sun, Moon, planets, and more components of astronomy.

Astrolabe, any of a type of early scientific instrument used for reckoning time and for observational purposes. One widely employed variety, the planispheric astrolabe, enabled astronomers to calculate the position of the Sun and prominent stars with respect to both the horizon and the meridian.

The astrolabe is a tool using the positions of the stars or sun. It was formerly used in navigation to help explorers and sailors figure out where they were. They found their distance north and south of the equator by measuring the distance of the sun and stars above the horizon.

An astrolabe is a device that uses astral bodies like the sun and stars to either tell your position in latitude or tell the local time. It can also be used to measure celestial events like the wobble of the Earth’s axis.

The mariner’s astrolabe was used until the middle or, at the latest, the end of the 17th century. It was replaced by more accurate and easier-to-use instruments such as the Davis quadrant.

Even though astrolabes are extremely ancient technology, they’re still in use today and people still learn to make them as part of learning astronomy.

An early astrolabe was invented in the Hellenistic civilization by Apollonius of Perga between 220 and 150 BC, often attributed to Hipparchus. The astrolabe was a marriage of the planisphere and dioptra, effectively an analog calculator capable of working out several different kinds of problems in astronomy.

The accuracy of astrolabes is limited because in ordinary use most of them cannot be read to less than about half a degree and because the scale varies with distance from the pole, expanding rapidly beyond the equator.

Materials List (per student)

1. 1 piece of cardboard, manila file folder, or other stiff paper.
2. 1 piece of dark thread or string 12 inches (30 centimeters) long.
3. 1 small weight, such as a metal washer.
4. 1 plastic drinking straw.
5. 1 copy of an astrolabe drawing.
6. 1 container of glue or paste.
7. 1 pair of scissors.
8. 1 roll of tape.

Claudius Ptolemy

How to Determine Your Latitude Using the Astrolabe

1. Locate the star Polaris at night.
2. Sight the star through the straw.
3. Note what degree the string lines up at on the protractor using the set of numbers from 0-90 degrees. This number is the zenith angle.
4. To find the altitude angle: 90° – zenith angle.

The quadrant is a very simple tool that allows the user to determine his or her latitude by measuring the altitude of a heavenly body. When used in celestial navigation or astronomy, altitude means the angle of elevation between the horizon and celestial bodies like the sun, planets, moon, or stars.

A sextant can measure an angle on any plane, and works by a principle of double reflection. An astrolabe can only measure angles in a vertical plane and was principally used for latitude-finding, although you can also use it for purposes such as finding the height of something.

In particular, the altitude of Polaris (NCP) = latitude of observer. Remember that the altitude of Polaris is 0 degrees if you are observing from the equator (0 degrees latitude) and 90 degrees if you are observing from the north pole (latitude 90 degrees), and it is also true for intermediate latitudes.

(30 degrees latitude)– Polaris is located 30 degrees above the northern horizon. This trend continues until the traveler reaches the geographic (not magnetic) North Pole. At this point (90 degrees latitude), Polaris is 90 degrees above the northern horizon and appears directly overhead.

If you took its picture, you’d find that it makes its own little circle around the exact point of the north celestial pole every day. That’s because the North Star is really offset a little – by about three-quarters of a degree – from celestial north.

Polaris is so far away (about 434 lightyears) that the rays of light approach the Earth in a parallel manner. This allows us to look at the angle between us and the star (which is the same as the angle between the horizon and the star) to locate our latitude on the Earth.

Low latitudes are those locations found between the Equator (0 degrees N/S) and 30 degrees N/S. The middle latitudes are found between 30 degrees N/S and 60 degrees N/S. And the high latitudes are found between 60 degrees N/S and the poles (90 degrees N/S).

90

North Pole

Polaris, the North Star, appears stationary in the sky because it is positioned close to the line of Earth’s axis projected into space. As such, it is the only bright star whose position relative to a rotating Earth does not change. All other stars appear to move opposite to the Earth’s rotation beneath them.

Bottom line: Every star rises and sets as seen from the Earth’s equator, but no star rises or sets at the Earth’s North and South Poles. Instead, as viewed from the poles, every star is circumpolar. Between the equator and the poles … you’ll see some circumpolar stars and some stars that rise and set daily.

There are 5 constellations in the sky (at this latitude) all night long every night of the year – Ursa Major, Ursa Minor, Draco, Cepheus, and Cassiopeia. These are the best constellations to start with because they are visible all year long.

Cassiopeia, Cepheus, Draco, Ursa Major and Ursa Minor can be seen all year long. In the winter, look for Canis Major, Cetus Eridanus, Gemini, Orion, Perseus and Taurus.

The stars are not fixed, but are constantly moving. If you factor out the daily arcing motion of the stars across the sky due to the earth’s rotation, you end up with a pattern of stars that seems to never change.

The first star-like object to become visible after sunset these days is no star. It’s the planet Venus. Venus is in the west and so bright you can see it easily before it’s completely dark. Probably the first star you’ll notice this time of year as the sky darkens is Arcturus.

Methuselah star

| Fomalhaut is sometimes called the Loneliest Star because no other bright stars shine near it in the sky. It appears in a part of the sky that’s largely empty of bright stars. For this reason, in skylore, Fomalhaut is often called the Lonely One or Solitary One. It’s an easy star to spot and one you’ll want to meet.