# The measurement of stellar parallax by Friedrich Wilhelm Bessel

## Stellar Parallax

The man’s attempt to determine the distance of stars from Earth has a long history. The Greek astronomer Aristarchus of Samos (320 BC-250 BC) and the Polish astronomer Copernicus knew that if the Earth revolved around the Sun, one would expect the stars to shift back and forth every year. The theory of Aristarchus almost completed the Kepler (16os- 17th c. AD), mystic and mathematician, proposed the elliptical orbits of the planets, argued that the Sun, “the center of the temple of God”, ensures the movement of the planets and formulated the laws of motion of celestial bodies, which Newton completed the “law of universal gravitation.”

The Aristarchos work ranks among the brightest minds in Greek and ancient world. The findings have enormous scientific value and leave astonished astronomers today, as no one can be sure how it was made. Unfortunately, Aristarchus and Copernicus never managed to observe the tiny parallax, and humanity had to wait until the 19th century. to be discovered.

These observations reached modern astronomy following a series of surveys and measurements, with the help of excellent organs of modern art. In fact the stars are much farther away than previously assumed, which justifies the fact that the stellar parallax is only detectable through the telescope use

The term stellar parallax refers to the apparent displacement of a star when seen from two different optical lines.
or is the angular displacement of the apparent position of a celestial object on the celestial sphere, due to the observation of the two locations very far apart.

Utilizing simple principles of geometry, this offset angle can be used to determine the distance of the star from the observer. One calculation of this distance is to determine the position of the star at a particular time of year. Half a year later, when the Earth will have rotated by half around the Sun, again measure the position of the star.

A nearby star will appear to move contrary to the most distant stars. The stellar parallax is similar to what one observes when closing one eye. Look at your hand with one eye and then the other. Your hand looks like it moves. The greater the parallax angle, the closer the object in your eye.

In 1830s, there was a passionate competition among astronomers about who would be the first to be identified accurately interstellar distances. The first stellar parallax was measured in 1838. Using a telescope, the German astronomer Friedrich Bessel (1784-1846) – was a friend of the maximum of German mathematics of Carl Friedrich Gauss, who also worked on astronomy – studied the star 61 Cygni J in the constellation Cygnus. 61 Swan showed significant movement, and calculations of the parallax Besel showed that the star 10.4 light years (3.18 parsecs) away from Earth. Awe is the fact that the first astronomers found a way to calculate the enormous interstellar distances without even removed from the garden of their home.

Because the parallax angle is so small for the stars, the first astronomers could use this approach only for the stars relatively close to Earth. In modern times, astronomers used the European satellite Hipparchus to measure distances over 100,000 stars.