What is star? What is a constellation? Draw a three-dimensional object from different perspectives. Look at Big Dipper, Orion and Cassiopeia and change the perspective: http://nautil.us/issue/19/illusions/a-quick-spin-around-the-big-dippers. Look at the Orion Constellation in 3D: https://www.youtube.com/watch?v=lD-5ZOipE48 A star is a luminous sphere of plasma held together by its own gravity. They produce energy by nuclear reactions and emit light. The nearest star to Earth is the Sun. Constellations are imaginary patterns that farmers, poets, navigators, or astronomers invented to easily identify stars. Stars are big balls of burning gases that emit light and heat. During the day, the light coming from our closest star, the Sun, is too strong to see the other stars. During the night, when it is very dark, we can see from 1000 to 1500 stars. It would be very hard to tell which star is which by looking just at one! Constellations, with their familiar shapes, help localize stars and allow us to find our way through the night sky. The ancient Sumerians, and later the Greeks as Ptolemy classical 48 constellation in the Almagest, established most of the northern constellations in international use today. A constellation is formally defined as a region of the celestial sphere, with boundaries laid down in 1922 by the International Astronomical Union (IAU). There are 88 constellations across the sky between the northern and southern hemispheres so some constellations are only visible in one hemisphere. Stars belonging to a constellation are not on the same plane and can be at various distances from the Earth. Changing our position in the galaxy would change the relative positions of a group of stars, so we would see different constellations. Learn about 88 constellations: https://en.wikipedia.org/wiki/Constellation https://en.wikipedia.org/wiki/88_modern_constellations https://www.iau.org/public/themes/constellations/ See Graphics of all Constellations here: http://www.dibonsmith.com/graphics.htm Astronomers developed two methods to determine the distance of a star. The first one, known as parallax, uses triangulation. Astronomers observe the position of a star on one day (position 1 in the drawing below) and again six months later (position 2 in the drawing below). They can see the angle formed with the star and the Sun. Knowing that the diameter of the Earth’s orbit around the Sun is about 300 million kilometres, astronomers use trigonometry to calculate the distance. This technique works for stars within about 400 light years of Earth.

Constellations advice sailors and help astronomers. Constellations contain a huge variety of stars. Before the advent of modern navigation devices, GPS-and they even compasses, we have used the stars. Like signposts constellations can help us orient ourselves. They tell us the direction, distance and orient us. When we want to determine the location of land used coordinates - latitude and longitude. By latitude measure the distance between the north and south pole. The length is the distance in the other circle from east to west. We have celestial coordinate system. These coordinates are not called latitude and longitude. They are called declination and right ascension. They are extensions of earthly latitude and longitude designed to heaven. Ancient navigators used these imaginary lines to map the stars to navigate. They are not absolutely accurate, but it certainly helps sailors find the right path. Using a sextant, sailors could use Instructional stars like North Star to navigate. Sextant is a device used in marine navigation. By appliance equate the celestial body to the horizon and mark position. Then, with time and a digital scale sextant you can determine its position. Modern navigation using artificial stars - satellites. Following the creation of so on.. Artificial star is a GPS system. It can determine the position of the ship to within a few meters anywhere in the world. After they exchanged GPS-sextant, celestial coordinates are more important to astronomers than sailors. Although the coordinate system tells them where to focus their telescopes, the system has a serious flaw. It assumes that all stars are the same distance from us. Assumption, which is completely wrong. When you look at the stars in the night sky, it seems that everyone is the same distance from us. Although all seem equally remote, some are closer and others further.