Constellations and Asterisms

Constellations

A constellation is a pattern of stars as seen from Earth. They appear to be close to each other but can be far apart in space.
The International Astronomical Union officially recognises 88 constellations that cover the entire sky from the North to the South pole.
Some constellations, like Orion and Ursa Major, are visible from anywhere on Earth, although their position in the sky will vary depending on the viewer’s geographical location.
Constellations can be used to find other celestial bodies or for navigation. For example, the tail of the Big Dipper, which is part of the Ursa Major constellation, points towards the northern star Polaris.
Constellations change position in the sky across the year due to the Earth’s orbital motion around the Sun. Some constellations are only visible from certain parts of the world at different times of the year.

Unlike constellations, an asterism is a notable pattern of stars that isn’t officially recognized as a constellation.
Asterisms may be part of a constellation, like the Big Dipper is part of Ursa Major, or can span across multiple constellations.
The Summer Triangle, an asterism involving three bright stars from three different constellations (Deneb, Altair, and Vega), is prominent in the summer sky in the Northern Hemisphere.
The Winter Hexagon, another asterism, is seen in the winter sky in the Northern Hemisphere.

Because the stars in a constellation or asterism appear to move across the sky as the Earth rotates, their position can be used to tell time and direction.
Polaris, also known as the North Star, is approximately aligned with Earth’s axis of rotation, so it always appears directly above the North Pole.
If you can locate Polaris in the sky, you can determine which way is North and approximate your latitude.
Similarly, the relative positions of the stars in a constellation or asterism can be used to tell time. For example, you can estimate the time by noting the position of the Big Dipper relative to Polaris.