Are all constellations visible from the Earth each night and why do constellations stay in the same place in the sky but planets move?
Are all constellations visible? No. The visible constellations change by season and where you are on the earth.
Constellations appear to move because the Earth moves. Planets are much closer to Earth and their motion is visible, though our perception of that motion is also confounded with the movement of the Earth.
Sadly, no observer on Earth can see all 88 constellations at once. Which star patterns one can spot at any given night depends on the time, season, the stargazer's latitude and, obviously, the observational conditions. There is no constellations visible all-year from the Earth's equator. By the same token, all constellations are visible at some point during a given year. A constellation is a group of stars that appears to form a pattern or picture like Orion the Great Hunter, Leo the Lion, or Taurus the Bull. Constellations are easily recognizable patterns that help people orient themselves using the night sky. There are 88 “official” constellations. During summer, in the Philippines, the constellations of Orion and Taurus are not visible at night. An astronomer noticed that the Sun and planets move across the sky and appear to travel along a set course that passed through a small belt of stars. The constellations in the band are known was constellations of the zodiac. On any night you can see from 5-6 of the constellations lined up after one another. Hydra is the largest of the 88 modern constellations, measuring 1303 square degrees, and also the longest at over 100 degrees. The stars are in the sky both day and night. During the day our star, the Sun, makes our sky so bright that we cannot see the much dimmer stars. At night, when the sky is dark, the light of the stars can be seen. The rotation of the Earth causes all the stars to appear to rotate at the same speed (very nearly) so that their positions relative to one another do not change. 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. That's because the Earth's axis points at a point in the sky around which everything appears to move, including the stars. In the North, this happens to be very close to a star called Polaris, or the North Star. It is in the constellation called Ursa Minor, or the Little Bear. The stars change their position but can be seen only after a long time due to substantial distance. Planets in orbits spin on their own axis and change their positions constantly. Stars consist of matter like Hydrogen, Helium, and other light elements. A planet's orbital speed changes, depending on how far it is from the Sun. The closer a planet is to the Sun, the stronger the Sun's gravitational pull on it, and the faster the planet moves. The farther it is from the Sun, the weaker the Sun's gravitational pull, and the slower it moves in its orbit.
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