Which shape is most common among galaxies in the universe and relationship between Earth's position around sun and the constellations that are visible at night?
Elliptical galaxies are the largest and most common galaxies observed.Perhaps the most familiar kind of galaxy is spiral galaxies. They have a distinctive shape with spiral arms in a relatively flat disk and a central "bulge". The bulge has a large concentration of stars. The arms and bulge are surrounded by a faint halo of stars. A second class of galaxy is the ellipticals. Like spirals, they are named for their shapes: they look like fat, fuzzy footballs. Instead of spreading out into a thin disk, as they do in spirals, the stars in ellipticals wrap completely around the galaxy's heart in all directions. Most of the galaxies we can easily observe are spirals (about 45%), 25% or so are S0, about 25% are ellipticals of various kinds, and a few % are irregulars. In actual fact, however, irregulars and especially (dwarf) ellipticals probably dominate the universe, but are too faint to be easily seen. These shapes are typically divided into elliptical, spiral, or irregular. The shape of a galaxy gives a clue to the age and types of star within the galaxy. Spiral galaxies have a central bulge of stars surrounded by a disk that contains arms, which form a spiral structure. The existing stars inside an elliptical galaxy tend to be older, giving off more red light than younger stars. So, why do astronomers think elliptical galaxies dominate the sky? Because when specific regions of the sky are studied in depth, more elliptical galaxies appear. As stars form in one region, the largest ones cause shock waves to spread through the interstellar medium, igniting the formation of new stars. This causes the star-forming region to propagate through the galaxy. Combined with the differential rotation of the galaxy, this makes spiral arms appear. Earth orbits around the Sun once each year. Our view into space through the night sky changes as we orbit. So, the night sky looks slightly different each night because Earth is in a different spot in its orbit. The stars appear each night to move slightly west of where they were the night before. 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. Stars make their own light, just like our sun (the sun is a star the closest star to Earth). But the stars are very, very far away from our solar system so they appear to be very tiny to us, even though up close they are large. 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. An Earth travels around the Sun; the nighttime side of Earth faces a different part of outer space. Because of this, different constellations are visible, depending on the time of year. But certain constellations can be seen all year long in some places because they are above the North Pole or below the South Pole. Compared with other stars, the Sun actually isn't that bright, but it looks very bright to us because it's much closer to Earth than other stars are. At night, when your side of Earth is facing away from the Sun, the only light that reaches you is from other stars. Because the sun is much closer to Earth than all other stars, it appears bigger and brighter. The sun's brightness overwhelms the brightness of all other stars during daytime, and that is why we can see only the sun during the daytime.