(a) Stars and planets are two very different types of celestial objects. Stars, like our Sun, are massive balls of gas that produce their own light and heat through nuclear fusion. They can be very hot and can vary in size and brightness. On the other hand, planets do not create their own light; they reflect the light of a star, like how Earth reflects the Sun's light. Planets are usually solid or gaseous bodies that orbit stars and can vary in size, composition, and atmospheres.
(d) Galaxies and constellations also have different characteristics. A galaxy is a massive system made up of billions of stars, gas, dust, and dark matter, all held together by gravity. Our Milky Way is a galaxy containing our Solar System and millions of other stars. In contrast, a constellation is a group of stars that form a recognizable pattern in the night sky but is not necessarily related in space or distance. Constellations are often used for navigation and storytelling, while galaxies represent vast collections of stars and other materials.