Celestial body
Introduction
A celestial body, also known as an astronomical object, is any natural object in space outside the Earth's atmosphere. These bodies include planets, stars, galaxies, asteroids, comets, and nebulae, among others. They are the fundamental entities studied in the field of astronomy.
Classification
Celestial bodies can be broadly classified into two categories: luminous and non-luminous bodies. Luminous bodies are those that emit their own light, such as stars and galaxies. Non-luminous bodies, on the other hand, do not emit their own light and are visible due to the light they reflect from luminous bodies. Planets, asteroids, and comets are examples of non-luminous bodies.
Luminous Bodies
Stars
Stars are massive celestial bodies that emit light and heat due to the nuclear reactions taking place in their cores. The sun, the closest star to Earth, is an example of a star. Stars vary greatly in size, temperature, and age.
Galaxies
A galaxy is a gravitationally bound system of stars, stellar remnants, interstellar gas, dust, and dark matter. The galaxy that includes our solar system is known as the Milky Way. There are billions of galaxies in the universe, each containing millions to billions of stars.
Non-luminous Bodies
Planets
A planet is a celestial body that orbits a star, is spherical in shape, and has cleared its orbit of other debris. There are eight known planets in our solar system, each with unique characteristics.
Asteroids and Comets
Asteroids and comets are smaller celestial bodies that orbit the sun. Asteroids are made up of rock and metal and are mostly found in the asteroid belt between Mars and Jupiter. Comets, on the other hand, are composed of ice, dust, and rock and have highly elliptical orbits that bring them close to the sun and then back to the outer parts of the solar system.
Observation and Study
The observation and study of celestial bodies have been fundamental to the development of our understanding of the universe and our place in it. This field of study is known as astronomy, and it utilizes a variety of tools and techniques, including telescopes, spacecraft, and computer simulations.