Astronomy Study Guide

Our Solar System encompasses a wide variety of celestial bodies gravitationally bound to the Sun. At its heart is the Sun, a medium-sized star that provides light and heat to the entire system. Orbiting the Sun are eight officially recognised planets, each with distinct characteristics and orbits. Many of these planets, including Earth, are accompanied by natural satellites, commonly known as moons. Beyond the planets, the Solar System also contains dwarf planets, which are smaller celestial bodies similar to planets but have not cleared their orbital path of other debris. Asteroids, mostly rocky bodies, are found predominantly in the asteroid belt between Mars and Jupiter. Comets, icy bodies that can develop visible tails when near the Sun, originate from the outer reaches of the Solar System.

The discovery of Cosmic Microwave Background (CMB) radiation provided crucial evidence that solidified the Big Bang theory as the most widely accepted model for the Universe's origin. Before its detection, the Big Bang theory predicted that the early Universe was extremely hot and dense, and as it expanded, it would cool down. This cooling process would leave behind a faint glow of electromagnetic radiation, stretched to microwave wavelengths due to the Universe's continued expansion. In 1964, Arno Penzias and Robert Wilson, while working with a new antenna, detected a persistent background noise that they could not eliminate. This noise was isotropic, meaning it came from all directions, and had a temperature of about 2.7 Kelvin, corresponding to microwave radiation. This accidental discovery perfectly matched the predicted properties of the leftover radiation from the Big Bang. The existence of CMB radiation, acting as a 'fossil' of the early Universe, strongly supported the idea of an initial hot, dense state, offering compelling observational proof that the Universe indeed originated from a singular, extremely hot event and has been expanding and cooling ever since. This discovery provided a more robust explanation for observations like redshift and the abundance of light elements, integrating them into a cohesive cosmological model.