Astronomy Study Guide

The Solar System consists of the Sun and the celestial objects gravitationally bound to it, including eight planets. Each planet orbits the Sun at a unique distance, and their order is a fundamental aspect of understanding our cosmic neighbourhood. This order, from closest to furthest from the Sun, is critical for identifying specific planetary characteristics and dynamics. Knowing the names and the precise sequence of these eight planets is a core component of astronomical literacy.

Red-shift is the phenomenon where electromagnetic radiation, typically visible light, from distant galaxies is observed to have longer wavelengths, or is 'shifted' towards the red end of the spectrum. This occurs because the universe is expanding, and as light travels from a distant galaxy to Earth, the space between them stretches. This stretching of space increases the wavelength of the light, causing it to appear redder. The greater the distance of a galaxy from Earth, the more space has expanded during the light's journey, resulting in a larger observed red-shift. This direct relationship between a galaxy's distance and its red-shift provides strong evidence for the Big Bang theory and the expansion of the universe.