Space Physics and Astronomy - SS1 Physics Past Questions and Answers - page 2

The planets in our solar system formed from a spinning disk of gas and dust called the solar nebula. As the nebula collapsed under its own gravity, it formed a central protostar (the Sun) and flattened into a disk. Within this disk, small particles collided and stuck together, forming planetesimals. These planetesimals further collided and accumulated mass, eventually forming the planets. The planets can be classified into two groups: the terrestrial planets (Mercury, Venus, Earth, and Mars) which are small and rocky, and the gas giants (Jupiter and Saturn) and ice giants (Uranus and Neptune) which are large and composed mainly of gas and ice.

Earth's Moon is the only natural satellite of the Earth. It has a rocky composition and lacks an atmosphere. The Moon's gravitational pull causes tides on Earth. It also has a significant influence on the Earth's axial tilt and stabilisation of the planet's rotation. The Moon has been a subject of scientific study and exploration, and it played a crucial role in the history of space exploration and human achievements.

Stars are luminous celestial bodies that are primarily composed of hydrogen and helium gas. They form from large clouds of gas and dust called nebulae. The force of gravity causes the nebula to contract and form a dense core, leading to the ignition of nuclear fusion, where hydrogen atoms fuse to form helium and release vast amounts of energy. This energy creates the light and heat emitted by stars. Throughout their lifecycle, stars go through different stages based on their mass, from the main sequence to red giant, supernova, and either white dwarf, neutron star, or black hole, depending on their mass. The exact fate of a star depends on its initial mass.

Galaxies are large systems of stars, gas, and dust held together by gravity. They come in various shapes and sizes. The main types of galaxies are spiral, elliptical, and irregular. Spiral galaxies, like our Milky Way, have a distinct spiral structure with a central bulge and arms that extend outwards. They contain young stars, dust, and gas. Elliptical galaxies are more rounded and lack the spiral arms. They consist mainly of old stars and have less gas and dust. Irregular galaxies do not have a regular shape and can be chaotic in appearance. They often contain young stars and exhibit ongoing star formation activity.