E1 Astrophysics E1 - E2.4

A light year is a unit of measurement used in astronomy to describe the distance that light travels in one year. It is not a measure of time, as stated in the other options. The speed of light is approximately 299,792,458 meters per second, so in one year, light can travel about 9.461 trillion kilometers. This distance is used to understand the vastness of the universe and to measure astronomical distances.

Hydrogen fusion in the core is the correct answer because it is the process by which stars generate energy. In the core of a star, hydrogen atoms combine to form helium through nuclear fusion. This fusion reaction releases a tremendous amount of energy in the form of radiant energy, which is what provides the heat and light of the star. Hydrogen combustion in the core or shell, as well as hydrogen fusion in the shell, are not accurate explanations for the energy source of most stars.

The correct answer is 100,000 LY. The diameter of our galaxy, the Milky Way, is estimated to be around 100,000 light-years. This means that if you were to travel at the speed of light, it would take you 100,000 years to traverse the entire diameter of the galaxy.

Comets are made of frozen ice, such as water ice, and various gases, including carbon dioxide, methane, and ammonia. These substances make up the nucleus of a comet. As a comet approaches the Sun, the heat causes the ice to vaporize, creating a glowing coma around the nucleus and forming a tail. The presence of these gases in comets is important for studying the composition and evolution of the solar system.

The most important thing about a star that determines pretty much everything about it is its mass. The mass of a star determines its temperature, luminosity, age, and even its life expectancy. The mass of a star influences the rate of nuclear reactions happening in its core, which in turn determines its temperature and luminosity. Additionally, a star's mass affects its lifespan, with more massive stars having shorter lifespans compared to less massive ones. Therefore, the mass of a star plays a crucial role in shaping its characteristics and overall behavior.

The rotation of the earth on its axis causes the apparent effect of stars moving around the pole star. As the earth rotates, it gives the illusion that the stars are moving in a circular motion around the pole star, which is located near the North Celestial Pole. This phenomenon is known as the diurnal motion of the stars and is caused by the earth's rotation.

Galaxy clusters are the largest gravitationally bound structures in the universe. They consist of hundreds to thousands of galaxies held together by their mutual gravitational attraction. These clusters are enormous in size, spanning millions of light-years across. The gravitational force between the galaxies keeps them bound within the cluster, and the immense mass of these clusters influences the formation and evolution of galaxies within them.

When comparing two stars, the luminosity is directly proportional to the mass of the star raised to the power of 3. Therefore, if a star has twice the mass of another star, its luminosity will be 2^3 = 8 times greater.