Edexcel GCSE Physics: Astronomy

Stars form from clouds of gas and dust and then go through a life cycle that depends on their mass.

Describe and explain the life cycle of a star that is about the same mass as the Sun, from its formation to its final stage. In your answer you should name the stages in order, explain the role of gravity and nuclear fusion, and explain what keeps a main sequence star stable. (6 marks)

The table shows the average distance from the Sun and the orbital speed of four planets.

Planet	Distance from Sun / AU	Orbital speed / km/s
Mercury	0.4	47
Earth	1.0	30
Jupiter	5.2	13
Neptune	30.0	5.4

(a) Describe the relationship between a planet's distance from the Sun and its orbital speed, using the data to support your answer. (2 marks)

(b) Name the force that keeps each planet in its orbit around the Sun. (1 mark)

(c) State the direction in which this force acts on a planet. (1 mark)

Light from distant galaxies shows red-shift. Astronomers measure the wavelength of a particular line in the light from a galaxy and find it is longer than the wavelength of the same line measured in a laboratory on Earth.

(a) Explain what the red-shift of this light tells us about how the galaxy is moving. (2 marks)

(b) State what is observed about the red-shift of galaxies that are further away. (1 mark)

The Big Bang theory is the currently accepted model for the origin of the Universe.

(a) State one piece of evidence that supports the Big Bang theory. (1 mark)

(b) The cosmic microwave background radiation (CMBR) is detected coming from all directions in space. Explain how the existence of the CMBR supports the Big Bang theory. (2 marks)

A planet moves around the Sun in a nearly circular orbit at a constant speed.

Explain why the planet is accelerating, even though its speed is not changing. (2 marks)

Our Sun is a main sequence star.

Name the process by which the Sun releases energy in its core. (1 mark)