Stars and the Universe

What does the term protostar mean?

Oct/Nov 2025

A teacher asks two students to explain redshift. Student 1 says: It is a reduction in the observed wavelength of electromagnetic radiation from stars. Student 2 says: It occurs because stars and galaxies move away from the Earth. Which students are correct?

Oct/Nov 2025

Fig. 9.1 illustrates the Sun and the rest of the Solar System travelling in a circular orbit around the centre of the Milky Way. Diagram labels: Milky Way, orbit about centre, centre of Milky Way, position of Solar System, 26 000 light-years. The Sun moves along this circular path with speed v. The speed of light in a vacuum is $9.5 \times 10^{12}$ km/year. The Sun lies 26 000 light-years from the centre of the Milky Way.

Oct/Nov 2025