Stars

Eventually, the hydrogen that powers a star's nuclear reactions begins to run out. The star then enters the final phases of its lifetime. All stars will expand, cool and change colour to become a red giant or red supergiant. 

What happens next depends on how massive the star is.

All the energy in a star is made in its centre (its core), by a process called nuclear fusion. The star releases the energy as heat and light. This is what makes a star shine. The outward force generated by the fusion process is balanced by the inward pull of the star's gravity. It is the balance between the two which stops the star from collapsing or expanding.

(1) Luminosity 

This is a more physical measurement. It measures the energy output of the object. This is done by looking at how much light is given out by the object over time. 

The units of luminosity are more standard, given in Watts - much like a light bulb! A typical LED light bulb in a house might be 20 Watts - the Sun is 20 million billion billion (2 x 1025) times brighter! 

A nucleus sits at the centre of an atom. It was only found in 1911 by New Zealand physicist Ernest Rutherford. The nucleus contains 2 types of particles known as neutrons and protons.

The proton has a positive electric charge. The neutron has no charge at all. Between them, they make up most of the mass of an atom as the surrounding electrons are tiny in comparison.

Stars

What we know about stars has changed over thousands of years. Early astronomers recorded the positions and numbers of stars. They did not think that stars could change. The first catalogue of stars was made by Chinese astronomers Gan De and Shi Shenfu around 400 BCE. Astronomers soon realised that 'new stars' could appear in the sky. We know these now as supernovae. The final explosion of a massive star's life.

Early Life

Claudius was born in Alexandria, Egypt, which was part of the Roman Empire at the time. 

Very little is known about his life. The information we do have has been taken from the books he wrote. 

Early Life

Cecilia was born in Wendover, England. Her mother was interested in lots of different topics like nature, music and theatre. Cecilia spent lots of time reading in her home's library.

At the age of 19, she won a scholarship to Cambridge University to study science. During that time, Cecilia went to a talk given by Arthur Eddington. Arthur talked about his recent trip to Africa to observe the stars near a solar eclipse. This sparked Cecilia's interest in astronomy.

Early Life

There is very little known about Gan De’s life and work, but we do know he was one of the first Chinese astronomers.

Career Highlights

Gan De wrote at least 2 books: ‘Treatise on Jupiter’ and ‘Astrological Predictions’. His books have since been lost and are no longer available. We know about his work because later astronomers have made reference to it.