Stellar Evolution
All stars form in nebulae, huge clouds of gas and dust.
Though they shine for thousands of years, stars do not last forever. The changes that occur in a star over time and the final stage of its life depends on a star's size.
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.
Stars
Stars are massive, glowing balls of extremely hot gas (called plasma) in space. The Sun is our closest star.
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.
Brightness
Light is the main signal we receive from space. Almost everything we know about space has been found by measuring light.
One of the main ways to measure light is to look at the brightness. Measuring the brightness of something in space isn't as easy as you'd think though.
(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!
Nuclear Physics
Nuclear physics is the branch of science which looks inside atoms. It looks at the nucleus, and what effect different interactions have on it.
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.
Understanding our Universe
The universe has always amazed people. Over time, our understanding of stars and galaxies has changed a lot.
- 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.
Claudius Ptolemy
Occupation
Mathematician, Astronomer, Geographer
Year born
100 AD
Research Areas
Movements of planets and stars, Cartography
- 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.
Cecilia Payne Gaposchkin
Occupation
Astronomer
Year born
1900
Research Areas
Stars, Spectroscopy
- 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.
Gan De
Occupation
Astronomer, Mathematician
Year born
Around 400 BCE
Research Areas
Jupiter’s movements, Star maps, Sunspots
- 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.
Classify a Star
What is a star?
We can see thousands of stars in the night sky - small points of light in the vastness of space. But what are stars? How do they make light? Why are they different colours? Watch this video to find out some more information about stars!