Formation And Explanation Flashcards
How many stars does a galaxy typically contain?
One billion stars
How many galaxies is the Universe thought to contain?
Over one hundred billion
What are stars mainly made of?
Hydrogen and helium
What does hydrogen exist as in a star’s centre?
Nuclei (not atoms or molecules).
How does nuclear fusion happen in stars?
Hydrogen nuclei are positive so normally repel each other.
The temperature of a star’s centre is more than 15 million degrees.
This means the nuclei move very fast.
They collide to form a heavier nucleus: helium.
Vast quantities of energy (electromagnetic radiation) are released.
How are stars formed?
Clouds of hydrogen and dust are called stellar nebulae.
The particles coalesce due to gravity.
The clouds become more and more dense.
Hydrogen particles begin to spiral inwards and temperature rises to about 15 million degrees.
Nuclear fusion begins and the star is born.
What main force forms stars, galaxies and planets?
Gravity.
How are planets formed?
As a star burns, it pulls dust particles closer to it.
They are pulled more strongly as they have more mass.
They coalesce to form the inner rocky planets (Mercury, Venus, Earth and Mars).
This process is called accretion.
Gas particles have less mass so they are left further out.
They coalesce to form the gas giants (Jupiter, Saturn, Uranus and Neptune).
What are Pluto and Ceres believed to actually be, as opposed to planets?
Captured asteroids.
Why do planets orbit the Sun in the same plane and direction?
The gas and dust clouds originally spiralled in the same direction.
What does a star do to planets formed around it?
Catch them in its orbit. This is due to gravity.
Why does the Sun remain the same size?
The inward gravitational force equals the outward force of radiation pressure (which is due to thermonuclear explosions).
What model is mostly accepted that explains the origin of the Universe?
The Big Bang Theory
When did the Big Bang occur?
About 13.8 billion years ago.
From what did the Big Bang occur?
A tiny point called a singularity.