lecture 3 Flashcards
(19 cards)
What is the root of the word ‘astronomy’?
The Greek word for ‘star’
Astronomy encompasses the study of the entire universe.
What is the most easily studied star?
Our Sun
The Sun is visible only in the daytime.
What role does the Sun play in relation to life on Earth?
Source of virtually all light, heat, and energy
Life on Earth could not survive without the Sun.
What is the main energy generation process in the Sun?
Nuclear fusion
This process supports life on Earth.
How did ancient peoples view the Sun?
As a god or a type of fire
They created mythologies to explain its daily rise and set.
What is the ancient misconception about the Sun’s composition?
That it was burning coal or wood
This was ruled out by scientific calculations.
What concept did scientists propose in the late 19th century to explain the Sun’s energy?
Gravitational contraction (Kelvin-Helmholtz contraction)
It suggested the Sun generates energy by slowly contracting in size.
What flaw did geologists point out regarding gravitational contraction?
Earth is far older than 25 million years
This meant gravitational contraction could not account for the Sun’s energy generation.
Who published the special theory of relativity that helped explain the Sun’s energy?
Einstein
His equation E=mc² shows that mass contains enormous potential energy.
What is the main nuclear reaction occurring in the Sun?
Proton-proton chain
This involves 4 hydrogen nuclei fusing to form a helium nucleus.
What particles are emitted during the proton-proton chain reaction?
Positrons and neutrinos
Positrons balance electric charge; neutrinos carry away energy.
Why does nuclear fusion only occur in the Sun’s core?
High temperatures (10 million degrees) and high density
These conditions allow protons to collide frequently enough to fuse.
What is the balance that prevents a star from contracting indefinitely?
Outward gas pressure equals inward force of gravity
This balance maintains stable equilibrium in a star.
What is the mass-luminosity relation?
More massive stars have greater luminosity
This is due to higher core temperatures and faster hydrogen burning.
What are the three main methods of heat transport in stars?
Conduction, convection, radiation
In the Sun, radiation is the quickest method, but convection is dominant near the surface.
What happens to the Sun after about 10 billion years?
It finishes burning hydrogen in its core
This leads to the star starting to contract again.
What is the red giant phase?
A phase where the outer layers expand after hydrogen burning
The star becomes a giant like Aldebaran or a supergiant like Betelgeuse.
What occurs during the helium flash in medium mass stars?
Helium fusion starts in a sudden explosion
It generates more energy than an entire galaxy for a short time.
What are planetary nebulae?
Expanding shells of gas blown off old giant stars
They are named because they looked like planets in early telescopes.
