10. Space Flashcards
Define luminosity
What symbol and units are used?
The rate of light energy released or power output of a star.
Symbol: L
Units: W or Js⁻¹
Define Intesity
What symbol and units are used?
The power received from a star (its luminosity) per unit area.
Symbol: I
Units: Wm⁻²
What about a star follows the inverse square law?
It’s intensity.
Showed by I=L/4πd².
(4πd² beacuse light from a star is assumed be emitted equally in all directions from a point.)
What is parallax?
The apparent change of position of a nearer star in comparison to distant stars in the background
Why does parallax happen?
Because the orbit of the Earth around the Sun.
How is parallax measured
Angle of parallax (θ).
by measuring the angle to a star and seeing how this angle changes as the Earth changes position.
What can you deduce from the angle of parallax about a star’s distance?
The greater the angle of parallax, the closer the star is to the Earth.
What is meant by Astronomical Unit (AU)?
The average distance between the centre of the Earth and the centre of the Sun.
What is meant by Parsec (pc)?
The distance at which the angle of parallax is 1 arcsecond (1/3600th of a degree).
What is meant by Light Year (ly)?
The distance that an EM wave travels in a year in a vacuum.
What is a standard candle?
An object of known luminosity.
How are standard candles used to measure distances?
By measuring the intensity detected from the light source on Earth and using the inverse square law equation to calculate its distance away.
What does a Hertzsprung-Russell (HR) diagram show?
The stellar luminosity of a star against its temperature
What can you infer from a Hertzsprung-Russell (HR) diagram?
What spectral class that star belongs to.
Where are Red Giants found on a Hertzsprung-Russell diagram?
Top Left
with red supergiants being at the very top
Where are Blue Giants found on a Hertzsprung-Russell diagram?
Top left.
Where are Main Sequence Stars found on a Hertzsprung-Russell diagram?
From top left to bottom right in a y=-x³ shape.
Where are White dwarfs stars found on a Hertzsprung-Russell diagram?
Bottom left.
What direction do the scales go on a Hertzsprung-Russell diagram?
X-axis: Temp Decreasing
Y-axis: Luminosity Increasing.
Both exponential.
What main feature dictates the lifecycle of a star?
Its mass.
How are protostars formed?
- Clouds of gas and dust (nebulae) have fragments of varying masses that clump together due to gravity.
- Irregular clumps rotate gravity/conservation of angular momentum spins them inwards.
- This forms a denser centre – a protostar.
What happens to form a main-sequence star?
- High temps and pressures allow for fusion.
- The inward force of gravity and the outward force due to fusion are in equilibrium – the star is stable.
- Hydrogen nuclei are fused into helium.
- The greater the mass of the star, the shorter it’s main sequence period because it uses it fuses at a faster rate.
What happens to form a Red Giant star?
- Once the hydrogen runs out, the temperature of the core increases.
- It begins fusing helium nuclei into heavier elements (E.g. Carbon, Oxygen and Beryllium).
- The outer layers of the star expand and cool.
What happens to form a White Dwarf star?
- When a red giant has used up all its fuel, fusion stops and the core contracts as gravity is now greater than the outward force.
- The core becomes very dense.
- A white dwarf will eventually cool to a black dwarf.