Space (10) Flashcards
(57 cards)
What happens to light as it leaves the surface of a star?
It spreads out uniformly through a spherical shell.
What is the formula for the surface area of a sphere?
4πr^2.
What do the symbols in the inverse square law represent
F=radiant flux
L=luminosity
d=distance from star
What assumptions does the inverse square law equation make?
1) The star radiates power uniformly through space
2)No radiation is absorbed between the star and Earth
What does the inverse square law tell us about luminosity?
The luminosity L of a star is constant regardless of distance.
What is the principle of parallax based on?
It is based on how the position of an object appears to change as the position of the observer changes.
What is stellar parallax used for?
It is used to measure the distance to nearby stars.
Define stellar parallax.
The apparent shifting in position of a nearby star against a background of distant stars when viewed from different positions of the Earth during its orbit around the Sun.
Why do nearby stars appear to shift in position over time?
Because the Earth changes position as it orbits the Sun, causing closer stars to appear to move relative to distant stars.
Why do distant stars not appear to move?
Because they are much farther away, making their apparent motion negligible.
What is the relationship used to calculate stellar parallax?
tan(p)=AU/d , where AU is the radius of Earth’s orbit, p is the parallax angle, and d is the distance to the star.
When are stellar parallax observations typically made?
In January and again in July, six months apart, to maximize the distance the Earth has moved.
What simplification is used for small angles in stellar parallax calculations?
tan(p)=p, so the equation simplifies to p=AU/d
What is the equation for measuring stellar distances in parsecs?
p=1/d
(p is parallax angle in arc-seconds, and d is the distance in parsecs
Why is stellar parallax only accurate for distances up to 100 parsecs?
Because for distances larger than 100 parsecs, the angles involved become so small that they are difficult to measure accurately.
What is a standard candle
A stellar object with known luminosity
Give two examples of standard candles
Cepheid variable stars and Type 1a supernovae
How do Cepheid variable stars act as standard candles
Their brightness varies over a set period, and this variation has a well-defined relationship with their luminosity
Why are Type 1a supernovae useful as standard candles?
The luminosity at the time of the explosion is always the same, making them reliable distance indicators
Why is measuring astronomical distances challenging
A direct measurement is only possible for objects close to Earth, requiring indirect methods for distant objects
How do standard candles help measure distances
If the luminosity is known, the distance can be estimated based on how bright the object appears from Earth
What is the cosmic distance ladder
A method where different distance measurement techniques are combined to determine the scale of the universe
What are the axes on the Hertzsprung-Russell diagram?
Y-axis: Luminosity (dim at the bottom, bright at the top); X-axis: Temperature (hot on the left, cool on the right).
What did Hertzsprung and Russell discover about stars?
Stars cluster in distinct areas on the diagram, with most forming a band called the main sequence.
