Astronomical Distances and Brightness

Question 1

What is Parallax?

Answer 1

The apparent change in position of an object against a distant background. It makes closer stars appear to move relative to distant ones over the course of a year

Question 2

What is the parallax angle?

Answer 2

It is half the angle moved against distant background stars over 6 months (at the opposite ends of the Earth’s orbit). The nearer an object is to you, the greater the angle

Question 3

What is the parallax angle measured in?

Answer 3

Arcseconds (rather than degrees)

Question 4

What is parallax used for?

Answer 4

To calculate the distance to nearby stars; the smaller the parallax angle, the more distant the star is.

Question 5

What is a parsec (pc)?

Answer 5

The distance to a star with a parallax angle of 1 arcsecond

Question 6

How many light years are equivalent to 1 parsec?

Answer 6

3 light years

Question 7

What is the formula to work out the distance to a star in parsecs?

Answer 7

distance (pc) = 1 / angle (arcsec)

Question 8

What does a star’s observed intensity depend on?

Answer 8

The distance of the star

Its luminosity

Question 9

What are Cepheid Variable Stars?

Answer 9

Stars that pulse in birghtness over a period of several days

Question 10

What does the rate at which Cepheid Variable stars pulse depend on?

Answer 10

Their luminosity; the greater the luminosity, the longer time between their pulse period

Question 11

How do astronomers work out the distance to a Cepheid star?

Answer 11

By comparing the luminosity (worked out from pulse period) and the observed brightness of the star