P7 Page 8 Flashcards
What is the definition of the parallax angle?
The parallax angle is half the angle moved against distant background stars over 6 months. The nearer the objects to you the greater the anlge.
What is Parallax?
Parallax is an apparent change in position of an object against a distant background. It makes closer stars appear to move relative to distant ones over a course of a year.
What is the parallax angle usually measured in?
Arcseconds
1 arcsecond=
=1”=( 1 )
–––––
3600
The smaller the parallax angle, the further or closer the star?
The further away.
Distance(pc)=
1
=(–––––––––––––)
Angle(arcsec)
What is luminosity or intrinsic brightness?
How bright the star would seem if you were right next to it.
What does a stars luminosity depend on?
It’s size and temperature. The bigger and hotter it is, the more energy it gives out, so the brighter it is.
Why does a star seem dimmer the further away you are from it?
Because less of its energy is reaching you.
What does the observed intensity or observed brightness of a star depend on?
It’s luminosity and how far away it is from you.
What are Cepheid variables?
They are stars that pulse in brightness, they get brighter and then dimmer over a period of days.
How are the Cepheid variables luminosity linked to their pulse rate?
The greater the luminosity, the longer time between pulses(pulse period)
How can astronomers work out the distance of Cepheid variables?
By comparing their luminosity and observed brightness of a star.
