# Physics 7.3 (Astronomy)

HideShow resource information
• Created by: Becca.
• Created on: 23-06-16 08:40

## Measuring Distance to Stars

Parallax method The apparent movement of close stars against the background of stars

When d = 1 parsec ; p = one second

However: beyond 300 parsecs the angle is too small to measure and so can't measure the distance to most stars

Brightness method Further away stars appear dimmer but this assumes all stars have the same luminosity (temperature and size)

Cepheid variable stars are stars which vary in brightness those with higher luminosity have longer periods. They can  be used in the brightness method by comparing stars with the same apparent brightness to the luminosity.

1 of 3

## Curtis vs Shapley

Curtis Milky way is one of many galaxies (spiral nebulae = other galaxies)our galaxy is only 10 000 parsecs across with our sun close to the centre of the universe

Shapley Universe is one large galaxy (spiral nebulae = gas clouds) about 100 000 parsecs across with our sun and solar system far from the centre of the galaxy

Hubble Helped to solve Curtis/Shapley debate by proving objects were outside of our galaxy. Distant galaxies are moving away from us (further the galaxy the faster the movement) as shown by red shiftSuggests the universe began from one point which supports the Big Bang theory

2 of 3

## Hubble's law

Hubble's law Recessional velocity = red shift Gradient = age of universe (estimate)

VHor

Velocity of galaxy Hubble's constant Distance to galaxy

1 / H= estimate for the age of the universe

Ho  2*10-18

3 of 3