Parallax
Parallax * Parallax is the apparent movement of a nearby object when it’s viewed from 2 different points. * The farther the star the smaller the angle * Distance from one side of earth orbit to other is 300km. * distance from earth to sun is 1 AU * Can only measure close stars reliably. * Parallax is very small due to distance to stars. Makes it harder to measure accurately. * Relies on no assumptions, only earth’s geometry around the sun. * Uses simple trigonometry to calculate distances.
Method: observe a close star within 100 ly, through a telescope. Observe its position and record its position as well as the background stars positions. in 6 months observe and record the same star’s position.
Radar * Based on fact light travels at 300,000 km/s. * Radio waves, microwaves, x-rays or visible light * Basic formula 2d = vt, d=distance / v=velocity / t = time. * Measure time by sending waves and recording how long it takes to get back * Only nearby planets as waves spread out a lot on their journey and return * Also energy of reflection is small * Distances can be measured precisely * Can’t measure sun, no solid surface.
Method: Moon:
Send a laser to be reflected off reflectors left on the moon by moon mission astronauts.
Time the laser beam from sending it until you receive it. Planets:
Send a pulse of radar waves to the planet to bounce off the surface of the planet.
Measure the time from transmission to receiving the pulse of radar waves.
Cepheid * Stars which brighten and dim periodically. * Brighter the Cepheid the longer its period * Period is regular * relation between period and its absolute luminosity * period ranges from 1 – 100 days *
method: find the period to get the luminosity measure the apparent brightness determine distance from luminosity and brightness
RED SHIFT * Based on Edwin Hubble’s theory that the world
Method: observe a close star within 100 ly, through a telescope. Observe its position and record its position as well as the background stars positions. in 6 months observe and record the same star’s position.
Radar * Based on fact light travels at 300,000 km/s. * Radio waves, microwaves, x-rays or visible light * Basic formula 2d = vt, d=distance / v=velocity / t = time. * Measure time by sending waves and recording how long it takes to get back * Only nearby planets as waves spread out a lot on their journey and return * Also energy of reflection is small * Distances can be measured precisely * Can’t measure sun, no solid surface.
Method: Moon:
Send a laser to be reflected off reflectors left on the moon by moon mission astronauts.
Time the laser beam from sending it until you receive it. Planets:
Send a pulse of radar waves to the planet to bounce off the surface of the planet.
Measure the time from transmission to receiving the pulse of radar waves.
Cepheid * Stars which brighten and dim periodically. * Brighter the Cepheid the longer its period * Period is regular * relation between period and its absolute luminosity * period ranges from 1 – 100 days *
method: find the period to get the luminosity measure the apparent brightness determine distance from luminosity and brightness
RED SHIFT * Based on Edwin Hubble’s theory that the world