physics P1 (6)

The scale of the universe

• Moon has a 3500km diameter
• Earth has a 12500km diameter
• Solar system has a 12 billion km diameter
• Milky way galaxy has a 100000light years diameter
• Universe has a 59 billion light years diameter
• Astronomical distances are so huge that measurements of distance in kilometres are exceedingly large
• So the unit of distance used is the light year which is the distance travelled by light in one year
• Light travels at 300 000 000 m/s
• One light year = 9 460 000 000 000 000m

Red and blue shifts

• Light from moving objects will appear to have different wavelengths depending on the relative motion of the source and the observer
• Observers looking at an object that is moving away from them see light that has a longer wavelength that it had when it was emitted (a red shift), while observers looking at an approaching source see light that is shifted to shorter wavelength (a blue shift)
• By measuring the amount of shift to the red, we can determine the rate at which objects…