Measuring Distance In Space
Produced by the American Museum of Natural History, January 2006.
This interactive explains how astronomers measure the properties of light from faraway space objects to calculate their distance from Earth. Users click through a series of pages that explain the concepts step-by-step with illustrations and animations.
Interactive begins here
Visual: An animation of the expanding Universe. Galaxies arranged in a cluster gradually move farther away from each other.
As the Universe expands, objects farther from us are receding faster.
Page 2-Motion Changes Light
Visual: An animation of a star moving closer to and farther away from Earth. As it moves closer, it turns blue. As it moves farther, it turns red. In the corner, a dot follows the starís color changes along a rainbow-striped spectrum.
The light that a space object emits changes color depending on its speed and whether it is moving toward or away from us. Light from objects approaching us shifts toward the blue end of the spectrum. Light from objects moving away from us shifts toward the red, a phenomenon called ìredshift.î
Page 3-How Does Motion Change Light?
Visual: A light bulb sits between two eyes, as if two people were looking at the bulb. A wave form connects the two eyes and bulb. As the bulb shifts back and forth between the eyes, the wave form stretches and shrinks. The wavelengths get skinnier when it is moving towards an eye, and wider when it moves away from an eye.
Redshift in light waves is comparable to the Doppler effect for sound waves, which causes the siren on a police car moving away from you to have a lower pitch than a siren approaching you. For light, ìlower pitchî corresponds to a ìredderî color.
Page 4-Color Conveys Distance
Visual: Two galaxies are positioned in space far from Earth. One is nearer to Earth than the other. Arrows indicate they are moving away from Earth.
The farther away an object is, the faster itís moving. Therefore, its light is more redshifted. Scientists calculate a galaxyís distance by detecting its redshift.
Page 5-Try It!
Visual: Four animated boxes are on the page. In first box, a galaxy moves closer and farther from Earth. The user can manipulate sliders in three other boxes (which represent distance, velocity, and color spectrum) to see how the four variables are related. (Distance, velocity, and red shift all increase with a galaxyís distance to Earth.)
Drag the galaxy, distance, velocity, or color spectrum to see how they are related.
Page 5-What Is Wavelength?
Visual: Selected colors of the rainbow rise in columns on a graph. Eventually, they form an entire rainbow spectrum in a ìmountainousî shape on the graph. The highest peak is in the green color. Nearby, a photograph shows a green point of light among a number of other colored spots of light in the night sky.
Light is composed of different wavelengths, which the eye registers as different colors. A spectrum is the range of wavelengths emitted by a luminous object. The spectrum on the graph belongs to the quasar J162116.92-004250 in the photograph. It glows green because that is the wavelength of light it emits most. If this quasar were more distant, its spectrum (including its peak color) would shift toward the red.
Interactive ends here