What Is Redshift in Astronomy?
Redshift is the phenomenon where light from an object moving away from an observer is stretched, increasing its wavelength and shifting it toward the red end of the electromagnetic spectrum. It is a key piece of evidence for the expansion of the universe and a crucial tool for measuring cosmic distances.
Section 2: The Doppler Effect and Light
Redshift is a manifestation of the Doppler effect, which applies to all waves, including sound and light. Just as the pitch of a siren's sound lowers as it moves away from you (its sound waves stretch), the frequency of light waves decreases as the light source moves away. This decrease in frequency corresponds to an increase in wavelength, causing the light to appear redder.
Section 3: A Practical Example
Imagine a distant galaxy. By analyzing the light it emits using a technique called spectroscopy, astronomers can identify the unique spectral lines of elements like hydrogen. If the galaxy is moving away from Earth, these known spectral lines will appear at longer wavelengths than they would in a laboratory. This observed shift toward the red part of the spectrum is its redshift.
Section 4: Why Is Redshift Important?
Redshift is fundamentally important in astronomy. It provides the primary evidence that the universe is expanding, as nearly all distant galaxies show a redshift. Furthermore, the amount of redshift is proportional to the galaxy's distance and its speed of recession. This relationship, known as Hubble's Law, allows astronomers to map the universe and estimate its age.