APOD: 2020 September 20 - Breaking Distant Light

Good morning, Rallypoint. Today's Astronomy Picture of the Day (APOD) is titled "Breaking Distant Light." Our featured image from the Visible MultiObject Spectrograph (VIMOS) operating at the Very Large Telescope (VLT) array in Chile takes light from distant galaxies and breaks it into its constituent colors (spectra). This allows astronomers to measure the redshift of known spectral lines and estimate how far away the galaxies are from Earth.

What is redshift? And what does it have to do with distance? Recall the Doppler effect, where the pitch of a sound seems to get lower and lower the further away its source is from your vantage point (think train whistle). Over cosmological distances, light behaves the same way. Based on the extent that spectral lines shift toward infrared (e.g. redshift), astronomers have a means to determine how far away a light source is based on a known formula.

So while many of the galactic spectral lines in today's APOD look similar, there are slight differences in each of them. This not only indicates how far each galaxy is from Earth, but also provides an idea of their predominant composition (e.g. hydrogen, nitrogen, oxygen, iron, etc). Analyzing the space distribution of distant objects will allow insight into when and how stars and galaxies formed, clustered, and evolved in the early universe.