Sloan Digital Sky Survey (3D Map)
From 2000 a 2.5-metre telescope in New Mexico with a 30-chip digital camera mapped the sky in colour and 3D, and its galaxy map revealed a ruler of about 500 million light-years left by the early universe.
Open in the interactive tree →The Sloan Digital Sky Survey began collecting data in 2000 with a dedicated telescope at Apache Point, a camera of 30 CCD chips (about 120 megapixels) and a spectrograph that recorded 640 spectra at once; it has imaged nearly a billion objects, taken spectra of more than 4 million, and put its data online. In 2005 the team found, among 46,748 luminous red galaxies, a faint preferred separation of roughly 500 million light-years: the frozen echo of sound waves in the early universe, which also shows up in the cosmic microwave background. This ruler lets astronomers trace how fast space expanded, and the DESI survey used the same method to report in 2024-2025 that dark energy may be weakening.
Prerequisites
- Expansion & Big Bang1929Redshifts of galaxies measure cosmic expansion
- Cosmic Microwave Background1964The early sound waves it measures are also imprinted in the microwave background
- CCD Image Sensor1969A camera of 30 CCD chips images the sky
Unlocks
- DESI Survey: Is Dark Energy Changing?2025DESI repeats and extends the baryon acoustic oscillation measurement first made with SDSS