Stephan's Quintet
An astrophotographer's image of Stephan's Quintet shows one galaxy is a foreground interloper, while the others exhibit tidal interactions including a collision remnant and a stretched tidal plume. The image was captured over three nights with a C9.25 telescope.
Background
- **Stephan's Quintet** is a compact group of five galaxies in Pegasus, discovered in 1877. It's a famous example of interacting galaxies — gravitational forces between them create long "tidal tails" of stars and gas.
- **Redshift (z)** measures cosmic distance via the stretching of light. z=0.0026 ≈ 35 million light-years; z=0.022 ≈ 300 million light-years. The blue spiral (NGC 7320) is a foreground interloper, not part of the group.
- **NGC 7318** is a pair of colliding galaxies, not a single galaxy with two nuclei — an ongoing merger.
- **Hickson Compact Group 92** and **Arp 319** are catalog designations: the former for tight galaxy groups, the latter for Halton Arp's atlas of peculiar galaxies.
- The post is an amateur astrophotographer's report. Terms like C9.25 (telescope model), IMX533 (sensor), and asinh stretch (a non-linear image-processing technique) are equipment and processing details, not jargon requiring special background.