Planets of the Solar System: Tilts and Spins

How does your favorite planet spin? Does it spin rapidly around a nearly vertical axis, or horizontally, or backwards? The featured video animates NASA images of all eight planets in our Solar System to show them spinning side-by-side for an easy comparison. In the time-lapse video, a day on Earth — one Earth rotation — takes just a few seconds. Jupiter rotates the fastest, while Venus spins not only the … Read More →

A Circumhorizontal Arc Over Ohio

Why would clouds appear to be different colors? The reason here is that ice crystals in distant cirrus clouds are acting like little floating prisms. Sometimes known as a fire rainbow for its flame-like appearance, a circumhorizon arc lies parallel to the horizon. For a circumhorizontal arc to be visible, the Sun must be at least 58 degrees high in a sky where cirrus clouds are present. Furthermore, the numerous, … Read More →

Anemic Spiral NGC 4921 from Hubble

How far away is spiral galaxy NGC 4921? It’s surpringly important to know. Although presently estimated to be about 300 million light years distant, a more precise determination could be coupled with its known recession speed to help humanity better calibrate the expansion rate of the entire visible universe. Toward this goal, several images were taken by the Hubble Space Telescope in order to help identify key stellar distance markers … Read More →

Young Star Cluster Trumpler 14 from Hubble

Why does star cluster Trumpler 14 have so many bright stars? Because it is so young. Many cluster stars have formed only in the past 5 million years and are so hot they emit detectable X-rays. In older star clusters, most stars this young have already died — typically exploding in a supernova — leaving behind stars that are fainter and redder. Trumpler 14 spans about 40 light years and … Read More →