Caldwell 4
The Iris Nebula was discovered by German-British astronomer Sir William Herschel on October 18, 1794. (Herschel has an impressive track record, having also discovered the planet Uranus and having been knighted in 1816.) His Iris Nebula has an apparent magnitude of 7. Located near the North Celestial Pole and the North Star (Polaris), Caldwell 4 is nearly impossible to see from the Southern Hemisphere. For best viewing in the Northern Hemisphere, use a telescope in early autumn to star hop from the two brightest stars in the constellation Cepheus. Since the Iris Nebula is faint and diffuse, dark skies away from city lights are recommended for viewing it.
This nebula is of particular interest to scientists because of its colors. Reflection nebulas glow because they are made up of extremely tiny particles of solid matter, up to 10 or even 100 times smaller than dust particles on Earth. These particles diffuse the light around them, giving the nebula a second-hand glow that’s typically bluish (like our sky). While the Iris Nebula appears predominantly blue, it includes large filaments of deep red, indicating the presence of an unknown chemical compound likely based on hydrocarbons. Studying nebulas like this one helps astronomers learn more about the ingredients that combine to make stars.
This close-up image, showing one rosy-colored region within Caldwell 4, is a composite of four exposures captured by Hubble’s Advanced Camera for Surveys in visible and near-infrared filters. Astronomers also studied the nebula with Hubble’s Near Infrared Camera and Multi-Object Spectrometer (NICMOS) to try to determine which chemical elements are present in Caldwell 4.
Credit: NASA & ESA
For more information, see:
www.spacetelescope.org/news/heic0915/
For Hubble's Caldwell catalog site and information on how to find these objects in the night sky, visit:
www.nasa.gov/content/goddard/hubble-s-caldwell-catalogWięcej informacji o licencji można znaleźć tutaj. Ostatnia aktualizacja: Mon, 22 Aug 2022 18:38:43 GMT