Milky Way, the Universe, Galaxies and the development of theories

Mon, 05 May 2008 02:17:02 GMT

clipped by: ruralart
clipper's remarks: A bit on the history of discovery of galaxies and the Milky Way... rather interesting to see how it has evolved.

Clip Source: ircamera.as.arizona.edu

Discovery of Galaxies

Key points: How it was established that other galaxies are island universes of stars; standard candles and distances; the distance ladder

While the Milky Way was considered to be a thin, distorted disk of stars with the sun near the center in the early 20th century, other galaxies were confused with gaseous nebulae, and were assumed to be part of Milky Way.

The best pictures showed other galaxies to have spiral arms, but they also appeared smooth and were thought to be a special kind of gaseous nebulae, the "spiral nebulae".

By the 1920s, a debate was ranging among astronomers about whether the spiral nebulae were gaseous objects (HII regions) or separate "island universes" like the Milky Way. Vesto Slipher had obtained spectra that showed them to have continuous spectra, not emission lines, consistent with their being made of stars.

More on the debate at http://antwrp.gsfc.nasa.gov/diamond_jubilee/debate_1920.html

Tags: astronomy, galaxies, milky way, history, science, space

Losing the Dark

Sun, 04 May 2008 22:35:56 GMT

clipped by: ruralart
clipper's remarks: Maps showing the loss of dark over the last 50 years or so.

Clip Source: www.yosemite.org

Growth of Light Pollution in North America

The maps show artificial night sky brightness and are based on upward light measured by the Defense Meteorological Satellite Program after accounting for propagation and scattering of that light in the atmosphere.

The night sky in all areas here which are not black (but have other colors) is considered polluted. Today, two thirds of the USA's population have lost naked eye visibility of the Milky Way.

The colors indicate the artificial night sky brightness as a fraction of the average natural night sky brightness.

Tags: astronomy, night, dark, sky, lights

Clipmarks | ruralart's clips

Milky Way, the Universe, Galaxies and the development of theories

Losing the Dark