Документ взят из кэша поисковой машины. Адрес оригинального документа : http://zebu.uoregon.edu/messier/m57.txt Дата изменения: Thu Apr 28 20:48:10 1994 Дата индексирования: Mon Oct 1 21:28:59 2012 Кодировка: Поисковые слова: astro-ph

M57 is another famous and often photographed object. It is
also known as the Ring Nebula. Its angular size is only about
one arcminute meaning its an excellent target for long focal
length systems. As M57 is overhead in the summer for US
observers, almost every amateur with a telescope has seen it.

The object itself is known as a Plantary Nebula because, in
a small telescope, these objects exhibit the same appearance
as a resolved planetary disk. Of course, they have nothing to
do with planets but rather represent late stages in the evolution
of low mass stars in which a double shell source (Hydrogen and
Helium Burning) around a non-fusing Carbon core is driving the
outer layes of the star away, thus revealing a hotter star (the
central star of the Planetary nebula). This hotter core then
emits enough UV radiation to ionize what used to be the outer
layers of the star.

Here we present 3 images:

1. Normal black and white image

2. Color astroCCDing with Nelson Caldwell - notice how blue the
Central Star appears here.

3. A long exposure CCD image, obtained by George Jacoby of Kitt Peak,
that saturates the interior but shows the faint, outer, filamentary
structure.