Changes

In 1887, for the first time photographs were taken of the galaxy, revealing its spiral shape. In 1912 the "nebula" was measured by the [[Lowell Observatory]] at moving at a radial velocity of 300&nbsp;km/s towards the Earth.<ref>http://www.seds.org/messier/m/m031.html</ref>

In 1887, for the first time photographs were taken of the galaxy, revealing its spiral shape. In 1912 the "nebula" was measured by the [[Lowell Observatory]] at moving at a radial velocity of 300&nbsp;km/s towards the Earth.<ref>http://www.seds.org/messier/m/m031.html</ref>

The first person to discover the true distance and nature of Andromeda was [[Heber Curtis]], when in 1917 he examined several previous photographs of the galaxy, finding 11 more novae, noting that they were 10 magnitudes fainter then similar novae in our own galaxy.  Because of this, he became a proponent of the "island universes" hypothesis, estimating Andromeda to be 500,000 light years distant, and as a separate galaxy.  The debate to whether Andromeda was another galaxy (and indeed if there were other galaxies) was conclusively settled when in 1923, when [[Edward Hubble]] discovered the first extragalactic [[Cepheid variable]]s, located within Andromeda, showing that it was not a nebulae within the [[Milky Way]], but another distant galaxy.<ref>http://adsabs.harvard.edu/abs/1929ApJ....69..103H</ref>   

The first person to discover the true distance and nature of Andromeda was [[Heber Curtis]], when in 1917 he examined several previous photographs of the galaxy, finding 11 more novae, noting that they were 10 magnitudes fainter then similar novae in our own galaxy.  Because of this, he became a proponent of the "island universes" hypothesis, estimating Andromeda to be 500,000 light years distant, and as a separate galaxy.  The debate to whether Andromeda was another galaxy (and indeed if there were other galaxies) was conclusively settled when in 1923, when [[Edwin Hubble]] discovered the first extragalactic [[Cepheid variable]]s, located within Andromeda, showing that it was not a nebulae within the [[Milky Way]], but another distant galaxy.<ref>http://adsabs.harvard.edu/abs/1929ApJ....69..103H</ref>   

The distance to the galaxy was again doubled when in 1953 when a second dimmer type of Cepheid variable was discovered.  This distance was further refined in the 1990s using the [[Hipparcos]] satellite to calibrate Cepheid distances using [[red giant]]s and red clump stars.<ref>http://arxiv.org/abs/astro-ph/?9802121</ref>

The distance to the galaxy was again doubled when in 1953 when a second dimmer type of Cepheid variable was discovered.  This distance was further refined in the 1990s using the [[Hipparcos]] satellite to calibrate Cepheid distances using [[red giant]]s and red clump stars.<ref>http://arxiv.org/abs/astro-ph/?9802121</ref>

[[Category:Astronomy]]

[[Category:Astronomy]]