September 27
The Chained One Rises
Sun Position
The Sun is in Libra at about -3° declination, moving south at roughly 24 arcminutes per day. Northern Hemisphere mornings are noticeably darker; Southern Hemisphere dawn is arriving earlier.
Sky Highlight
The Andromeda Galaxy (M31) is now at its best seasonal position for Northern Hemisphere observers, nearly overhead by late evening at latitudes around 40°N. A dark sky away from city lights makes it the largest and most distant object visible to the naked eye, a faint oval three times the Moon's width.
Deep Sky Object
M31, Andromeda Galaxy, plus companion M110. At about 2.5 million light-years, M31 appears 3° across in its full extent; M110 (NGC 205) is a dwarf elliptical companion visible in binoculars just northwest of the nucleus. For Northern Hemisphere observers, this is prime season; for southern mid-latitudes, M31 is low in the north.
Featured Star
Alpheratz (α And), the chemically peculiar blue subgiant at 97 light-years with spectral type B8IVpMnHg, stands at the northeast corner of the Great Square and simultaneously begins the chain of stars that defines Andromeda. Tonight, with M31 prominent in the northeast, the connection between the myth's named star and its galaxy namesake is easy to trace.
Around This Date
- September 27, 1905Albert Einstein submitted his paper on special relativity's mass-energy relationship, which would later be published as the fourth of his 1905 Annus Mirabilis papers, introducing E=mc².
- September 28, 2015NASA announced evidence for briny liquid water moving seasonally on the Martian surface, based on spectroscopic identification of hydrated salts in recurring slope lineae features.
Alpheratz leads you into Andromeda's chain and from there to a galaxy, a route across 2.5 million light-years that begins with a single named point.