October 13

October 13

The Quadruple Disguise

Sun Position

The Sun is in Libra near -9.5° declination. Days in the Northern Hemisphere mid-latitudes are now about one and a half hours shorter than at the equinox; southern days have gained the same margin.

Sky Highlight

October is the prime month for the Andromeda Galaxy at its highest evening elevation for Northern Hemisphere observers. The galaxy's full angular extent (about three degrees across for the visible core) is best appreciated with binoculars or the naked eye under dark skies, not a telescope, which magnifies individual patches but loses the whole.

Deep Sky Object

M32, an elliptical dwarf galaxy about 2.5 million light-years away. M32 is a compact elliptical galaxy that orbits M31 as a satellite, and it is one of the densest galaxies known, its stars are packed so tightly that some astronomers think it may be the stripped core of a once-larger spiral consumed by Andromeda long ago. Shares visibility with M31; best from Northern Hemisphere in October, visible but low from southern mid-latitudes.

Featured Star

Almach (γ And) is one of the finest color-contrast double stars in the sky: an orange giant (K3IIb) paired with a blue main-sequence companion (B9.5V) about 355 light-years away. The color contrast is vivid in small telescopes. What looks like two stars is actually at least four, the blue companion is itself a spectroscopic triple system. Almach, orange and blue at Andromeda's foot, a quadruple star disguised.

Around This Date

  • October 13, 1773Charles Messier observed M74, a face-on spiral galaxy in Pisces, adding it to his catalog, it remains one of the most challenging Messier objects to see visually due to its very low surface brightness.
  • October 15, 1997NASA and ESA launched the Cassini-Huygens spacecraft toward Saturn, beginning a seven-year journey that would produce the most detailed study of the Saturn system ever conducted.

The best things to look for in Almach (the color contrast, the multiplicity) require a telescope, which is a good reason to bring one out in October.