November 17
The First Telescopic Double
Sun Position
The Sun is in Scorpius near -22° declination. Northern Hemisphere is approaching its seasonal mid-point between autumnal equinox and winter solstice. Southern Hemisphere summer is underway.
Sky Highlight
The Leonid meteor shower peaks around November 17–18, producing its fastest meteors of any annual shower, about 71 km/s. Even in ordinary years, a dark-sky observer can count 15–20 per hour at peak from the Northern Hemisphere. In exceptional years near the comet's return, outbursts of thousands per hour have been recorded. The radiant is in Leo, best placed before dawn.
Deep Sky Object
M1, the Crab Nebula, supernova remnant in Taurus, about 6,500 light-years away. With the Leonid radiant in the east and Taurus well up, M1 is conveniently placed tonight. The expanding shell is still 1,500 years removed from its visible edge; the pulsar at its center has been slowing by a measurable fraction every year since the explosion.
Featured Star
Mesarthim (γ Arietis) is a matched pair of blue-white main-sequence stars 164 light-years away (B9V + A1V). In 1664, Robert Hooke accidentally discovered it as one of the first double stars ever resolved through a telescope. The two nearly equal components, separated by a few arcseconds, are still a satisfying telescopic split today.
Around This Date
- November 17, 1970Lunokhod 1 began surface operations after being deployed from Luna 17, becoming the first remote-controlled rover to operate on the Moon.
- November 17, 1869The Suez Canal opened, an event widely observed and celebrated; the canal's construction relied in part on surveying methods derived from astronomical triangulation.
Mesarthim looks like one star, holds two, a small discovery that opened an entire branch of observational astronomy.