May 9
The Retired Pole Star
Sun Position
The Sun is in Taurus at roughly +17.6° declination. Northern afternoons are warm and the Sun climbs higher at noon than at any point since late summer. Southern evenings carry the first real chill of autumn.
Sky Highlight
May 9 marks the calendar anniversary of the Transit of Venus of 1761 and 1769, the pair of rare events that gave astronomers their first precise measurement of the Earth-Sun distance. Transits of Venus come in pairs separated by 8 years, with gaps of more than a century between pairs; the next transit after 2012 will not occur until 2117.
Deep Sky Object
M102 (NGC 5866), lenticular galaxy in Draco, about 50 million light-years away, seen nearly edge-on with a sharp central dust lane. Its identity has been debated, some catalogs list it as the Spindle Galaxy, though that name also belongs to NGC 3115, but the object itself is striking and unambiguous in a telescope. Best from northern latitudes.
Featured Star
Thuban (α Draconis) is a white giant 303 light-years distant, spectral class A0III. Due to Earth's axial precession, Thuban served as the North Pole Star around 2700 BCE, making it the pole star of ancient Egypt when the Great Pyramid was built. It has since been displaced by Polaris, and the pole will not return to Thuban for roughly 21,000 years.
Around This Date
- May 9, 1761Astronomers across the world observed the Transit of Venus across the Sun's disk, part of an international campaign to measure the solar parallax and determine the Earth-Sun distance for the first time.
- May 9, 1994The Hubble Space Telescope observed Comet Shoemaker-Levy 9 in detail before its collision with Jupiter, providing scientists with a close look at the fragmented comet chain.
The old pole stars don't disappear, they just go back to being ordinary.