October 21

October 21

Orionid Peak

Sun Position

The Sun is in Scorpius near -13.5° declination. Northern Hemisphere observers experience noticeably earlier sunsets; Southern Hemisphere observers are heading toward the long evenings of late spring.

Sky Highlight

The Orionid meteor shower peaks on or near October 21-22 each year, producing swift, bright meteors that can leave glowing trains. The shower is debris from Halley's Comet spread along Earth's orbital path; the meteors enter the atmosphere at roughly 66 km/s. The radiant is near the border of Orion and Gemini, highest after midnight. Both hemispheres see the shower; Northern Hemisphere observers get the radiant higher.

Deep Sky Object

M42 (Orion Nebula), an emission nebula and star-forming region about 1,350 light-years away. M42 is the nearest large star-forming region to Earth, where new stars are being born right now, the Trapezium cluster at its core contains four young, hot stars whose ultraviolet radiation is sculpting and illuminating the surrounding gas cloud into the forms visible in any backyard telescope. Visible from both hemispheres as Orion rises in the east; best in the Northern Hemisphere after midnight in autumn and in the Southern Hemisphere in late evening.

Featured Star

Achernar (α Eri) is a main-sequence B-type star (B6Vep) about 139 light-years away, rotating so fast it has ejected a disk of gas around its equator, the 'e' and 'p' in its spectral type indicate this emission and its polarization. It is the brightest star in the southern constellation Eridanus and the ninth-brightest star in the entire sky. Achernar, the river's end, a star too fast to be round.

Around This Date

  • October 21, 1923Edwin Hubble formally identified a Cepheid variable in the Andromeda Nebula from photographs taken that week, writing 'VAR!' on the plate and beginning the analysis that would resolve the Great Debate about extragalactic nebulae.
  • October 22, 1966The Soviet Luna 12 spacecraft entered lunar orbit and began transmitting photographs of the Moon's surface, contributing to site evaluation for future landers.

The Orionids are fast and brief. They are gone before you can point them out to anyone standing beside you.