Tonight and tomorrow night – October 20 and 21, 2015 – present the probable best nights of the annual Orionid meteor shower. And an awesome shower it is! Debris in the orbit of a comet – the Orionid meteor stream – is now encountering Earth’s atmosphere. The meteors will become visible, starting at late evening on October 20, and usually put on their greatest display in the dark hours before dawn on October 21 and 22. At the peak, from a dark site, you might expect to see about 10 to 20 meteors per hour.
What’s more, the Orionids stem from debris from the most famous of all comets, Comet Halley, pictured at the top of this page. The picture shows Comet Halley itself at its 1910 visit. The comet last visited Earth in 1986 and will return next in 2061.
The meteors – vaporizing bits of comet ice and dust – will look like streaks of light in the night sky. They’re sometimes called shooting stars.
As is standard for most meteor showers, the best time to watch this shower will be between the hours of midnight and dawn – regardless of your time zone.
Fortunately, in 2015, the first quarter moon sets in the late evening or near midnight on October 20, leaving the morning hours dark for meteor watching. Also, in the predawn and dawn sky, look for Sirius, the sky’s brightest star. And the planets Venus and Jupiter are also very bright – brighter than Sirius – and visible in the sky before dawn.
As Comet Halley moves through space, it leaves debris in its wake that strikes Earth’s atmosphere most fully around October 20-22, every year. The comet is nowhere near, but, around this time every year, Earth is more or less intersecting the comet’s orbit.
If the meteors originate from Comet Halley, why are they called the Orionids? The answer is that meteors in annual showers are named for the point in our sky from which they appear to radiate. The radiant point for the Orionids is in the direction of the constellation Orion the Hunter. Hence the name Orionids.
Even one meteor can be a thrill. Bring along a blanket or lawn chair – after midnight or before dawn – and lie back comfortably while gazing upward. Although a somewhat modest shower, these swift-moving meteors are sometimes bright, occasionally leaving a persistent train – a glowing streak that lingers momentarily after the meteor has gone!
Bottom line: Best nights for the Orionid meteor shower in 2015 are October 20-21 and 21-22, especially between midnight and dawn. You might see as many as 15 to 20 meteors per hour from a dark site.