2017 November 15
Observer’s Challenge – The Leonid meteor shower
The Leonids attracted great interest in the late 1990s because astronomers were predicting large numbers of meteors during the nights of peak activity, giving observers the opportunity to see meteor storms as previously reported and photographed in 1966, and wonderfully described in 1833 when “the stars fell like rain”. The predictions met our expectations of highly intensive but short-lived bursts of meteor activity, and from 1998 to 2002 observers around the world were treated to spectacular displays of Leonid meteors, from rich showers of faint meteors to bright fireballs.
The parent body of the Leonid meteors is comet 55P / Tempel-Tuttle with a period of 33.2 years. As it orbits the Sun the comet distributes streams of dust particles in its wake. If the Earth encounters one of these streams it produces a meteor shower when the cometary debris is vaporised in the upper atmosphere, explaining the intensity of Leonid meteor storms observed near the comet’s perihelion passage.
Leonid meteors (radiating from the constellation of Leo) can be seen throughout November, although most are visible between the 15th and 20th, with peak activity expected on the night of the 17th. We are a few years away from the return of their parent comet so they exhibit low rates, giving a ZHR (Zenithal Hourly Rate) of about 10 at maximum under clear dark skies. This is not expected to increase significantly until the late 2020s, although the Earth encounters varying streams of Leonid meteoroids, so there’s always a chance to see a nice meteor display.
The Leonids are the Usain Bolts of the meteor family. They are fast, following their parent comet’s retrograde orbit inclined at 162o to the ecliptic, they slam into the Earth’s atmosphere with geocentric velocities of 70 km/s, 160,000 mph! Leonid meteors are usually visible for less than a second as they zip across the sky. Bright ones often leave a glowing train.
Video networks are monitoring this year’s return of the Leonids and observers are encouraged to undertake visual watches, either individually or in groups. Conditions are very favourable with maximum occurring this weekend during New Moon. The radiant rises late in the evening, so watches after midnight will be the most productive.
A DSLR can also be used to record meteors. A series of 30s exposures with a fast f/ratio standard or wide-angle lens is recommended; the ISO setting will depend on local sky conditions.
Alex has been a BAA member for many years. His main interest is video astronomy, applying video techniques to record transitory phenomena such as asteroidal and lunar occultations, meteor showers, and performing video astrometry of asteroids, Near Earth Objects and comets. He is co-founder of NEMETODE, a network of video meteor cameras in the British Isles.