October 31, 2014

See the Orionid Meteor Shower at its Peak.

The Orionid radiant. (Credit: Stellarium).

The Orionid radiant. (Credit: Stellarium).

Meteor season is now well underway. About midway between the August Perseids and the November Leonids is an often over-looked shower; the Orionids. The good news this year is the Orionids occur around the morning of October 21st, when the light-polluting moon is only three days past new and thus safely out of the morning sky. Expect to see up to 20-30 fast moving meteors, as was generally the reported case last year. For best results, be sure to watch several hours before dawn, or about 2-5 PM local. The radiant lies just above and to the left of Alpha Orionis also known as the red giant star Betelgeuse. The Orionids are also known for a perceived exceptional number of fireballs and bolides which are said to exhibit a yellowish or green color. And the progenitor comet? None other than the most well known of them all; comet Halley! Its nice to know that even though Halley’s next apparition isn’t until 2061, we can still enjoy its annual trail of debris pelleting our atmosphere!

The astro-term of the week is the Poynting-Robertson effect. A real vocabulary builder to be sure! Initially posited by John Henry Poynting in 1903, this is the drag created by radiative pressure on an orbiting mass by solar energy causing it to lose momentum and slowly spiral inward towards the sun. In Poynting’s time, this was considered to be an effect of the drag caused by the “stellar ether” a substance thought to permeate space and propagate gravity and light. Einsteins theory of relativity did away we the need for ether, and in 1937 Howard Robertson correctly explained the effect in terms of general relativity. The effect is greater on smaller, dust grained-sized bodies, and modeling of meteor streams such as the Orionids have to take into account the Poynting-Robertson effect for accurate predictions. So, if you went to the local Halloween party as the Doppler effect last year and found it to be less than original, why not design a costume for the Poynting-Robertson effect this year in a keen sense of one-up-man-ship?

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