Leonid Meteor Shower a Good Show
Observers have noticed how early darkness now falls in the evenings than just a few weeks ago. The temperature is still warm enough to go out after dinner with the binoculars or scope to take in some moongazing or stargazing well before bedtime.
November is the month that stargazers look forward to observing the Leonid meteor shower. The last few years this shower has been relatively weak but in the past the Leonids have put on a spectacular show of meteors. The most recent notable displays were in the years 1999 to 2002. I found that the best recent display was on November 17, 2001 with up to 900 meteors per hour along with some brilliant fireballs mixed in. The most memorable Leonid event I remember was pre-dawn on November 17, 1966 (40 years ago) when my estimates on the meteor rates at peak were 5-6 per second (20,000 per hour). The waxing crescent moon had already set leaving a fairly dark sky from my location. Even with the few clouds at the time there was plenty of clear dark sky to observe this spectacular event. I refer to it as a “Leonid meteor storm” rather than just a “meteor shower”.
Meteoroids come from comets as they move around the sun. As the comet approaches the sun it is warmed and sheds dust and debris along its orbital path. The Earth crosses this trail of material and its gravity sweeps it up. The Earth moves through space at a high speed – around 100,000 km/hr (28 km/sec). The debris shed by the comet moves through space at speeds from 10 to 60 km/sec. These speeds are maintained as there is nothing in space to slow the meteoroids. When the Earth runs into this space dust the dust particles enter the upper atmosphere. The atmosphere contains matter in the form of gases which are compressed in front of the fast moving particle. This compression (not friction) generates enough energy to heat the surface of the meteoroid white hot (around 1700 degrees C) and vapourize it. This high surface temperature breaks down the molecules of the meteoroid material and the air that it is passing through into glowing ionized particles. These particles recombine, release light energy and form the recognizable bright streak left by the meteor. Meteors are meteoroids as they “streak” through the atmosphere. Meteorites are the material that survive the passage through the atmosphere and make it to the earth. Most meteoroids are the size of a grain of sand and burn up in the atmosphere creating a meteor trail a meter wide, but because of its high speed, are generally many kilometers long.
The meteors from the Leonids originate from the periodic comet 55P/Tempel-Tuttle. Every 33 years this comet passes through the inner solar system shedding debris along its orbit adding material to the general meteoroid stream. The Earth will pass through this stream on the night of November 18-19. The meteors, coming from a point in space called the radiant, will appear to radiate from a point in the head of the lion of the constellation Leo (hence the name “Leonid meteor shower”). The best time to spot the meteors will be after midnight from a dark location away from city lights. The meteors will be seen anywhere in the dark sky but a general north-easterly direction will increase your chances of spotting a meteor. The moon is almost new so its light will not wash out any of the faint meteors. At the peak experts estimate 100 meteors per hour. I am not quite that optimistic. As I mentioned last month meteor observing is not a vigorous activity so dress warm to be comfortable for the duration of your observing session.
The only bright planet high in the night sky this month is Saturn. By mid-November it rises around midnight and is well up before dawn. Saturn is still bright but not as bright as in past years. This is due to the fact that the rings are closing therefore reflecting less sunlight. Use a telescope to see the planet cast its shadow onto the rings. Look for the last quarter moon near Saturn and the star Regulus (in Leo) on the night of November 12.
Clear Skies
Ted Bronson