- by John Hlynialuk
Astronomy, just like any science has its share of confusing or misleading jargon. Take "Big Bang" for example. In 1927, Catholic priest Georges Lemaitre proposed the theory, calling it simply "an expanding model of the universe". That description never caught on. It was 22 years later when Sir Fred Hoyle referred to "this big bang idea" on a BBC radio show and the public latched onto "Big Bang" (in capitals). This phrase, however, is misleading because the Big Bang was neither a bang (no sound can carry in vacuum) nor very big since whatever was there in the beginning was very tiny indeed. It just expanded into bigness very quickly.
Another misleading term and one that everyone uses (including me) is "shooting star" for those bright streaks of light in the sky that do look like stars falling from heaven. Astronomers prefer "meteors" but the name has nothing to do with meteorology. The Greek word "meteoron" means "of the atmosphere" but the Greeks did not distinguish the lower 20 km or so, where weather occurs, from the far reaches at altitudes of several hundred km where bits of space debris burn up. One cannot blame them or other early astronomers for this lack of knowledge, of course.
To be clear then, "meteor" is the official name of the bright streak of light in the sky produced by particles usually no bigger than grains of sand or apple seeds. When they encounter even the thin upper atmospheres of planets, their tremendous speed causes them to be incinerated as they are forced to slow down. And yes, other planets like Mars and Saturn also have meteor showers.
Furthermore, in a "meteor shower" you will not get wet nor should you expect more than one or two meteors per minute, -this is not even a gentle sprinkle. However, on a few rare occasions in the past, meteors have been known to fall like rain (cue Bing Crosby singing "Stars Fell on Alabama"). That song commemorates one such display, a particularly intense burst of the Leonid meteors in Nov 1833. On that occasion, it was estimated that 100 000 meteors were seen per hour (that's 28 per second!) and probably 250 000 appeared in the sky during the 9-hour long event. Though Leonid "storms" recur ever 33 years or so, we do not expect a major display from the Leonids until 2031 or so. Don't worry, I will give you a heads-up well in advance.
Although early August is considered to be the best time of year for seeing meteors (the famous Perseids appear then), autumn is also good for shooting stars -this time minus the mosquitoes. In fact, the Geminid meteors around Dec 14 are rated better than the August Perseids in terms of numbers, 120 per hour as opposed to the Perseids' 90 per hour. The radiant of the Geminids, the point from which the meteors appear to stream, (think railway tracks converging in the distance), is also well placed in the sky and Gemini is visible from dusk to dawn. That shower is the best one of the year and if weather permits, well worth bundling up to observe for an hour or two (with breaks to warm up, of course).
In addition to the Geminids in December, there are two other meteor showers due this fall. The Orionids happen around Oct 21, -expect 20 meteors per hour once Orion is at its highest above the southern horizon. Orion rises around 11 pm in the east and if you are still watching at 4 am, expect close to the maximum number then.
Later in the year, on Nov 17, the peak of the famous Leonid meteors occurs but don't expect more than 20 meteors per hour this year. Look for the head of Leo to rise above the eastern horizon around 1 am and by 4 am, the full 20 per hour rate can be observed. The accompanying chart shows all three of the radiants of these fall meteor showers. They are all generally in the same part of the sky.
This year, all three also happen under better than average viewing conditions. The sky is not brightened by moonlight which can substantially reduce the number of meteors seen. Last August, the Perseids were affected by an almost full Moon, many faint meteors were washed out, and it was not a memorable display.
Join BAS members on Saturday Oct 21 at the Fox Observatory for some autumn meteor watching (weather permitting). There will be hot chocolate for everyone, of course!
Visit www.bluewaterastronomy.com for maps to the observatory and more information about these events.
