Published 9:07 PM EDT Oct 13, 2018
This feature has often discussed meteor showers around the time of their expected appearances.
In general, meteor showers are caused when comets – particularly those that return every few years – erupt dust grains off their nuclei as they make their respective passes through the inner solar system. These grains of dust never return to the comet, but instead continue on traveling around the sun in the same orbit as the comet.
Over time this dust spreads out all along the comet’s orbit. If the Earth, during the course of its annual trek around the sun, should encounter one of these streams of dust, we see the dust grains enter the atmosphere at speeds of up to several miles per second, and vaporize as streaks of light due to friction with the atmosphere.
A handful of such showers are quite strong and can produce as many as 60 or more meteors per hour, provided that the sky is not washed out due to bright moonlight when the moon is near its full phase. The Perseid shower in early August and the Geminid shower in mid-December are two examples of this.
There are quite a few smaller showers; one of these is the Orionid shower – so named because the meteors appear to originate from the prominent constellation Orion – which is due to dust from Halley’s Comet and which produces up to 20 meteors per hour when it reaches its peak around Oct. 21 each year. Unfortunately, this year the moon is full on Oct. 24, so there may not be much to see of the Orionids.
For some meteor showers, the dust grains have not yet had time to spread out all along the comet’s orbit, and instead travel in large clumps that, more often than not, travel closely with the comet (usually behind it). A classic example of this is the Leonid shower, which peaks around mid-November each year and which is associated with Comet Tempel-Tuttle, which has an orbital period of 33 years.
Normally the Leonids are a rather weak affair, producing no more than about 10 meteors per hour, however on occasion they have been much stronger than that. Tempel-Tuttle returned in 1965, and the following year an enormous meteor storm with rates that briefly reached 100,000 meteors per hour was visible from the western U.S. Tempel-Tuttle returned again in 1998, and during the late 1990s and early 2000s several strong Leonid showers took place.
Another clumpy meteor shower is the Draconid shower, so named because the meteors appear to come from the constellation Draco, which is now high in our northwestern sky during the evening hours, somewhat to the northwest of the bright star Vega. The Draconids, which peak in early October each year, are associated with a comet known as Giacobini-Zinner, which was first discovered in 1900 and which has an approximate orbital period of 61Ž2 years.
Although normally a very weak shower, the Draconids have been known to produce strong displays around the time that Giacobini-Zinner has made some of its returns.
In 1933, for example, a very strong Draconid shower with rates that briefly reached over 10,000 meters per hour was seen from Europe. Two returns later, in 1946, despite bright moonlight another very strong shower was seen from the U.S.
While there hasn’t been anything this strong since then, enhanced Draconid displays – with rates briefly as high as a few hundred meteors per hour – took place in 1985, 1998 and 2011, all of these being around the time that Giacobini-Zinner passed through the inner solar system.
Giacobini-Zinner is now once again passing through the inner solar system and was closest to the sun this past Sept. 10; indeed, this feature discussed the comet a month ago. When at its brightest Giacobini-Zinner could be detected with an ordinary pair of binoculars and is still easily detectable with small backyard telescopes as it cruises southward along the wintertime Milky Way in the constellation Monoceros, located to the east of Orion and high above our eastern horizon during the hours before dawn.
This would all suggest that we could potentially be in store for another strong Draconid shower this year. Unfortunately, the astronomers who study and model cometary dust streams have pointed out that Earth does not seem to pass close to any large clumps of comet dust this time around, and that even the one clump that could possibly produce a moderate display – briefly a rate of a few dozen meteors per hour – would take place during daylight hours here in the U.S.
Nevertheless, predicting meteor showers is not an exact science, even though we’ve learned quite a bit about this over the past two to three decades. Indeed, surprise showers still manage to occur from time to time. Thus, it wouldn’t hurt to check the Draconids this year just in case they have such a surprise in store for us.
Any Draconid shower that we might see will take place on this coming Monday evening, Oct. 8. It so happens that the moon is at its new phase that very night, so moonlight will not interfere in any way.
Will the Draconids manage to put on some kind of decent display for us, despite predictions to the contrary? There’s only one way to find out . . .
Alan Hale is a professional astronomer who resides in Cloudcroft. Hale is involved in various space-related research and educational activities throughout New Mexico and elsewhere.