Saturday, June 25, 2011

Adirondack Astronomy: The Boötid Meteor Shower

At this time of year the orbital dust from the comet 7P/Pons-Winnecke, which orbits our sun once about every six years, is the cause of the Bootid meteor shower. In 1998 and 2004 this shower had outbursts that produced up to 50-100 meteors per hour at its peak, but the surrounding years produced very few meteors.

Over the years Pons-Winnecke’s orbit has been disturbed by Jupiter and has moved the comet and the meteor stream into a slightly different orbit which has resulted in the June Boötids being hardly noticeable in recent years. One advantage we’ll have this year is the moon will be a small waning crescent, which is good for spotting some of the dimmest meteors.

Meteor showers are always a great show as long as clouds and the Moon, cooperate. They also don’t require any type of optics to get the full satisfaction. It’s actually recommended that you don’t try to view them with binoculars or a telescope because of the randomness. They radiate from a certain area in the night sky, but that doesn’t mean that they will all be visible in that one specific area, so it’s best to use your naked eye and scan the entire area of the sky.

Where to Look?
The Boötid meteor shower is in the constellation Boötes (hence the name), The Herdsman, which is quite an easy constellation to find in the night sky because of the brilliant orange star Arcturus marks the base. To find Arcturus, find the Big Dipper and follow the curve of the handle to the orange star which is the forth-brightest of all nighttime stars. If you get your skymap for the June sky it should help you find your way to Boötes which passes nearly overhead in the late evenings.

When Is The Meteor Shower?
The peak for the Boötids this year is the 27th and the 28th, but observers have reported seeing members of the shower starting several days earlier, and lasting into the beginning of July.

The History
The Boötids was first noticed by astronomers soon after sunset on June 28, 1916 in England. William Frederick Denning, an experienced observer, noted that a meteor shower was in progress when he stepped outside at 10:25pm. Denning described the meteors radiating from between Boötes and Draco as “moderately slow, white with yellowish trains, and paths rather short in the majority of cases. Several of the meteors burst or acquired a great intensification of light near the termination of their flights, and gave flashes like distant lightning.”

On the night of the June 29th Denning was unable to observe due to clouds, and on the 30th when he was able to get out for only about an hour he saw only one meteor. Denning started to wonder if its sudden appearance might be attributed to a comet. After searching through lists of cometary orbits, Denning concluded that the periodic comet Pons-Winnecke was most likely the cause.

Following 1916, two notable though weaker appearances of the meteor shower occurred during the next two perihelion dates of Pons-Winnecke. In 1921 Kaname Nakamura from Kyoto, Japan, saw 153 meteors in 35 minutes. During the period between June 26 to July 11, Nakamura was able to plot 9 points of radiant which slowly made their way southeast each night.

Recent activity indicates that the showers have weakened considerably since the 1920s. In 1968 Edward F. Turco had said that observations had revealed recent rates of only 3 to 5 meteors per hour, “with meteors being on the fairly dim side.” In 1981 David Swann from Dallas Texas wrote that on six occasions during 1964 to 1971 he only observed 1 to 2 meteors per hour. Swann noted that he had “never noticed any trains, even though I have seen several bright shower members.”

The June Boötids is not the only astronomical feature William Frederick Denning is noted for, he studied meteors and novas and he won the Gold Medal of the Royal Astronomical Society in 1898. Many craters on the far side of the moon were named after Denning as was a crater on Mars.

Photo: William Denning celebrated in Punch magazine in 1892, after his discovery of a small faint comet; below, screen capture from the astronomy freeware Stellarium showing where the radiant for the June Boötids is located.

Michael Rector is an amateur astronomer with his own blog, Adirondack Astronomy.

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Although he now lives in Clinton County, amateur astronomer Michael Rector has fond memories of spending time at Great Sacandaga and West Canada Lake where the skies are dark and the Milky Way is bright.

Michael writes about astronomy on his own blog Adirondack Astronomy and is interested in getting together with other star-gazers around the region. If you are interested in getting together for an occasional star party feel free to contact him at adirondackastronomer@gmail.com.









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