The Perseids (August's Annual Meteor Shower)

August is upon us and that means it's time once again for the Perseid meteor shower.

Animation Credit: NASA MSFC

The Perseids are without a doubt one of the most popular meteor showers of the year for stargazers, largely due to the fact that the shower occurs in August. The peak date for the Perseids is Thursday, August 12, 2010. As the new moon for August is on the 10th this year, it should prove to be a very exciting shower. This is one of the longest meteor showers of the year, beginning July 17 and lasting until August 24. Even if your weather is unfavorable for meteor viewing on the peak date, there are plenty of chances to catch these "shooting stars" before the shower ends.

The full moon this year falls on the last day of the shower, August 24. Although a full moon will diminish meteor viewing to a slight degree, the full moon of August will be the most distant moon of the year. This distance makes the August moon the smallest of the year. Very definitely a plus for night sky watchers!

The best viewing for the Perseid meteor shower is as far from city light pollution as possible. Look to the northeast after midnight in the Northern Hemisphere. The best viewing will come in the hours closest to the dawn. The Perseids are named as such because they appear to come from the constellation Perseus, which at this time of year is just a bit to the east of the constellation Cassiopeia.

The meteors seen during the Perseid shower are actually debris left by the comet Swift-Tuttle as it continues on its 130-year orbital path around the Sun. Although the meteors appear to be fairly large to the naked eye, the debris causing them is generally about the same size as a grain of sand; however, a few may be similar in size to a marble or a pea. This stream of debris is known as the Perseid cloud and the majority of the dust within this cloud is approximately one thousand years old. There is also within this cloud a fairly new filament of dust left by Swift-Tuttle in 1862. Meteors originate from this filament at a much higher rate than from the rest of the debris stream.

Activity from the Perseid meteor shower was first recorded in the Chinese annals, which state that in the year 36 AD "more than 100 meteors flew thither in the morning". This August shower is also known as the "tears of St. Lawrence", since there is an abundance of meteors at the time of the festival in Italy for St. Lawrence on August 10.

The peak of the shower on August 12 should show, under optimal conditions, somewhere around 60 meteors per hour. The first hourly count, also called the ZHR (Zenithal Hourly Rate), was provided in 1839 by E. Heis from Münster, Germany. Lambert Adolphe Jacques Quételet of Brussels, Belgium, is credited with the actual discovery of the shower. In 1835, Quételet reported the activity that appeared to be emanating outward from the constellation Perseus.

So, grab a lawn chair or a blanket, find a nice, dark location and relax and enjoy the show! Binoculars can be helpful in locating faint meteors and tails but the best viewing is done with just your eyes. These meteors move extremely fast, traveling at speeds of up to 133,200 mph (60 kps) and many could be missed while using any visual aids.

Photo Credit: Nick Ares

Author Resource: Written by Starr Hendon

Meteor Showers (A Condensed Listing)

There are dozens of meteor showers each and every year. Listed here are several of the annual showers, including viewing dates, Peak dates and the Zenithal Hourly Rate (ZHR). In a nutshell, the ZHR is the number of meteors per hour you could expect to see in optimal conditions: new moon and no clouds, away from city light pollution. These numbers are not however a guarantee. Some showers with a high ZHR can be disappointing for several years and then put on a spectacular show. Showers with a low ZHR will occasionally astound viewers with a massive display. The thing is, you just never know!

Photo Credit: Nigel Cooke

Quadrantids (QUA)
Jan. 1 - Jan. 5, Peak Jan. 3, ZHR - 120
The first meteor shower of the year, the Quadrantids is one of the best and also one of the shortest. The peak of this winter shower lasts only a few hours. Although this shower typically produces in excess of 100 meteors per hour at its peak, the cold and overcast conditions of January keep most watchers indoors. Recently NASA teams took extreme measures to get decent views of this quick shower: they took an airplane to the Arctic Circle and rose above the clouds for viewing.

Alpha Centaurids (ACE)
Jan. 28 - Feb. 21, Peak Feb. 8, ZHR - 6
Although a very weak shower in terms of meteors per hour, with its over three-week duration, chances are good that on a cold, clear night a brilliant "shooting star" will be seen.

Gamma Normids (GNO)
Feb. 22 - Mar. 22, Peak Mar. 13, ZHR - 8
This rather small shower comes from the rather small constellation Norma, located in the Southern Hemisphere. Situated between Scorpius and Centaurus, the constellation's name is Latin for normal. The Latin word refers to a right angle, quite appropriate considering the constellation resembles a carpenter's square.

Lyrids (LYR)
Apr. 16 - Apr. 25, Peak Apr. 22, ZHR - 15
The Lyrids are a fairly steady shower, averaging 10 meteors per hour. On occasion the Earth will pass through a thicker part of the dust trail of Comet Thatcher. What then follows is a meteor storm. During one such storm in 1982, viewers were treated to 90 Lyrids per hour. The best time for viewing this shower is during the darkest hours before dawn.

Eta Aquariids (ETA)
Apr. 19 - May 28, Peak May 5, ZHR - 60
The outbound particles of Halley's comet produce this rather lengthy shower, best seen in the Southern Hemisphere. This shower is noted for producing a very high percentage of meteors with visible trains, almost 50%, making the Eta Aquariids the strongest annual shower in the Southern Hemisphere. For a week around the peak date, over 30 meteors may be seen per hour.

Alpha Capricornids (CAP)
Jul. 3 - Aug. 15, Peak Jul. 30, ZHR - 4
A low rate shower best seen from the Southern Hemisphere.What makes this shower stand out is its bright, vividly colored fireballs that frequently fragment while in flight. This is an ideal shower for the patient photographer.

Perseids (PER)
Jul. 17 - Aug. 24, Peak Aug. 12, ZHR - 60
The Perseids are undoubtedly the most well-known in the Northern Hemisphere, largely due to the time of year in which this shower occurs. The ZHR has fluctuated wildly in the last twenty years, most likely due to the reappearance of Swift-Tuttle, the parent comet of the Perseids. In 1991 and 1992, the ZHR was reported to be over 400 per hour.

Orionids (ORI)
Oct. 2 - Nov. 7, Peak Oct. 21, ZHR - 20
Produced by the inbound particles from Halley's comet, this shower has remained fairly consistent in the past twenty years. The Orionids can be seen equally well from both hemispheres; however, viewers in the Southern Hemisphere generally see twice the number of meteors per hour as those in the north.

Draconids (GIA)
Oct. 6 - Oct. 10, Peak Oct. 8, ZHR - Varied
Parented by the periodic comet Giacobini-Zinner, the hourly rate is impossible to predict. In both 1933 and 1946, this shower's ZHR was in the thousands. In 1998, viewers in Japan and eastern Asia were treated to over 500 meteors per hour, as reported by the Nippon Meteor Society.

Leonids (LEO)
Nov. 14 - Nov. 21, Peak Nov. 17, ZHR - Varied
This shower is quite noted for bright, different colored meteors that leave long-lasting trains. Composed of particles from the Comet Temple-Tuttle, this shower produces brilliant displays when the comet is close to Earth, often becoming meteor storms. In one of the most magnificent storms in recorded history, over one hundred thousand meteors fell per hour east of the Rocky Mountains in North America in 1833.

Geminids (GEM)
Dec. 7 - Dec. 17, Peak Dec. 13, ZHR - 120
Relatively new in space time, the Geminids were first noted only 150 years ago. The parent object, asteroid 3200 Phaethon, was discovered in 1983 by the Infrared Astronomical Satellite. High hourly rates and yearly reliability make this a shower of choice among seasoned meteor watchers. It is thought that this shower is producing more meteors each year and is definitely one to keep an eye on.

Two artists' portrayals of the Leonid Meteor Showers in 1866 and 1833, respectively

Author Resource: Written by Starr Hendon

The Quadrantid Meteor Shower (First Shower of the Year)

The Perseid meteor shower is without a doubt the most well-known meteor shower of the year. With the Perseid shower occurring in August, many people are able to lay out under the sky at night and enjoy watching the “shooting stars” blaze a trail across the sky. August 12th, the peak night of the shower, has always been a date that is marked on my calendar.

Photo Credit: hanz_222

A much lesser known shower is the Quadrantids. Peaking this year in the early morning hours of January 3rd, this shower produces more than 100 meteors per hour. With such an awesome display and an impressive per hour count, why aren’t the Quadrantids as well-known as the Perseids?

Weather is very definitely a factor. In much of the United States, the first part of January is rainy and snowy, basically being overcast. Put cold on top of that and not many people are willing to bundle up and go stare at the sky for a couple of hours, even if they’re lucky enough to get a clear sky. Oh, how I am hoping for a clear sky!

Another factor is the shortness of the shower. Unlike the Perseids, the Quadrantid shower lasts only a few hours. Prof. A.C.B. Lovell wrote in his classic book Meteor Astronomy, “useful counts of the Quadrantid rate were made in [only] 24 Januaries out of a possible 68 between 1860 and 1927. … The maximum rate appears to have occurred in 1932 (80 per hour) although the results are influenced by unfavorable weather.”

To view the Quadrantids shower, find the Big Dipper (Ursa Major). In the early part of January the Big Dipper is positioned so that the “bowl” is up, with the “handle” pointing down. Look below the handle to see the point of origin for the shower.

The meteor shower became known as the Quadrantids because of its emanation from a now obsolete constellation called Quadrans Muralis (the Mural Quadrant) located on some 19th-century star atlases near the point of meeting between Hercules, Draco and Boötes (which to me has always looked like a kite flying, fairly easy to pick out).

If weather (or cold) is a deterrent for you, you don’t have to miss the first meteor shower of the year. Tune into SpaceWeather Radio for a live audio stream from the Air Force Space Surveillance Radar. When a Quadrantid passes over the facility, you will hear a “ping” caused by the radar’s powerful transmitter echoing from the meteor’s ion trail. During the shower’s peak, the soundtrack is guaranteed to entertain.

Look to the sky an hour or two before sunrise to watch this phenomenal sight. January 3rd will be a date I mark on my calendar in the future. Happy skygazing!

Author Resource: Written by Starr Hendon