Meteor Showers

Meteor Showers

If you look up into a dark sky on any clear night you are bound to see a streak of light shoot across the sky. With all the space junk humankind has sent into Earth orbit, that streak could be the disintegration of a man-made object re-entering our atmosphere. However, in most cases the incoming object has a more natural origin.

These sky streaks, which most folks call shooting stars, are leftover material from the creation of our solar system. It not only includes the remnants of comets and their dusty tails, but also includes small asteroid fragments. The Earth encounters this dust and debris as it revolves around the sun. In fact, each day millions of tons of material fall onto the earth’s surface.

While some of the meteors are just random particles that intercept the Earth’s orbit, meteor showers are the debris left behind by comets. As a comet approaches the Sun it “heats” up, and the ice sublimates (transitions directly from a solid to a gas, bypassing the intermediate liquid phase). This process creates a huge cloud of dust and gas, called the coma, which surrounds the comet.

In addition, the solar wind begins to impact the comet’s surface. It’s like sandblasting. Material is blown off the comet forming a tail. As the comet continues its journey around the Sun, particles in the tail are deposited along the comet’s orbit. These particles comprise the meteor stream. Most are no larger than a grain of sand, while some may be the size of a fingernail, and a few might be the size of your closed fist.

As the Earth orbits the Sun it encounters some of these dusty comet tail remnants. The meteoroids slam into the Earth’s atmosphere and become luminous as meteors when friction heats them up. They can streak across the sky in a flash, or persist for several seconds before disintegrating. They peak, or reach maximum, at the same time each year, though the number of meteors seen during a particular shower may vary from year to year. This variation depends on whether the earth encounters the dense part of the stream (high rates) or the outer fringes (low rates).

Therefore, average peak hourly rates are always given. An observer can watch the number of meteors rise to peak and decline thereafter. The duration of the rise, peak, and decline all depends upon the particular shower’s characteristics. During some years new research can suggest enhanced activity. That forecast comes from careful study of the meteor stream and its past performance.

An attentive observer will notice that meteors appear to radiate from a fixed point in the sky. Though not all the meteors begin exactly at this reference point, called the radiant, all associated shower members can be traced back to the radiant point. This effect is one of perspective, much like railroad tracks that appear to converge at an observer’s horizon. The meteors actually travel along parallel paths through space. The constellation in which the radiant point resides also lends its name to the meteor shower. For instance, the April Lyrids radiate from Lyra, and the Geminids radiate from Gemini.

However, you also do not want to stare directly at the radiant. Seldom does a meteor begin right at that point. An observer needs to scan as much of the sky as possible, constantly shifting one’s gaze high and low, right and left.

If many meteors appear to be coming from another area of sky, then shift your gaze and concentrate on that region. Still, it doesn’t hurt (much) to constantly scan as much sky as possible without straining your neck!

If a meteor shower peaks around the time the radiant point is close to your horizon, you may experience some meteors known as Earthgrazers. These meteors skim across the top layer of our atmosphere at a very shallow angle, thereby producing very long trails and trains of dust from the horizon to a point overhead. We use to call these meteors “skippers.” They hit the atmosphere, but like a rock skipping across the water, they often bounce back out into space for a second. Gravity wins out and pulls the meteor back into the atmosphere once again. Depending upon a variety of circumstances, multiple skips can be seen.

The speed of the particles entering our atmosphere depends upon how the Earth intercepts the meteor stream. When the Earth intercepts a meteor swarm head on, the velocity of the meteor entry is the velocity of the meteor plus the orbital velocity of the Earth totaled together. If we catch up to a meteor swarm, the final entry velocity is the difference between the meteor’s velocity and the Earth’s. Speeds in between are the result of the various possible directions of the meteor swarm orbit relative to the orbital direction of the Earth.

A meteor’s velocity does have an effect on the meteors themselves. A slow, solid, nickel-iron meteor has a greater chance of surviving the atmospheric plunge, while a fast, more loosely held together stony meteor wouldn’t have a prayer. Only dust-size particles of the latter will normally survive, unless the object was very large originally. Those larger members of the shower can fragment into smaller particles, each producing its own streak of light and luminous train of dust.

Meteors can even explode in a bright terminal burst. If an explosion is heard, pieces of the meteor can fall to the ground as meteorites. These very bright meteors are called fireballs or bolides. Any observation of a fireball accompanied by an explosion should be reported to Skyscrapers, Inc. as soon as possible. Many of our members will be observing the major meteor showers at various locations throughout Rhode Island and nearby Massachusetts (weather permitting of course). If enough data is collected as soon as possible concerning an exploding meteor, it may result in locating meteorites on the ground.

Also, you might even observe a “stationary” meteor. What, you may ask? Think about it. If the meteor looks like a point source of light as it enters the atmosphere that must mean it is heading directly towards you! So duck!

Don’t worry about being struck. Just remember, three quarters of the Earth is covered with water, so a higher probability exists for the meteors to land in that medium. But put your mind at ease. While reports of people being hit by a meteorite are difficult to verify, in recent history perhaps two to three have been confirmed struck. The odds are astronomical. On the other hand, damage to personal property has resulted from meteorite impact. In fact, two houses were struck 11 years apart (1971 & 1982) in Wethersfield, Connecticut.

Though we have highlighted twelve meteors showers (both major and minor) on this website, there are dozens upon dozens of other showers. Our list is for the casual stargazer who wants to maximize their chances to see more than a handful of shooting stars without spending a lot of time.

Keep in mind that a bright Moon can dramatically reduce the number of meteors one can observe. If it is present during your observations, try to hide it from view using some trees or a building if at all possible. At least keep its light from directly entering your eye. And don’t forget that light pollution will also severely limit how many meteors one might see. Some showers produce brighter meteors than others. Many variables are involved.

Furthermore, observe with a friend so you won’t fall asleep during the possible inactive gaps. And, do try to observe comfortably in a reclining lawn chair. If it is cold, bundle up in a sleeping bag. If it is warm and muggy, and you find yourself on the mosquitoes’ banquet menu, use plenty of insect repellant. With Triple E and West Nile Virus more prevalent in certain regions of the United States these days, I would recommend extreme caution observing from those locations.

And one final note: don’t get too comfy out there. Many moons ago, during a Geminid meteor shower watch from Seagrave Observatory, it was clear when we started observing, but sometime during the night we all fell asleep. When we awoke we realized some clouds had paid us a visit, since we were all covered with a dusting of snow. Moral of that story is...stay awake while meteor observing during the winter, otherwise they may have to pick you up with ice tongs and thaw you out in the morning!!

Enjoy the beauty of the heavens.

Moon phases for 2014

Quadrantids

January 2-4

3.1

Typically, 40 or so bright, blue and fast (25.5 miles per second) meteors will radiate from the constellation Bootes, some blazing more than halfway across the sky. A small percentage of them leave persistent dust trains. This shower usually has a very sharp peak, usually lasting only about an hour.

Lyrids

April 21-23

22.4

The swift and bright Lyrid meteors disintegrate after hitting our atmosphere at a moderate speed of 29.8 miles per second. They often produce luminous trains of dust that can be observed for several seconds. They radiate from a point near Vega in Lyra. 

Eta Aquarids

May 4-6

5.9

These swift and yellow meteors blaze through the sky at 41 miles per second. About forty percent often leave long persistent dust trains behind them as they disintegrate. The normal peak rate is about 10-15 meteors per hour. Better seen in the Southern Hemisphere where it is the best meteor shower of the year. Unfortunately this shower is an old and declining one. The radiant point in the Water Urn asterism (looks like a Y-shaped group of stars) in Aquarius, does not rise very high for us New England at this time of year.

June Lyrids

June 15-16

17.4

The June Lyrids is a very low-rate shower during which you could see up to 10 meteors per hour during its peak. Practically extinct at this time. Appear to radiate from the sky not far from Vega in Lyra.

Delta Aquarids

July 27-29

1.3

At peak time about 20 bright, yellow meteors can be observed per hour. Because these meteors nearly broadside the Earth, their speed is a moderate 25.5 miles per second.

Capricornids

July 29-30

3.3

The Capricornids are characterized by their often yellow coloration and their frequent brightness. They are also slow interplanetary interlopers, hitting our atmosphere at around 15 miles per second. Though you can expect only 15 meteors per hour at best under dark sky conditions, the Capricornids are noted for producing brilliant fireballs.

Perseids

August 11-14

16.3

This shower produces about 60 meteors per hour, but rates have climbed as high as 120. Its performance is fairly consistent from year to year. Usually green, red or orange, these shooting stars appear to radiate from the constellation Perseus. They hit our upper atmosphere at about 134,222 miles per hour. 

See more info on the 2013 Perseid Meteor Shower, which peaks on the morning of August 12, 2032.

Draconids

October 8-9

15.2

Expect a peak rate of 10 yellow meteors per hour under clear, moonless conditions. These are fairly slow meteors, coming in at 12.5 miles per second. They radiate from the head of the constellation Draco. This shower was once known as the Giacobinids.

Orionids

October 20-22

27.2

This shower produces a peak rate of 20 yellow and green meteors per hour, which are fast moving at 41.6 miles per second and are known to produce fireballs. They radiate from a point in the sky not far from Orion’s red giant star Betelgeuse.

Taurids

November 5-12

19.8

This shower is actually two streams, the North Taurids and the South Taurids. It produces about 5-10 bright yellow meteors per hour. They enter our atmosphere at 17 miles per hour and often fragment into multiple meteors. Taurid meteors radiate form the sky not far from the Pleiades star cluster in Taurus.

Leonids

November 16-18

24.8

The Leonids are best known for their 33-year peaks, during which 100s of meteors per hour can be observed. The last of these peaks occurred in 2001. Normal peak rates are 15-20 fast meteors (44 miles per second) . Mostly blue or green in color., with many leaving persistent dust trains behind them upon disintegrating. 

Geminids

December 12-14

21.2

The most reliable meteor shower of the year, the Geminids are characterized by their multi-colored display--65% being white, 26% yellow, and the remaining 9% blue, red and green. They come in at a moderate speed of 21.75 miles per second, therefore they are bright and often produce fireballs. They radiate point is near Gemini’s bright twins, Castor and Pollux.