April Showers or the Lyrids

Whenever a comet makes its nearest approach to the sun, some pieces break off from its nucleus. The larger fragments take up orbits near the parent comet, but some fall behind, so that the comet's path is eventually filled with these tiny micrometeoroids. Periodically, the earth's orbit intersects with a cluster of such micrometeoroids, resulting in a meteor shower as the fragments burn up in our upper atmosphere.

Meteor showers associated with certain comets occur with high regularity. They are known by the constellation from which their streaks appear to radiate. The following table lists the most common and prominent showers. The shower names are genitive forms of the constellation name; for example, the Perseid shower comes from the direction of the constellation Perseus, the Lyrids from Lyra. The dates listed are those of maximum expected activity, and you can judge the intensity of the shower by the estimated hourly count. The table also lists the parent comet, when known.

Star Words

When the earth's orbit intersects the debris that litter the path of a comet, we see a meteor shower, a period when we see more meteors than average.

Star Words

When the earth's orbit intersects the debris that litter the path of a comet, we see a meteor shower, a period when we see more meteors than average.

Maximum

Estimated

Name of Shower

Activity

Hourly Count

Parent Comet

Quadrantid

January 3

50

unknown

Beta Taurid

June 30

25

Encke

Perseid

August 12

50+

1862III (Swift-Tuttle)

Draconid

October 8-9

500+

Giacobini-Zimmer

Orionid

October 20

25

Halley

Leonid

November 16-17

10*

1866I (Tuttle)

Geminid

December 11-17

50-75

3200 Phaeton

*Every 33 years, the earth's orbit intersects the densest part of the Leonid debris path, resulting in the potential for a meteor infall rate of 1,000 a minute! Such an intersection occurred in 1999, and will happen again in 2032.

*Every 33 years, the earth's orbit intersects the densest part of the Leonid debris path, resulting in the potential for a meteor infall rate of 1,000 a minute! Such an intersection occurred in 1999, and will happen again in 2032.

You'll recall from Chapter 8, "Seeing in the Dark," that you can detect meteor showers on your FM radio or even on unused VHF television frequencies. But if it's clear outside, we suggest that you take your radio outside, and as you listen for distant radio stations to pop up, look up at the skies and watch as well. It might be hard to believe that most of those streaks of light are following meteoroids no larger than a pea. But be thankful that they are!

The Least You Need to Know

V Eight of the nine planets of the solar system are divided into the rocky terrestrial planets (those nearest the sun: Mercury, Venus, Earth, and Mars) and gaseous jovian planets (those farthest from the sun: Jupiter, Saturn, Uranus, and Neptune). Pluto, usually the most distant planet from the sun, is not categorized, though it has a lot in common with the moons of the outer planets.

V While the sun and planets are certainly the major objects in the solar system, astronomers also pay close attention to the minor bodies—asteroids, comets, meteors, and planetary moons—that tell us a lot about the origin of the solar system.

V While most asteroids are restricted to highly predictable orbits, a few cross the earth's orbital path, posing a potentially catastrophic hazard.

V Both comets and meteors present ample opportunity for exciting amateur observation.

Chapter 13

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