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Perseid Meteor Shower Arrives

The annual Perseid meteor shower is upon us as it is every August 11th-ish. While the actual peak this year is expected on the morning of Thursday, August 13th, the Perseids are known for putting on a decent show for days leading up to the peak. The coincidence of the new moon makes the 2015 shower well-positioned to be an impressive one.

Watch this space for photos!

Two Perseids go their separate ways a little after midnight on August 12th.
A single Perseid makes itself known above the CaliforniaStars Observatory (August 12th, 3:00AM).

Skies are looking good to start the hunt for Perseids.
iPhone 6 panorama at GMARS.
So what is a meteor shower? Every meteor shower is the result of Earth passing through the debris field of a comet. That means that every meteor shower is associated with a specific comet. In the case of the Perseids, the culprit is Comet Swift-Tuttle, which has a 133-year orbit and most recently went around the Sun in 1992. As a comet approaches the inner solar system it warms up and begins to expel gas, dust and small bits of debris. While the comet continues on and returns to the outer solar system it leaves behind a trail of debris. Since there is no air and wind in space (in the traditional sense) to blow away the trail of debris, it pretty much stays out there. If the orbit of the comet was such that its debris trail crosses somewhere along Earth's orbit, the two paths will intersect at some point. When that happens, it's likely that a meteor shower will be produced. As Earth travels along its orbit, it collides with the little pieces of debris (very little, most the size of a grain of sand or a very tiny pebble). The friction from colliding with Earth's atmosphere causes the tiny speck to heat up and vaporize in a matter of milliseconds or longer for larger pieces. We see it as a very quick streak of light.

Meteor showers are named for the constellation from which they seem to radiate. If you were to record the apparent path of each Perseid meteor you saw, they would all trace a path back to the constellation Perseus. Of course, the constellation from which they seem to radiate is just a coincidence and a matter of perspective. The constellation just happens to be in the background – There's no actual connection between the stars that make up the constellation Perseus and meteors from the Perseid shower.

As Earth travels along its orbit the part of the Earth's surface that faces its direction of travel changes due the fact that it is also rotating on its axis as it revolves around the Sun. Sometimes the planet will happen to travel through a comet's debris field with its sunlit side. In this case, we miss the peak of the meteor shower because it happened during the day. Even though bits of debris are hitting Earth's atmosphere and burning up, daylight is just too overwhelming for any of the meteors to be visible. But if Earth makes its way through the thickest part of the comet's debris field when its night side faces its direction of travel, and you happen to be under the night sky when that happens, you will likely experience the spectacle of a meteor shower peak! The number of meteors you can see during the peak of a meteor shower varies widely for the various annual meteor showers (the Perseids are just one shower among dozens that happen every year – such as the Geminids, Leonids, and Orionids to name a few) and from year to year for the same shower. The United States is in night time and it is facing the direction of Earth's forward motion in its orbit when the planet passes through the trail of debris left by Comet Swift-Tuttle! On top of all this, the new moon occurs just a day after the expected meteor shower peak, which means there will be no Moon light to interfere your ability to see the meteors!

There's one more variable that impacts the impressiveness of a meteor shower – being under dark skies. If you're trapped in the light pollution of an urban or suburban setting, you won't see as many meteors as if you were under dark skies, far away from cities.

So, here's what to do and what to expect...

  • Get under dark skies. You simply won't see many meteors from light-polluted cities.
  • Get a comfortable chair, dress appropriately for your weather, and lean back.
  • Perseids radiate from the constellation Perseus, which will rise in the NE. Lean back far enough so you can see a good portion of the sky, not just the NE portion. While they radiate from the NE, they can appear anywhere in the sky.
  • You'll need to stay up late. Watch the sky from midnight till about 3 or 4AM!
  • During the peak, you may see 30-60 or meteors per hour (that's 1 every other minute or more).
  • Enjoy!


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