Moving on from the Blue Moon to the Perseids

Did you see the "Blue Moon" last Friday? Wasn't blue was it? The term "Blue Moon" is just one of those things that get attached to something. In this case two full moons in one calendar month. It is a name for something that happens rarely, like "Once in a blue moon."

On our plate now is another rare -- well, annual -- event that astronomers look forward to, the Perseid meteor shower. It is especially anticipated now because there won't be any moon to interfere like it has for the last couple of years.

The Zenith Hourly Rate (ZHR) for the Perseids is listed at about 60 per hour, or about one a minute. However, meteor showers are not known to stick to schedules. I recall one year there were Perseids visible every few seconds.

Another good thing about the Perseids, they are usually good for a show on the day before and the day after their peak period, which this year is on the evening of Wednesday, August 12, into the early morning hours of Thursday, August 13.

What causes a meteor shower? Meteors are generally small bits of debris--usually no bigger than a grain of sand--left when a comet passes around the Sun and back out into the outer reaches of the solar system.

A meteor shower occurs when Earth passes through this debris trail and the small bits enter the atmosphere and heat up due to friction giving off the tell-tale glow we see as a meteor. Sometimes these meteors are called shooting, or falling stars.

The comet that left the trail that causes the Perseid shower is called Swift-Tuttle, and has an orbital period of 133 years. The last time it was in the inner solar system was 1993 and it won't return until July of 2126. It is a comet that has been known to observers for more than 2,000 years.

The reason this particular shower is called the Perseids is because it seems to radiate from the constellation Perseus which will be rising in the east at about midnight MDT. Perseus, as you will recall, looks like a giant capital "A."

The best time for viewing the shower is between midnight and about 4 am MDT. That is when the side of Earth we are standing on is pointed toward Perseus and just like driving into a snow storm the meteor streaks seem to be coming right at you.

Now, here comes the "but." But, Perseids can appear anywhere in the sky, so as you are out observing, scan the entire sky looking for them.

Some ideas for a successful meteor hunt. 1. Dress warm, just because it is summer does not mean the early morning hours are warm. 2. Bring either a blanket or reclining lawn chair so observing the sky will be easy. 3. Bring your favorite beverage (non-alcoholic preferred) and some of your favorite munchies to help stay awake. 4. Bring some friends, it is always more fun with a group, and 5. Be patient, remember what I said about meteor showers not operating on a schedule.

SKY WATCH: Third-quarter moon, Thursday, Aug. 6. Since you are outside watching the Perseids, keep your eyes out for the surrounding constellations. The square of Andromeda us to the upper right -- an autumnal constellation; the Summer Triangle is directly overhead, and as the session wears on watch as the winter constellations of Taurus, the Bull, and Orion rise over the eastern horizon.

NEXT WEEK: The Perseids are here and more astronomical blathering.