December 2015

Tony Martinez

                                  Tony Martinez

Each month I will describe sights of interest in the night skies of South Carolina. These sights will be broken down into three sections: what you can see with the naked eye, with binoculars, and with a small telescope. The best time to view the night sky is at and around the times when the Moon is not visible, what is known as a New Moon; which will occur this month on December 11th. For December, your best viewing nights will be from December 3rd to the 15th. The Star chart below is set for Florence, SC on December 15th at 9 pm.

wholeskychart1

Geminids Meteor Shower:
Many meteor showers occur throughout the year but are often not very impressive, averaging only 10-20 meteors per hour. The three most watched yearly showers are the Perseids in August, the Leonids in November, and the Geminids in December. Usually the Perseids are most watched because they occur during the warm summer nights of summer vacation. The Leonids are next in importance because on a few occasions they have produced over 200 meteors per hour. The Geminids seem to be the least viewed of the three. I have been watching the night sky for many years and I have noticed that over the last ten years or so, the Perseids and the Leonid averaged only 10 to 20 meteors per hour. However, during this time period, the Geminids have been averaging 60 to 100 meteors per hour. This year, the Geminids may again shine as the best meteor shower of the year.  Astronomers are predicting as high as 120 meteors per hour.  These predictions are directed at very dark sky sites. If this year’s prediction is correct, areas on the outskirts of Florence should see over 80 meteors per hour; worth staying up late. The only downside this year is that they will peak late on the night of Sunday the 13th and early in the morning of the 14th; school and work the next day. However, the good news is that it will occur during a New Moon. Shown below: Late night December 13th looking east.

Geminids

Meteor showers should only be viewed with the naked eye, no binoculars. The reason being that although the meteors appear to come from one area of the sky, in this case the constellation Gemini (see above), they may actually appear in almost any part of the sky.  They also move too fast to see with binoculars. A lounge chair will be a good viewing aid, because one down side of constantly looking up is a stiff neck. This time of year, another problem may be the cold, so bring blankets or a sleeping bag for your lounge chair. Hot chocolate is another good viewing aid for the Geminids shower.

The Anatomy of a Meteor Shower:
For the new readers, I want to review the subject of meteor showers.  Meteoroids are small pieces of rocky or metallic debris dispersed throughout the solar system. As the Earth revolves around the Sun, we run into these meteoroids, and as they enter the atmosphere, they become meteors, and the friction causes them to quickly burn up. We see them as a short streak of light, and they are usually referred to as “shooting stars.” This misnomer is a throwback to the distant past when ancient observers really had no idea what the stars were. So on any given night of the year it is likely that you will see a few meteors streak through the sky. In addition to the meteoric debris left over from the formation of the solar system, there is another more concentrated source of meteoroids; comets.

Comets are balls of ice, gases and rocks that circle the Sun in elliptical orbits. As a comet circles the Sun, gases and ice particles are released, along with the release of some of the comet’s rocks. These rocks become meteoroids, and remain in the orbit of the comet. So after several thousand years of circling the Sun, the entire orbital path of the comet is littered with meteoric debris. Since there are hundreds of known comet orbits circling the Sun, it is logical that our Earth would pass through some of these orbits each year.

periodic_shower

When the Earth passes through one of these cometary orbits, we experience a larger amount of meteors known as a meteor shower.  On a normal night, one might see one or two meteors per hour, but during a meteor shower, one might see from twenty to one hundred meteors per hour or more.

For most meteor showers, or for meteor viewing in general, the best viewing time is after midnight. The reason is based on the positions of the Earth and you the viewer as the Earth runs into meteoroids.  Before midnight, an observer would be on the side of the Earth opposite the direction of the Earth’s movement through space. From midnight onward, an observer would now be looking in the same direction that the Earth is moving through space. Therefore, we could easily see the meteoroids hit our atmosphere; like running through raindrops. Remember, you may still see some meteors before midnight as the graze the upper atmosphere.

Now that I have carefully explained the relationship of meteor showers with comets, it is noteworthy that the Geminids shower is not associated with any comet.  It is associated with the orbit of an asteroid called Phaethon. As such, it has a much wider debris field and can yield a good display over many days; have fun.

Have a wonderful Christmas and a prosperous New Year.

camels3wisemen

Naked Eye Sights: The Geminids meteor shower on the night of the 13th and morning of the 14th. If the weather is bad that night, definitely check out the night sky a day before and after the peak night. Also enjoy the return of the wonderful constellation Orion.

Binocular Sights (7 to 10 power): Orion Nebula and the Pleiades

Telescope Sights (60-100mm): Orion Nebula

See you next month!

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