August 2012

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 August 17th. For August, your best viewing nights will be from August 8th to the 22nd. The Star chart below is set for Florence, SC on August 15th at 10 pm.

Curiosity Arrives at Mars:
You won’t have to stay up late to see it, and you can’t use your telescope to watch it, but it will be nice to know that in the early morning hours of August 6th , NASA’s Curiosity Rover will attempt a landing on Mars. We have had some great rovers studying the surface of Mars over the years, such as Spirit, Opportunity and Sojourner, but Curiosity is much bigger. In addition to its size, about the size of a car, Curiosity will carry much more sophisticated equipment than used on any other rover. Curiosity’s special onboard laboratory will offer our best chance to discover if any form of life is presently on Mars or if any existed in Mar’s distant past.

The following image compares the size of Curiosity on the right, with two of our previous rovers.

So, we wish Curiosity well as it enters Mar’s atmosphere at 13,000 miles per hour, and lands on the surface 6 ½ minutes later.

The Perseids Meteor shower:
The Perseids meteor shower is a favorite for many observers because it occurs during the summer, so you don’t have to worry about getting up early for school the next day. The shower should peak on Saturday night August 11th and early on Sunday morning August 12th.  This year, even the adults won’t have to worry about going to work the next day.

For the new readers, it is important 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, and these orbits are usually above or below the plane of the planets in the solar system. A comet’s orbit can be as short as a few years, or as long as thousands of years. 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, however, they do not disperse into the solar system, but instead they 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 at certain times of the year, see 1 through 4 below.

When the Earth passes through one of the comet orbits, we experience a large 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.

Rules of meteor shower viewing: No binoculars, telescopes or any optical aids are needed, just use your eyes. Due to the position of the Earth and the stars during a particular entry into the comet’s orbit, the meteors appear to be coming from a particular constellation, thus the name of the meteor shower. Therefore, the Perseids meteor shower is centered in the constellation of Perseus, which rises about midnight in the northeast on August 11th.

This brings us to another aspect of watching meteor showers; time. For most meteor showers, or for meteor viewing in general, the best viewing is after midnight.  The reason is based on the positions of the Earth and you the viewer as the Earth runs into the 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; a good analogy is like running through falling raindrops. Remember, you will still see some meteors before midnight as the graze the upper atmosphere. The sketch below may help to better explain this concept.

So lie on the ground on a blanket, or use a chaise lounge chair to view the shower, using a standard chair may result in neck pain. Look in the direction of Perseus (northeast), but be aware of your peripheral vision since meteors may also appear overhead or toward the north or south. Don’t forget to bring snacks and drinks.

Naked Eye Sights:  The Perseid Meteor Shower.

Binocular Sights (7 to 10 power):  Use only to search for more Messier Objects, never for meteor showers.

Telescope Sights (60-100mm):  This month is your last chance to see Saturn in the southwest between 9 and 10 pm.

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