August 2010

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 10th. For August, your best viewing nights will be from August 1st through August 15th. The Star chart below is set for Florence, SC on August 15th at 10 pm.

Perseids Meteor Shower:

The Perseids meteor shower is a favorite for many observers because it occurs during the warmth of summer, and you don’t have to worry about getting up early for school the next day. Another nice aspect of the Perseids shower is even if you only see a small number of meteors, it is fun just sitting out late at night in August under the stars. The shower should peak on the night of August 12th and early on the morning of August 13th. The Perseids shower always has the potential of a good display, but the absence of the Moon this year may result in a better than normal event. Check the weather report a few days before the 12th. If clouds and/or rain are predicted for the 12th, you can check out the skies a few days before and after the 12th.

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 throw back 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.

When the Earth passes through one of these cometary 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 meteoroid’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 10 pm in the northeast on August 12th. 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 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 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.

A celestial gathering:

Take note that in the early evening of August 13th (about 9 pm) you can view three planets and a crescent Moon. Quite a nice send off as Mars, Saturn, and Venus slowly fade into the western horizon this month. The image below shows the locations of the planets and the Moon.

Naked Eye Sights: The Perseids meteor shower on the night of the 12th. The planets Venus, Mars, and Saturn “dance” with the crescent Moon early in the evening of the 13th. The return of Jupiter late in the month.

Binocular Sights (7 to 10 power): If you stay up late to see the meteor shower, check out Jupiter and its moons in the southeast.

Telescope Sights (60-100mm): This is your last chance to view Saturn or Mars, and your first chance to view Jupiter.

See you next month!

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