November 2009

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 November 16^th. For November, your best viewing nights will be from November 7^th through November 21^st. The Star chart below is set for Florence, SC on November 15^th at 10 pm.

The Leonids Meteor Shower

It is that time of year again, the arrival of the most well known meteor shower of the year, the Leonids. Unlike last year, the best news is that this year the Leonids will peak early morning on November 17^th, right after the New Moon. This will give optimum viewing of the meteor shower.

In previous years, I have discussed meteor showers, and viewing hints, but for readers who missed this information, it would be best if I give a review. First, what are meteor showers? Over the eons, comets dove toward the Sun, and many remained “trapped by our Sun’s gravity, forming long elliptical orbits. These comets periodically return to the Sun, over periods of only a few years, to seventy-six years (Comet Halley) to many thousands of years. The image below shows three such comet orbits.

Comets are really large “slush balls” containing ice, gases, and rocks. As the comets orbit the Sun, there is a continual loss of matter along their orbit, and this debris also circles the Sun in the same orbit. The rocky debris will become our meteor showers; see sketch below.

So each year, our Earth passes though several comet orbital paths resulting in a meteor shower. The Leonids occur when we pass through the orbit of the comet Tempel-Tuttle, which was first observed in 1699. Now the exciting part is that the debris field is not uniform. Therefore, on some years we pass though a thin field of rocks, and on other years, we may pass through a thick/dense field of rocky debris. The Leonid shower can range from about 50 to over 400 per hour. A “normal” Leonids should give a least one meteor per minute, or 60 per hour. Scientists are predicting from 100 to over 500(!) meteors per hour this year. However, don’t set your expectations too high; meteor shower prediction is not a very exacting science. No one really predicted the amazing Leonid meteor storm in 1966. Some observers at Kitt Peak observatory in Arizona estimated about 40 meteors per sec (144,000 per hour!) Note to my young readers, there may be similar Leonid meteor storm in 2032.

Viewing methods: Eyes only, no other visual aid such as binoculars. Use lawn chairs or even better, lounge chairs, and look toward the southeast. The meteors can appear anywhere from near the horizon to directly overhead. Hot chocolate and/or coffee also provide a good addition to viewing meteor showers.

The meteor showers are named for the constellation that appears to be in the center of the meteor shower, so look towards Leo the Lion. The best time to view a meteor shower is after midnight until dawn. The reason is that from early evening until midnight, we are looking away from the direction the Earth is moving in our orbit around the Sun. After midnight until dawn, when we look up at the sky, we are now looking toward the direction the Earth is moving. Remember in a meteor shower, the Earth runs into the rocky debris. So, at 3 am, looking toward the east, we’re hurtling straight into the comet’s orbit; like running fast in the rain, but instead of raindrops hitting our face, rocks are hitting our atmosphere. Remember I said that the Leonids seem to come from the constellation Leo the Lion, well Leo isn’t well above the horizon until 5 am. So, the best viewing times may be from 4 am until 6am, Tuesday morning the 17^th. Unfortunately, this is a school or workday. Rather than staying up late to hope to see a few meteors, it might be better to go to bed early, and set the alarm for 3-4 am; and remember, there are no guarantees that it will be a great shower this year, or any year, but it may be.

The Double Cluster:

There are several deep sky objects that Messier did not feel the need to report, one of which is the Double Cluster in the constellation Perseus. This cluster is one of the beautiful sights of the autumn. It is quite easy to find with a pair of binoculars because of its close proximity to the constellation Cassiopeia. Perseus may not be too obvious to new astronomers, but the “W” asterism of Cassiopeia is easily spotted. You can see its position of the clusters on the image below.

The Double Cluster is two closely packed open star clusters. They are officially named NGC 869 and NGC 884; in another column I will discus the NGC objects. On any clear night this month check out the Double Cluster. They are best observed at low power and in a dark location. If you live or travel away from the cities, they are easily visible to the naked eye. The image below is a wide field view at about 25 power.

Naked Eye Sights: The Leonids meteor shower.

Binocular Sights (7 to 10 power): The Double Cluster

Telescope Sights (60-100mm): If you get up early to see the Leonids, or if you normally rise early, Mars is getting bright, and is in front/to the right of Leo. Saturn is below and to the left of Leo, and you will note that the ring is just beginning to “open up” again. Also, Jupiter is still a great target in the early evening.

See you next month!