Friday, July 24, 2009

Caroline and the Cluster

If you ask an amateur astronomer to name a famous female astronomer, the first one who leaps to mind will most likely be Caroline Herschel (1750 to 1848). Sister to the renowned astronomer and Uranus discoverer William Herschel, she was an accomplished observer in her own right.

Although born in Germany, William and Caroline emigrated to England, where William became the royal astronomer to King George.

Caroline’s discoveries included eight comets; in fact she was the first woman to discover a comet. She also discovered 14 deep-sky objects, and she catalogued many stars and nebulas. The diminutive Caroline’s primary instrument was a modest-sized reflecting telescope, around four inches in diameter.

Let’s take a look at the brightest deep-sky object she discovered: the open cluster IC 4665 in Ophiuchus the Snake Handler. It is appropriate that we search for it in July, as she discovered it on July 31, 1783.

1) About an hour after your local sunset time, face south. If you don’t know the cardinal directions at your location and you don’t have a compass, make note of where the sun sets on the horizon. That spot is approximately west. Stand with your right shoulder to the west, and you’ll be facing approximately south.


Looking south to Scorpius and Ophiuchus
Star maps created with
Your Sky


2) Locate the distinctive curve of the scorpion’s body, just above the southern horizon. Ophiuchus (oh-fee-YOO-kuss) is a large constellation that essentially rides on the back of the scorpion. So look north of the scorpion for a large asterism (star pattern) known as the Coffin, which comprises the brightest stars in Ophiuchus. It’s known as the Coffin because it resembles an old-fashioned casket with a pointed head. We’ll take a closer look at the Coffin stars in a future post.


The Coffin asterism of Ophiuchus with open cluster IC 4665


3) Point your binoculars or small-aperture telescope just above the star Cebalrai (SEH-buhl-rye) near the top of the Coffin. You don’t want to use a large-aperture (large-diameter) telescope or a lot of magnification for an object like this with a large apparent size (the amount of sky it covers from our perspective on Earth).

Can you spot the open cluster IC 4665? An open cluster is a loose collection of stars that formed around the same time in the same nebula (gas and dust cloud). You might want to think of an open cluster as a sort of family group. IC 4665 has around 30 members in its family.


Open cluster IC 4665
Image credit: Digital Sky Survey


Hats off and a tip of the teapot to Caroline Herschel, astronomer.





Astronomy Essential: Shooting stars are meteors.

The phenomenon we call a “shooting star” is actually a bit of space rock or dust called a meteoroid burning up as it enters Earth’s atmosphere. The streak of light produced as the meteoroid is incinerated is called a meteor. Most meteoroids are very small: the size of grains of sand or grains of rice. It is the high entry velocity of the particles that produces the lovely light show.

Occasionally, larger meteoroids will survive their high-speed encounter with Earth’s atmosphere and hit the ground; these rocks are known as meteorites.


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