Category Archives: astronomy

archaeoastronomy, star death, supernova

A Star Set in Stone

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The supernova depiction at Chaco Canyon Copyright 2002, Mark and Carolyn Collins Petersen
The supernova depiction at Chaco Canyon © 2002, Mark and Carolyn Collins Petersen

A year ago we vacationed in Chaco Canyon in New Mexico for a couple of days. One of our goals was to hike out to the site of a pictograph drawn on a rock overhang that is said to depict the appearance of a supernova that occurred in 1054 A.D. The artist was part of the Anasazi group of people who populated this canyon during that time, and much archaeoastronomical debate centers on just what it meant for the artist to paint the scene.

It must have been an eerie sight when the explosion flared into view over the eastern horizon early on July 4, 1054 A.D. Perhaps it had some ritual meaning to the Anasazi. Or maybe it was just their way of recording a strange thing in the sky. We’ll never know, but that doesn’t stop learned astronomers and ethnographic types from tussling over what the rock record means. One thing’s for sure, the presence of a bright “guest” star must have been a surprise to ancient stargazers who knew the skies quite well. Certainly the Chinese and Japanese thought it so remarkable that they recorded it in their writings, and there’s even evidence that people living on Guam noticed this outburst and drew pictures of it on cave walls. But, apparently, few in Europe saw fit to record this apparition, although it would have been quite bright in their skies.

A Crab Nebula finder chart
A Crab Nebula finder chart (right-click to download a fullsize version)

Can we see the supernova today? Well, yes, sort of. It has faded quite a bit from the glory days of 1054 A.D. when it rivaled the full moon for brightness. To see it with any detail you need a medium-to-large backyard-type telescope and maybe even a filter or two. It’s definitely not a binocular object but if you want to just see where the Crab lies, look toward the horns of Taurus the Bull after they rise up out of the horizon clutter on these November nights. The southern horn of the Bull extends out to a star called Zeta Tauri. The Crab lies just above that star.

VLT view of the Crab Nebula
VLT view of the Crab Nebula

Of course, observatory scopes are really good at digging into the heart of the Crab and showing us the spectacular details of this explosion. Here are two of my favorites: the first is from the European Southern Observatory and the second is a combined Hubble Space Telescope and Chandra X-Ray Observatory image:

HST and Chandra view the heart of the Crab Nebula
HST and Chandra view the heart of the Crab Nebula

I often wonder what the ancient Chinese, Japanese, and Anasazi peoples would think if they only knew just what it was they were recording on their parchments and sandstone? For them, this sight was a mysterious one — another symbol of something in the sky that they didn’t understand. But they surely appreciated the beauty of the apparition — just as today we look at it and try to comprehend the stellar forces at play in the death of a supermassive star.

astronomy, astronomy news, star death, starbirth

Whoa, Horsie!

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Humans have the most amazing propensity to use animal “avatars” to illustrate things. A couple of entries back I wrote about cats in the sky. There are also sea creatures and even birds and bees up there! But the animalization of space isn’t limited to constellations. This deep-sky object is called the Horsehead Nebula — for the obvious reason. It’s actually a cloud of gas and dust that happens to lie in front of a bright, glowing cloud of gas and dust. The superposition of one over the other gives us the lovely vision of a horse’s head.

The Horsehead Nebula, courtesy European Southern Observatory
The Crab Nebula, courtesy of European Southern Observator

This high-resolution image from the European Southern Observatory takes what looks like a serene scene and shows us how very chaotic the situation is at this nebula. You can see wisps and filaments in the gases, and clouds of diffuse dust. If you look at the top of the figure you see a bright rim separating the dust from the gas cloud (also known as an H II region). Astronomers call this region an “ionization front” where the photons from the HII region are moving into the cloud. Their energy is emitted as heat, which is destroying the dust and the molecules and lighting up the gas.

Actually, the Horsehead is a short-lived object. The continual erosion of the gas and dust by the emissions from nearby stars will eventually destroy the clouds in a few thousand years. So, enjoy this deep-sky animal while we have it!

The Crab Nebula, courtesy of European Southern Observatory
The Crab Nebula, courtesy of European Southern Observatory

Also lurking within the confines of the constellation Taurus, the Bull, is the Crab Nebula, so named because through smaller telescopes it appears as a crab-like ghostly apparition. In reality, this thing is an expanding cloud of gas and dust marking the spot of a cataclysmic explosion called a supernova. It first shone in our skies in the year 1054 A.D. and was observed by the Chinese, Japanese, and very likely the Anasazi tribes of the American Southwest.

The Crab contains a neutron star near its center that spins 30 times per second around its axis, the remains of the original star. It flashes light pulses 30 times a second (making it a pulsar). In this picture, green light is predominantly produced by hydrogen emission from material ejected by the star that exploded. The blue light is emitted by very high-energy electrons that spiral through a huge magnetic field twisted around the pulsar.

Of course we don’t see any of this through our backyard-type telescopes — for most of us this just looks like a dim little glow in the sky, hidden more than 6,000 light-years away and unlikely to do us any harm.