View from Mars Hill: Just in time for Halloween, a witch head in the sky
VIEW FROM MARS HILL

View from Mars Hill: Just in time for Halloween, a witch head in the sky

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Witch Head Nebula

The Witch Nead Nebula

Pareidolia.

It’s a phenomenon most of us experience at some point but is fortunately not as nefarious as its name sounds. It is the human tendency to recognize familiar patterns or meanings where they don’t actually exist. It’s why some people see Mickey Mouse in the clouds or President Lincoln on a piece of toast.

In astronomy, it triggered a certain Flagstaff astronomer to perceive waterways on Mars, or the rest of us to see a man on the moon, the constellations, and a variety of familiar outlines in the nebulae and star clusters spread across the universe. Iconic celebrations like Halloween lend themselves to their share of examples, including ghost heads, black cats, and pumpkins.

One of the more captivating of these is the Witch Head Nebula, an eerie cloud of cosmic dust that strongly resembles a witch in profile.

The Witch Head is not visible to the unaided eye, and in fact wouldn’t be visible even through a telescope if not for reflected starlight, similar to how the moon is visible from Earth because of reflected sunlight. Astronomers classify the Witch Head as a reflection nebula — a cloud of interstellar dust that reflects light from one or more nearby stars. In this case, the starlight comes from Rigel, the brightest star in the constellation Orion and the seventh brightest in the entire night sky (in the accompanying image, Rigel is to the right, out of the field of view).

The distance from Earth to both Rigel and the Witch Head is about 900 light years. The distance separating the latter two is about the same as that between the Sun and Pluto. Despite this remoteness, Rigel is still able to illuminate the clouds of the Witch Head because of its extreme brightness, which is about 120,000 times that of the Sun.

Color images of the Witch Head show it to be blue. This is partly because Rigel is blue and also because the nebula’s dust grains reflect blue light better than other colors, such as red. This is the same reason why Earth’s sky appears blue.

The Witch Head is near the border of the constellations Orion and Eridanus. Many astronomers think it is likely the remnant of a supernova, which is gas left over from the explosion of a massive star in its final stages of life. Evidence also suggests that it may contain a stellar nursery, where young stars are forming.

German astronomer Max Wolf first noted the presence of the Witch Head, writing in 1909 that he detected traces of it in 1891. He wrote, “The nebula is composed of several streams of nebulosity, and has the appearance of foggy clouds driven by a fresh breeze.” By 1909, the object remained enigmatic to the astronomy community, and Wolf acknowledged that he didn’t know if other astronomers had seen it or not.

Edwin Hubble, of expanding universe fame, first identified Rigel as the illuminating star. Not until 1927 did the nebula pick up the nickname “Witch Head Nebula,” when American astronomer Frank Ross suggested it.

Today, the Witch Head would probably be unknown outside of astronomy circles if not for modern photography techniques that allow for spectacular imaging.

Kevin Schindler is the Lowell Observatory historian.

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