Thursday, October 30, 2008

Haunted Sky

It is with ghoulish pleasure that I present you with 13 spine-tingling Halloween treats— of a celestial nature. There’s something here for everyone: naked-eye stargazers, telescope observers, and armchair astronomers who just want their eyeballs exquisitely tortured with devilishly detailed astronomical imagery.

Keep reading, but only if you’re brave enough to whistle in a stellar graveyard.

1) The Coffin (naked eye)
Hanging just above the western horizon after sunset— and northwest of bright Jupiter— is the summer constellation Ophiuchus (oh-fee-YOU-kuss) the Serpent Handler. A number of the brightest stars in this constellation form the asterism (recognizable star pattern) called the Coffin, which looks like an old-fashioned casket with a pointed head.

Star maps created with Your Sky

2) Little Ghost Nebula NGC6369 (armchair)
This faint planetary nebula in Ophiuchus currently trails just behind Venus. A planetary nebula is a dying star, that is, it’s the stellar material (gas and dust) being puffed off during a moderate-sized star’s death throes.

Normally, a medium- to large-aperture (diameter) telescope is required to view the Little Ghost. However, it’s currently too low in the west after dark to get a good view. Find bright Venus in the western sky at sunset, and imagine the Little Ghost floating right behind her. Then just stare zombie-like at this beguiling image taken by the Hubble Space Telescope.

Little Ghost Nebula
Source: NASA and The Hubble Heritage Team (STScI/AURA)

3) Snake Nebula B72 (armchair)
This tortuous dark nebula in Ophiuchus is just west of the Little Ghost. A dark nebula is a dense interstellar cloud that obscures light from the stars behind it. To the observer, it looks deceivingly like a void in space. In this case, the Snake is obscuring the rich star fields of the Summer Milky Way.

Although the Snake Nebula can be viewed telescopically, it’s currently too low in the west after dark to be visible. Your consolation prize is this image that practically hisses.

Snake Nebula
Source: Tom McQuillan/Adam Block/NOAO/AURA/NSF

4) Ghost of a Cheerio M57 (telescope)
This alternate name for the Ring Nebula perfectly describes the planetary nebula’s spectral, smoke ring appearance. It can be viewed satisfactorily in even a small telescope. However, you’ll need substantial aperture, a dark sky, and a good eye to spot the faint central star that’s dying and throwing off all the ghostly material.

Look for M57 in Lyra the Harp, south of the Summer Triangle star Vega.

5) Job’s Coffin (naked eye)
High overhead in the little constellation Delphinus (dell-FINE-uss) the Dolphin is the asterism known as Job’s Coffin, a quadrilateral of four stars. Look for the Dolphin sandwiched between two geometrical shapes: east of the Summer Triangle and west of the Great Square of Pegasus.

6) Cocoon Nebula IC5146 (armchair)
North of the Dolphin in the constellation Cygnus the Swan, near the bright Summer Triangle star Deneb, is the mysterious Cocoon Nebula. This large diffuse nebula is a stellar nursery, a cloud of gas and dust where new stars are forming. Because of its low surface brightness, it’s a very challenging object to observe and is perhaps best left to the seasoned observers with large-aperture telescopes. As for the rest of us, let’s ponder what else might be hatching in that cocoon while we examine this image taken at Kitt Peak Observatory.

Cocoon Nebula
Source: Julie and Jessica Garcia/Adam Block/NOAO/AURA/NSF

7) Demon Star (naked eye)
Face north. Rising in the northeast is the constellation Perseus the Hero, which contains the notorious variable star Algol, aka the Demon Star or the Ghoul Star. Algol is a double star, and its orbiting companion star eclipses it like clockwork every 2.8 days. This makes Algol’s brightness dip suddenly and dramatically. Perhaps this eerie effect is what led the ancient Greeks to consider Algol the decapitated head of Medusa, being brandished by her slayer, Perseus. Medusa was the snake-haired creature whose frightful appearance turned anyone who looked upon her to stone. Look for Perseus just northeast of the Lazy W asterism of Cassiopeia.

8) Cat’s Eye Nebula NGC6543 (telescope)
Still facing north, you’ll find the Cat’s Eye, another planetary nebula, just northeast of the Lozenge, the asterism that marks the head of the constellation Draco the Dragon. The Cat’s Eye is a telescopic heart-thumper due to its spellbinding aqua color. Once you find the “eye,” imagine the cosmic black cat it might belong to.

9) Skull Nebula NGC246 (telescope)
Just north of Diphda (DIFF-duh), the brightest star in the constellation Cetus the Whale, is the planetary nebula known as the Skull. Here’s a Halloween trick: if your scope doesn’t pull in enough of the nebulosity to give you the skull effect, focus on the triangle of three bright stars that could be two glowing eyes and a nose. With the surrounding wisps of nebulosity giving shape to a head, the object becomes the face of a wolf. Or perhaps a werewolf?

Nebula as skull

Nebula as wolf

10) Witch Head Nebula IC 2118 (armchair)
The Witch Head is technically in the constellation Eridanus the River, however, it’s easier to think of it located just to the right of Rigel, the brightest star in the constellation Orion and the one that marks the Hunter’s left foot. In fact, light from supergiant Rigel is what’s illuminating the nebula’s dust particles and making them glow. You’ll find Orion the Hunter well up over the eastern horizon before midnight.

This diffuse nebula is immense and faint. Like the Cocoon Nebula (#6), this one’s not for the faint of heart or the small of aperture. Best we keep our distance from the gnarly-faced witch and simply gaze at her profile in this image by astrophotographer John Sefick.

Witch Head Nebula

11) The Sickle (naked eye)
A couple hours after midnight, this stand-out asterism in the constellation Leo the Lion will have risen above the eastern horizon. The Sickle looks like both a backwards question mark and the farming implement traditionally brandished by the Grim Reaper.

12) Ghost of Jupiter NGC3242 (telescope)
The bottom of the Sickle points toward this planetary nebula in the constellation Hydra the Water Snake. It should be viewable in most telescopes and will appear as a dim bluish orb. It was nicknamed the Ghost of Jupiter because, in a telescope, it has about the same apparent size as the planet. Apparent size is the amount of sky an object covers from our perspective on Earth.

Ghost of Jupiter

13) Tarantula Nebula 30 Doradus (armchair)
This Southern Hemisphere object isn’t visible to us Northerners, and it’s not even in the Milky Way, but it’s simply too creepy not to include. It’s actually a gargantuan star-forming nebula in the Large Magellanic Cloud, a small satellite galaxy of the Milky Way. However, its fuzzy “spider legs” of gas and dust make it the perfect Number 13 for this list.

Have a boo-dacious Halloween.

Tarantula Nebula