Spaced Out Challenge: Five Planets & The Final Countdown

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Welcome again to the Spaced-Out Challenge. Whether you have a question about a scope, a new astronomical discovery you want to expand on, or just want to kick back and enjoy the cosmos above, come one come all on our weekly journey through space and time.

This week, we hold our collective breath as Comet ISON nears its destiny Thanksgiving Day, when it will pass just a million miles above the scorching solar surface. As it has moved out of our sight, a delightful arrangement of the brightest planets greets amateur and expert alike. Read on and I'll show you!

Five Planets in One Night
A rare treat for amateurs is observing Mercury, Venus, Mars, Jupiter AND Saturn in the same night. If you have bought a telescope or binoculars through Ace's Amazon site but haven't tried it out yet, here is a perfect opportunity to dive in. Besides the moon, planets are the most frequently observed object by amateurs, and for good reason: whereas many deep sky objects seem foggy, faint, and monochromatic, Jupiter's cloud belts, Mars, and Saturn's rings pop in vivid color in even the smallest of instruments. Unlike deep sky targets, planetary viewing isn't affected by a bright moon or light pollution, so observing these wanders requires little more than a clear sky.

Here's where to look this week.

Early evening, any night, Venus is high in the Western sky. Through a telescope it appears as a bright crescent. Try various color filters to cut down on the glare. Larger instruments may reveal a cloud feature or two:

After 7pm, Jupiter rises in the constellation Gemini, outshining any star in the sky. It will stick around until dawn, passing high overhead into the west around 6am. Its four moons make a fine grouping in binoculars, and its cloud belts and red spot are visible in small telescopes:

Set your alarms for 530am and trek outside for a triple planet treat. Mars is high overhead in Leo, while Saturn and Mercury make a lovely morning pairing right above the horizon. From here on out, Saturn will rise higher and earlier every evening, as Mercury dips back into the sunlight. Saturn's rings are an indescribably beautiful sight in any telescope:

Latest on ISON

Comet ISON has remained intact and is registering about magnitude 3.5, bright enough for naked eye observation if it wasn't being overwhelmed by the rising sun. Now, we watch our satellite observatories and wait. NASA's Tony Phillips summarizes the three potential fates awaiting this promising visitor:

#1 Spontaneous Disintegration before Thanksgiving
The first scenario, which could happen at any time, is that ISON spontaneously disintegrates. A small fraction (less than 1%) of comets have disintegrated for no apparent reason. Recent examples include Comet LINEAR (C/1999 S4) in 2000 and Comet Elenin (C/2010 X1) in 2011. ISON is now reaching the region of space, within ~0.8 AU of the Sun where comets like these have disintegrated.

Comet ISON is being observed by a tremendous variety of telescopes on Earth and beyond. If ISON does disintegrate, it would be the best-observed case of cometary disruption in history and would likely contribute vast new information about how comets die.

#2 Death by Sunburn around Thanksgiving Day

Assuming ISON survives the next few weeks intact, it faces an even more daunting challenge: making it around the Sun. At closest approach to the sun, the comet's equilibrium temperature will approach 5000 degrees Fahrenheit, hot enough to cause much of the dust and rock on ISON's surface to vaporize.

While it may seem incredible that anything can survive this inferno, the rate at which ISON will likely lose mass is relatively small compared to the actual size of the comet's nucleus. ISON needs to be 200 m wide to survive; current estimates are in the range 500 m to 2 km. It helps that the comet is moving very fast so it will not remain long at such extreme temperatures.
Unfortunately for ISON, it faces a double whammy from its proximity to the Sun: even if it survives the rapid vaporization of its exterior, it gets so close to the sun that the suns gravity might actually pull it apart.

Destroyed comets can still be spectacular, though. Sungrazing Comet Lovejoy, for instance, passed within 100,000 miles of the sun's surface in December 2011. It disintegrated, forming a long tail of dust that wowed observers on Earth.

#3 Survival
The final case is the most straightforward: ISON survives its brush with the sun and emerges with enough nuclear material to continue as an active comet. If ISON survives intact, it would likely lose enough dust near the Sun to produce a nice tail. In a realistic best-case scenario, the tail would stretch for tens of degrees and light up the early morning sky like Comet McNaught (C/2006 P1) did in 2007.

The best of all possible worlds would be if ISON broke up just a bit, say, into a few large pieces. This would throw out enough extra material to make the comet really bright from the ground, while giving astronomers pieces of a comet to study for months to come.

"I'm clearly rooting for #3," says Knight.

As new images of ISON are becoming harder to come by (it is drowning in morning twilight now), here's a surprising shot from yesterday morning, and a few documentaries.

And while we're watching docs, coblogger rdbrewer pointed me to this NOVA one that aired last week, suggesting the possible economic boom SMOD could provide instead of wiping out all of humanity:

Until then, clear skies and keep looking up!

Next Week: The Winter Hexagon and the Treasures Within

posted by CAC at 06:01 PM

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