Astro Bob A look at celestial happenings in the Northland and beyond Bob King View my profile Click here to view previous posts or additional resources

This comet was far-out, man

Comet McNaught finally appeared in the clear this morning about 2:45 as the clouds departed. Look at how narrow that gas tail is! Details: 200mm lens at f/2.8, 2-minute time exposure at ISO 800 on a tracking mount. Photo: Bob King

Comet McNaught is going, going, almost gone. Clouds flitted about this morning, but it was clear enough check in on this interesting binocular comet. I had to wait until 2:45 a.m., when McNaught rose high enough above the horizon haze to get a good view. That was only 20 minutes before the swelling dawn, leaving precious little time for study.

A closer view of the comet with its two tails labeled. The dust tail, though brighter, doesn't show as well as the gas tail in the photo. The green color in the comet's coma is from cyanogen gas; carbon monoxide and carbon dioxide fluorescing in sunlight define the gas tail. Photo: Bob King

The head of the comet was a small "fuzzy star" in binoculars with a northwest-pointing tail barely visible. Through the telescope the first thing I noticed was that the dust tail had grown longer and brighter. In contrast, the gas tail was a dim, ghostly shaft of light extending far and away from its source in the bright head. Maybe thick air near the horizon was partly to blame, but this tail was fainter than when I last saw it nearly a week ago.

Even though McNaught is very low in the northeastern sky, we're lucky that the bright star Capella is nearby. Spot Capella and use binoculars and telescope to (hopefully) find the comet. Time is running out! Credit: Created with Chris Mariott's SkyMap

You've only got another six or seven days to go for McNaught. While observers in the northern U.S. and southern Canada might attempt to see it near the end of evening twilight, it's still highest in the sky and best visible at early dawn. The comet is 106 million miles from Earth and receding from us but a toasty 48 million miles from the sun. Closest approach to the sun, what astronomers call perihelion, will occur on July 2 at a distance of 37 million miles. That's nearly the same as Mercury's average distance from the sun. No surprise it's bright and sports a long tail.

Here's where the planets and comet are today if you could rocket above the north pole of the Earth and look down at the solar system. The angular "zagging of the comet's orbit is a low-resolution artifact -- in reality it's a smooth curve. Credit: NASA/JPL

As the comet approaches the sun, it will continue to get lower and lower in the sky until it's lost in the twilight glow at month's end. After perihelion, McNaught is too close to the sun in the sky to see as it rapidly moves south and fades. It might become visible again at early dawn at the end of August for southern hemisphere observers, but by then it will be much diminished in brightness and character.

This is the view of the solar system from the side. Now you can see that the comet's orbit is steeply tipped, unlike the planets, which orbit in nearly the same flat plane. Credit: NASA/JPL

C/2009 R1 McNaught, it's full name, is on a hyperbolic orbit and dropped in to delight Earthbound observers from well beyond the most distant planets. Its ancestral home is a hypothesized, roughly spherical volume of space called the Oort (Ort)Cloud that lies 50-100 thousand times the Earth's distance from the sun. That's about a quarter the way to Alpha Centauri. Astronomers estimate the Cloud contains billions of comets that have been chilling there since the beginning of the solar system. They hover like moths around the streetlamp sun and don't reveal themselves to Earth-dwellers unless jostled by the gravity of the outer planets or a passing star. The little kick they receive changes their orbits slightly and they begin a long "descent" toward the sun.

This is what astronomers believe the Oort Cloud may look like. It's a reservoir for countless comets, some of which eventually enter the inner solar system. The Kuiper Belt, which lies beyond Neptune, contains many icy asteroids and comets. Credit: NASA/JPL

McNaught began its journey many thousands, perhaps millions of years ago. As it entered the inner solar system, solar heat and radiation vaporized some of its ice -- and the dust that was mixed with it -- to form a coma or head and the two tails that show clearly in photographs. Comets are debris left over from the solar system's formation. Stuff too small and widely-spaced to have gathered into a planet.

Comet McNaught may return to the Oort Cloud or it may have it orbit bent and reshaped by mighty Jupiter into an ellipse (oval) like many other comets, becoming in time a full-time resident of the inner solar system instead of returning to the land of nearly permanent refrigeration. Or the opposite could happen. Jupiter could turn bouncer of this disco ball solar system and kick McNaught right out of the bar and into interstellar space. The large outer planets had a huge role in clearing out the solar system of debris long ago and they still wield great power today.

Good luck in your comet quest!

Posted by: rking@duluthnews.com on 6/20/2010 at 10:31 AM | Comments (0) | Permalink | Edit

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