Comet Brightness Difficult to Predict
Let's be clear about the hazards of celebrating a comet's anticipated brightness--it is fraught with uncertainty. Yet let's also embrace that unknown element of Comet ISON after its close approach to sun, known as perihelion, on Thanksgiving Day 2013.
Since the early 1950's, comets have been dubbed "dirty snowballs" based on the model proposed by Fred Whipple. Basically it suggests the comet is a big chunk of very cold ice insulated by an outer layer of buying viagra over the internet dirt. As the comet nears the 100 mg viagra inner solar system and ordering levitra without a prescription heats up, the ice sublimates and vents out fissures in the ensconsing dark shell. Sunlight bounces off the ejected material, which we see as the coma and tail. The visual quality of the comet is a reflection, literally, of the veracity of the outgassing.
In recent years, after spacecraft have actually flown by comets, scientists have modified the notion, referring to comets as "icy dirtballs." They're much darker than previously expected, and images show a significant outer crust of rock.
So how come astronomers find comet brightness such a difficult thing to predict? If they go out on a limb and declare a certain outcome, they surely risk being duped by the comet's actual performance. Several factors influence comet behavior.
Imagine a fresh comet coming out of the depths of the Oort Cloud for the viagra 30 mg first time. A newcomer might have a parabolic orbit around the sun--it comes in and goes back out. That first-time comet may be carrying some volatile compounds that are easily agitated by even a modest warming. The comet could be beyond, say, Jupiter's distance when the dark crust absorbs enough sunlight that suddenly the volatiles "boil off", if I may use that term loosely. In a premature poof, the volatiles are expelled and the comet appears bright.
Heck, if it's bright by Jupiter, the reasoning goes, it outta be stunning once it gets near the sun. Not necessarily so. An early poof may be just that. The rookie comet may brighten momentarily, then settle down to a more modest showing.
On the other hand, a comet whose inaugural orbit has been perturbed (e.g., by Jupiter's influential gravity) may be captured in an elliptical orbit around the sun. Again and again the veteran comet encounters the mrcatto.com sun's heat, and with each passing it loses more ice, causing it's overall composition to becoming increasingly rocky. Who knows, eventually it may become an ice-free lump orbiting ceaslessly in the dark.
A big part of the brightness guessing game is the unpredictability of buy cialis tadalafil the outgassing. Perhaps a comet needs to reach a thermal threshold at which a major fissure opens up, exposing fresh ice to viagra prices us the sun. A simulated rift is conveyed in the dry ice comet, pictured at left, where the white ice facilitates a vast gushing of fresh material that spews out into space. The solar wind then blows it outward in an invigorated tail. No one can declare with certainty when the breaking points of the respective comet crusts are. It's like knowing with certainty when an earthquake will occur--science is www.accessibleadventuresvt.org not there yet.
We hope the comet follows a brightening trend and cialis fast delivery the output factory doesn't shut down prematurely.
Joe Rao describes the challenges of predicting comet brightness at http://www.space.com/20347-comet-brightness-predictions-difficult.html, where he notes:
For an interesting analogy, baseball scouts like to catalogue the talents of players by looking at five general areas of performance in which one may define potential talent. Great ballplayers can hit for average, hit with power, field, run and throw.
Similarly, astronomers who catalogue potential great comets look at four general areas of performance: comets that closely approach the online ordering levitra sun, closely approach the Earth, have a favorable projection angle for viewing the tail and high intrinsic brightness.
From these criteria, Comet ISON certainly appears to be generic discount levitra a “can’t miss” prospect, though it is a new comet, which makes it more of a wild card.
So we wait and see. In the interim, let's not be afraid to celebrate Comet ISON's sungrazing, even if its eventual brightness is not well-predicted. If your expectations cause you to wait for a brightness level with surety, you may never live to experience a Comet Festival. Embrace the uncertainty now.