The July Skies

Use binoculars to glimpse little Mercury during the last week of July. It will appear near to the east-northeast horizon just before dawn, below much brighter Jupiter.

Venus sparkles very low in the west at dusk. It is the brightest object in the sky except for the sun and the moon.

Reddish Mars glows low in the east-northeast before sunrise. On the morning of July 22, it will be very close to brighter Jupiter.

Beginning in the second week of July, look for giant Jupiter low in the east-northeast dawn sky.

Saturn appears as a steady pale yellow dot in the southwestern sky after evening twilight ends. Even the smallest telescope will allow you to see this planet’s beautiful ring system. With a larger telescope, on a night with “good seeing,” you’ll be able to view the black Cassini Division between the A and B rings.

INCOMING COMET ISON – SIZZLE OR FIZZLE?

“This comet may be one of the brightest in history.”

– Raminder Samra, MacMillan Space Centre, Vancouver, Canada

Few events are as dramatic as a bright comet appearing in our night sky over a period of several months. Well, a big comet is headed toward the inner solar system right now. And, best of all, there is a possibility that this comet may be big and bright enough to be seen even during daylight.

The first humans to see this comet were two amateur astronomers in Russia. Last September, Vitali Nevski and Artyom Novichonok were observing with a 15.7 inch reflecting telescope near the city of Kislovodsk in the North Caucasus region of Russia. When they first detected the comet it was just an obscure speck in the night sky, 100,000 times fainter than the dimmest star that can be seen without optical aid. While looking over their CCD camera images, they noticed a dim point of light in the constellation Cancer that didn’t correspond with any known astronomical object. Subsequent observations at various observatories confirmed that the object was a comet. Since the telescope they were using belongs to the International Scientific Optical Network, the comet was given the acronym ISON.

Comet ISON is called a sungrazing comet because, during its closest approach to the sun on Nov. 28, it will come within 800,000 miles of the solar surface. That’s more than 100 times nearer to the sun than Earth. The resulting tremendous tidal gravity and heat may cause the breakup of ISON. But if the comet holds together during its closest solar approach, its brightness might allow sightings during daylight for a short time. And it could continue to be a dazzling spectacle in the predawn sky throughout December.

Amateur astronomers in Chautauqua and Warren counties should be able to view ISON in small telescopes beginning in August and September. Toward the end of October, it should brighten and become visible without optical aid. Since it will appear close to the bright star Regulus and then near to Mars, these two brighter objects will help observers to locate the comet.

In November, ISON will become even brighter, and it will pass through the constellation Virgo, appearing close to the bright, blue-white star Spica and the planet Saturn. When it passes closest to the sun on Nov. 28 (Thanksgiving Day), the solar radiation could possibly transform the comet into a really brilliant object.

During December, ISON should be visible in the western sky after sunset and in the eastern sky before sunrise. It will grow dimmer as the month progresses and, hopefully, will have a long comet tail that could stretch for possibly tens of millions of miles. People should be able to see it from anywhere on Earth, although the best view will be from the Northern Hemisphere.

Readers of this Star Watch column have to understand that comets don’t always live up to the hype that precedes their appearance because they are notoriously unpredictable. When a comet is first spotted many millions of miles from Earth, there is simply no way to tell what its appearance from Earth will be months later as it rounds the sun. A lot depends on its structure and chemical composition and whether or not it breaks up into smaller pieces that possibly evaporate. Its brightness also depends on how much gas and dust is discharged from the icy rock core as it encounters heat from the sun. Large cracks can develop from the solar heat, allowing huge plumes of gas to be ejected which then form a halo surrounding the cometary nucleus. The bigger the debris halo and tail, the more reflective and, therefore, brighter the object appears. When discovered, this comet was 625 million miles away and appeared very bright relative to its distance from Earth, so, hopefully, it has the potential to be really bright when circling the sun if it doesn’t disintegrate. Possibly, it will be the brightest in human history but keep in mind that it could be a spectacular dud, difficult or even impossible to see.

The ancient civilizations, with their lack of scientific knowledge, considered comets as omens of doom. However, through science, we now understand them to be simply periodic icy visitors from the outer reaches of the solar system that circle around our sun and then return to deep space. Most of these objects come from the Oort Cloud, a cluster of billions and billions of frozen clumps of rock and ice in orbit around our sun at a distance of about one light year. These clumps are thought to be leftover debris from the formation of our solar system, and they represent the oldest solar system objects that are still in their original, pristine condition. Once in a while gravity will influence one of these clumps, and it will leave the cloud and enter into its own orbit around the sun. These cometary orbits are enormous and, in fact, many comets circle the sun only once and never return. Sungrazing comets have been known to approach speeds of 100 miles per second.

Editor’s note: This monthly guide to the stars is from the Marshall Martz Memorial Astronomical Association and The Post -Journal. For further information, contact the M.M.M.A.A. at www.martzobservatory.org.