Published: 2013-11-25 06:22:32
Updated: 2013-11-25 06:22:32
Posted November 25, 2013
By Tony Rice
If you’ve not yet seen Comet ISON, you may be running out of time.
Imagery from the Hubble Space Telescope less show ISON’s core to be less than two miles across. Its nearly 5 million-mile-long tail is made up of water – ice leaving the comet’s surface. Bad Astronomy author Phil Platt and the Comet ISON Observing Campaign estimated that enough water to fill an Olympic-size swimming pool is leaving the comet about every three minutes. The comet reaches a critical point in its life later this week.
ISON will reach perihelion, the closest point in its swing through the solar system, on Thanksgiving Day. Before then ISON will be visible before sunrise. After it will be most visible after sunset, if the comet survives that long.
Comets are made of rock and dust and ice and it's the ice that holds them together. Temperatures in a comet’s core can rise beyond 5000 degrees Farenheit, hot enough to melt iron much less ice, during that solar encounter. Large chunks of ice can break away in a process called “calving.” The sun’s energy may disintegrate or even evaporate its icy visitor. There is no way to predict what will happen though the appearance of a second tail has led to concerns about possible fissures within the core.
Monday looks be our last opportunity in central North Carolina to see ISON before perihelion. Clear skies are expected while overcast skies will likely spoil the view on Tuesday and Wednesday. Bundle up because temperatures will be in the teens before sunrise.
ISON will rise shortly after 6 a.m. and reach 10 degrees above the horizon (the width of your fist held at arm’s length) by sunrise at 7 a.m. Look to the southeast low on the horizon for a fuzzy green dot. Look for ISON’s dimmer tail pointing away from the sun and toward the quarter moon.
A triangle of stars above just above ISON will serve as a guidepost as well. Actually only the dimmer star on the right is actually a star – Zubenelgenubi, the brightest star in the constellation Libra. The brightest of the small triangle is Mercury (top) with slightly dimmer Saturn on the left.
If a pair of planets and a comet aren’t enough to get you out of bed a bit early, the International Space Station will make an appearance in the northwest at 6:44 a.m. rising about 1/3 up the sky setting six minutes later in the east right into the rising sun. What a way to begin the week.
If you miss ISON Monday morning, hope for the best for survival on Thursday. The comet will be visible after sunset through December and into January. Christmas night looks promising with visibility comfortably above the northwest horizon and another bright ISS pass beneath the comet.