C/2012 S1 ISON, which may become one of the brightest comets in recent years, remains hidden in the glare of day but will soon be under the constant scrutiny of a thousand eyes. During the remainder of July and early August it crosses the “frost line”. Here, at a distance of 230 to 280 million miles from the sun, the comet’s abundant water ice begins to vaporize bringing with it a steady increase in the comet’s brightness. ISON followers will recall that before the comet was lost in the solar glare in May it “stalled out”, stuck at the same faint rut for months.
Late next month it will finally crawl back into a dark sky. First visual sightings of the comet in larger amateur telescopes should happen shortly before the start of dawn when ISON will appear as a faint bit of 13th magnitude fuzz in the constellation Cancer. Northern hemisphere observers are favored at this time. Australians will have to wait until mid-September or later for it to finally show in a dark sky.
As ISON gradually brightens, professional astronomers and NASA in particular are planning an all-out campaign. Here’s a sampling of the artillery that will be brought to bear:
NASA’s Balloon Rapid Response for ISON (BRRISON) mission will launch sometime in September. A huge helium balloon will loft a 31-inch (0.8-m) telescope 23 miles (37 km) high into the stratosphere to study the comet in visible and infrared light. The atmosphere blocks infrared light, so getting above most of it is crucial to studying the comet’s carbon dioxide to water ratio which will shed light on the comet’s origins.
BRRISON observe many other targets during its flight including Comet Encke, the moons of Jupiter, the water-rich asteroids 24 Themis and 130 Elektra, the multiple star systems Castor and Mizar and, if the flight occurs in late September, Earth’s moon.
* October 1
NASA points the Mars Curiosity and Opportunity Rovers’ cameras on ISON when it makes its closest approach – about 40 million miles – to the Red Planet. Mars Odyssey and the Mars Reconnaisance Orbiter will also take photos from orbit.
* Oct. 10 – Nov. 28
The comet first enters the field of view of one of the two sun-watching STEREO spacecraft (Solar Terrestrial RElations Observatory) on October 10 and remains in view through November 28 when it makes its closest approach to the sun. Click HERE for a complete guide to STEREO’s planned observations.
Also during this time, the orbiting Chandra X-Ray telescope and Hubble space telescope will keep their eyes glued to ISON. Even NASA’s JUNO mission to Jupiter will be involved.
* Mid-late November
NASA launches a FORTIS (Far-ultraviolet Off Rowland-Circle
for Imaging and Spectroscopy) sounding rocket to measure ultraviolet light emitted by ISON as sunlight boils away its ice and dust. The data will help nail down the comet’s composition.
* November 19
Mercury flyby when ISON will be photographed by NASA’s orbiting MESSENGER spacecraft.
* November 27-30
Comet ISON enters the field of view of the SOHO (Solar and Heliospheric Observatory) sun-blocking coronagraph on Nov. 27 and exits on the 30th. Provided this icy wanderer survives the heat, we should be able to watch it swell to brilliance. There’s a small possibility NASA’s Solar Dynamics Observatory will be able to photograph the comet in far ultraviolet light when it’s closest to the sun.
* Late November
NASA’s Lunar Reconnaissance Orbiter observes the comet from lunar orbit.
* November 28
On Thanksgiving Day in the U.S. Comet ISON will zip closest to the sun, missing its blazing surface by just 680,000 miles (1.1 million km).
* December 2013
A great show is hoped for as the comet swings around the sun and appears at both dusk and dawn (depending on location) with an ever-lengthening tail. On the 27th, ISON makes its closest approach to Earth at 40 million miles.
And don’t forget – professional and amateur astronomers will use ground-based telescopes to beam in on the comet throughout its apparition hoping to learn more about what makes a comet tick.