Nov. 21-30, 2013: As of Nov. 21, Comet ISON will begin to enter the fields of view of NASAs space-based solar observatories. Comet ISON will be viewed first in whats called coronagraphs, images that block the brighter view of the sun itself in order to focus on the solar atmosphere, the corona. Such images from STEREO and the joint European Space Agency/NASA Solar Heliospheric Observatory, or SOHO -- will likely be quite visually compelling. NASAs Solar Dynamics Observatory, or SDO, will view the comet for a few hours around perihelion. SDOs imagery should be detailed enough to gather information about how the comet evolves through the radiation and pressure of the suns atmosphere.
All of these observatories will have different views. STEREO-A will be the only one that sees the comet transit across the face of the sun. In SDOs view, the comet will appear to travel above the sun.
The exact dates of view for these observatories is as follows:
Nov 2128: STEREO-A HI1 sees comet
Nov 26-29: STEREO-B coronagraphs sees comet
Nov 27-30: SOHO sees comet in coronagraphs
Nov 28-29: STEREO-A coronagraphs sees comet
Nov 28: SDO sees comet (for a few hours)
In addition, ground-based solar telescopes observing in optical, infrared and radio wavelengths will all be able to observe the comet during perihelion. Such observations will provide additional information about the composition of the comet and how material evaporates off it, fueling the dusty cloud that surrounds the nucleus.
One last solar effect could impact the comet at this stage in its journey. If the sun coincidentally sends out a giant cloud of solar particles, known as a coronal mass ejection, at the right time and direction to pass the comet, it could pull the comets tail right off.
December 2013 - January 2014: If Comet ISON survives its trip around the sun, theres a good chance that it will be incredibly bright and easily visible with the naked eye in the Northern Hemisphere. In early December, it will be seen in the morning, low on the horizon to the east-southeast. In late December and early January, it will be visible all night long.
A second set of Chandra observations is planned for the middle of December to early January, when ISON will be passing through a transition region in the solar wind, where the hot wind from the Sun's sun's equator is mixed with a cooler wind produced by regions near the poles of the sun.
December 26, 2013: Closest approach to Earth will be approximately 40 million miles.
