At perihelion November 28 (Thanksgiving Day in the United States), ISON sweeps within 1.16 million miles (1.86 million km) of our star’s center, or just 730,000 miles (1.16 million km) from its surface. The comet’s temperature should soar above 4500° Fahrenheit (2500° Celsius), providing lots of heat to sublimate ices. If predictions by the Minor Planet Center of the International Astronomical Union pan out, ISON will peak between magnitude –6 and –7, brighter than Venus. Although the comet then lies within 1° of the Sun, it might show up to amateur astronomers who carefully shield the Sun with a hand or a building.
But the best views of perihelion likely will come from a trio of solar telescopes located outside Earth’s atmosphere. The Solar Terrestrial Relations Observatory (STEREO), the Solar Dynamics Observatory (SDO), and the Solar and Heliospheric Observatory (SOHO) each supply different perspectives.
The most intriguing images likely will come from SOHO. On the evening of the 26th in North America, ISON enters the field of view of SOHO’s LASCO C3, a wide-field coronagraph that blocks the Sun’s disk and allows views of the solar corona and other nearby interesting things (such as comets). ISON remains in the C3 field for nearly four days. On the morning of November 28, the comet arrives in the narrower field of the LASCO C2 coronagraph and stays there for about 10 hours. You can access these images at sohowww.nascom.nasa.gov/data/realtime-images.html. Those from the C3 coronagraph are colored blue while ones from C2 are orange.