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A Unique View of Comet ISON
This view was recorded by the Heliospheric Imager-1 ("HI-1") instrument on NASA's STEREO-B satellite on October 28, 2013. STEREO is now the 8th spacecraft to have observed comet ISON!Just a quick post to share this image and outline the two main reasons why I think this image is pretty cool:
1. It was recorded by the HI-1 instrument on NASA's STEREO-B satellite which, on October 24th 2013 became the 8th spacecraft to have observed comet ISON! (You'll recall that earlier this month, its twin, STEREO-A, became the 7th.)
2. This is a field of view that we will never have from Earth, as the STEREO-B spacecraft sits in a completely different part of the solar system to Earth, on the opposite side of the Sun.
Just to elaborate on that second point a tad, both of the STEREO spacecraft were placed into the same orbit as Earth when they launched almost exactly seven years ago. However, one spacecraft was set to travel faster than Earth ("STEREO-A", or "Ahead"), and the other set to travel slower ("STEREO-B", or "Behind"). After seven years in orbit, this now places them on the far side of the Sun from Earth, and thus gives them a different view of the solar system than we get here on Earth. Right now, as seen from the STEREO-B spacecraft, and as you can see in this image I posted, comet ISON appears extremely close to the planet Jupiter and the open star cluster M35. (Of course, in reality this is a line-of-sight effect. Comet ISON is physically nowhere near Jupiter.)
And while I'm writing, I want to make note of a couple more pieces of information. First, I saw a couple of reports online this morning that European observers have spotted ISON with their binoculars! This is very exciting news, and means that ISON is still a healthy comet that is brightening up just the way we thought and hoped it would. Admittedly these observations were made from sites with very dark skies, but it still tells us that ISON's brightness is definitely trending in the direction we want it to.
The second point of interest is that at 20:58UT today (October 31, 2013), comet ISON will pass inside the orbit of Earth! Now this doesn't mean it is near to Earth, or going to hit Earth (it's not, and won't!), but what it does mean is that its distance from the Sun is less than Earth's (average) distance from the Sun - a unit we call an astronomical unit, or AU. So as I type this ~1830UT, comet ISON is 1.00248AU from the Sun. By the end of the day, that value will be less than 1.0AU. And in exactly four weeks from today, that number will drop to just 0.012AU as it blazes its way through the Sun's outer atmosphere and hopefully emerges as one of the more spectacular comets in many years!
Keep up-to-date on the latest ISON and sungrazing comet news via my @SungrazerComets Twitter feed. All opinions stated on there, and in my blog posts, are my own.