As some of you may know, there has been another comet passing near the Earth on its periodic orbital path. It is known as a “short period” comet because it completes one orbit around the sun about every 6 years. Even so, it was not discovered until just 24 years ago. It went undetected for many years because it had not come closer to the sun than about 2 AU (astronomical units, 1 AU is an earth orbital distance). That has changed thanks to the influence of Jupiter. An article in the October 2010 issue of Sky and Telescope explained that 3 close passes to Jupiter in 1982, 1971 and 1947 have shifted Comet Hartley’s orbit closer to the sun. This time, it passed just 0.12 AU from the Earth on October 20th. It will reach perihelion (closest to the sun in its orbit) this week on the 28th.
On the night of the 13th, Mike P and I pointed the Harken telescope at Comet Hartley. We obtained a series of images which I have assemble as an animated GIF movie file shown below. These frames were taken only 40 seconds apart in time, so the whole movie shows the movement in just 12 minutes.
We thought that the comet might actually occult a star, but it was anothe near miss as the processed image shows below:
Its path through the night sky also took it right past another object that I have been watching – epsilon Aurigae. I have been keeping track of the light variations from that unusual variable star (see other blog post) and caught Comet Hartley as a smudge on the frame. I estimated it was about magnitude 6.3 in this image.
You can read more about Comet Hartley here:
There are finder charts in case you want to try with binoculars.
Oh by the way, you may be hearing more about this comet soon. NASA’s Deep Impact probe is still snapping pictures. It was re-directed to make a near pass to Comet Hartley on November 4th and take pictures from about 600 miles in distance. Pretty cool!