Aug 202017

Last night I took images of a comet. My standard exposure length of 300 seconds was too long and during that period the comet moved enough to smear into a streak rendering the images useless for analysis. The video is an animation of 11 300 second exposures and shows the amount of movement over 55 minutes. In this case, North is to the top.

Currently, the comet is between Mars and Jupiter and above the plane of the ecliptic but headed south to where most of its orbit lies.

I will try a different tracking technique and exposure duration later tonight to see if I can get accurate astrometric data to report to the MPC and to get a prettier picture of the tail.

 Posted by at 13:34
Feb 112017

Comet 45P’s motion over one day brought it above my treeline about an hour earlier than Thursday night. Unfortunately, the Moon’s daily motion brought it higher in the sky and closer to the comet. These combined to lessen the amount of time I could image the comet.

Honda-Mrkos-Pajdusakova (45P) [C:3x300s]

Thursday night the mount was tracking at the sidereal rate. This is the rate the Earth rotates using the stars as the reference. This is why the stars are round after a timed exposure.

An object’s orbit in the solar system can be accurately modeled by 6 numerical values known as orbital elements. Once enough observations of a solar system object are taken, those 6 values can be derived. The Minor Planet Center (MPC) publishes the orbital elements once they are calculated. In this case we are discussing comet 45P and depending on where the comet is in its orbit, the gravitational effects of other objects (say Jupiter or the Earth) can change its orbit and, as a result, the calculated orbital elements. These values can change fairly quickly. My first pointing attempt Friday night left me with an empty image of stars. With the comet nearing the Earth, the orbital elements from Thursday night were no longer accurate and I had to download Friday’s values.

By using the orbital elements published Friday I was able to change the rate and direction the mount moved to match the orbit of the comet. But since the mount is now matching the comet’s movement and not the Earth’s rotation, the stars get streaked. This is why the comet looks natural even though the exposures were 300 seconds long. The image is a stack of three 300 second images.

 Posted by at 17:29
Feb 102017

I stayed up a little later (earlier?) than usual to see if the skies would still be dark enough to get some images of comet Honda-Mrkos-Pajdusakova (45P). Yesterday the comet rose above the eastern horizon just after 1 AM. Unfortunately, my eastern tree line has an elevation of 53° and the comet didn’t clear the trees until 5 AM, leaving just 35 minutes of dark sky. So, after taking pointing and test exposures, I was able to get twenty 60 second exposures before the PTO sky meter measured the sky starting to brighten.

Honda-Mrkos-Pajdusakova (45P) [C:20x60s] Exposures correlated to the stars.

Chart generated with Cartes du Ciel

Predictions made last December forecast the comet to be naked eye visible after perihelion on the 31st. But once it passed the Sun and started its outbound trip the comet did not meet the forecasts; not even close. The most obvious difference is the complete lack of a tail. Pre-perihelion photos show a small tight coma with a long thin tail. One current theory is the comet came close enough to the Sun to sublimate most of the surface volatile material leaving just enough to form the now large diffuse coma.

Honda-Mrkos-Pajdusakova (45P) [C:20x60s] Exposures correlated to the comet.

It is obvious from the above image how fast the comet is moving. The image shows only 60 seconds of motion yet the comet is badly streaked. The comet is currently traveling about 51,000 mph, but the apparent motion is primarily due to how close it is to the Earth, and right now the comet is quickly getting closer. The comet will pass perigee tomorrow morning (the 11th) at 2 AM (CST) at only 7.7 million miles.

The fact that the comet is so diffuse is what is preventing naked eye visibility and makes it a difficult binocular target as well. The approaching Moon is not going to make seeing the comet any easier for the next several days.

 Posted by at 15:16
Mar 032016

Comet 67P/Churyumov-Gerasimenko holds the distinction of being the first comet to be orbited by a spacecraft as well as the first to have a probe soft land on its surface. After a 10 year trip the Rosetta spacecraft entered orbit and on November 12, 2014 dropped its lander (Philae) on to the nucleus. The primary purpose of the mission was to characterize the comet and its behaviour during its perihelion passage on 13 August 2015. The comet, with its attendants, is now heading back out into deep space and will return to visit the inner solar system in 2023.


67P/Chuyumov-Gerasimenko [C:15x120s]

This image is a stack of fifteen 120 second exposures with the images registered to the comet. The image is very noisy as the Moon was very close and there was some faint wispy clouds overhead.
Chart generated with Cartes du Ciel

Chart generated with Cartes du Ciel

FYI, the comet symbol on the chart is not an indicator of the tail orientation. Also, notice the obvious difference between the comet’s predicted position in the chart versus the actual position in the image stack.
 Posted by at 18:15
Mar 172013

Comet C/2011 L4 (PANSTARRS) was discovered by University of Hawai’i astronomers using the first commissioned telescope of the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS).  The comet, discovered in June 2011, has been visible in the southern hemisphere since discovery but since perihelion on the 10th of March 2013, the comet has made it to the northern hemisphere.  Visible low on the western horizon just after sunset, the comet is slowly working its way toward the north and farther from the sun.  This also means it has been slowly dimming as the distance from the sun increases.

[F: 1x3s]

The comet was too low on the horizon to be visible from the observatory so a field trip was in order. There is a military dropzone just south of I-10 on FL Hwy-285. The field is kept very clear and the far side of the area is a tree line a half-mile away allowing for a very low horizon. I could not find the comet with eyes only but the proximity of the crescent moon allowed finding the comet with binoculars. The comet was quite bright and I am convinced younger eyes would have had no problem seeing the comet without assistance. Currently, the comet is slowly moving north and by the last week of May will be near Polaris. It will also be too dim to see naked-eye but at a predicted magnitude of 9.3 will be an easy telescopic target.

This image is a single 3 second exposure taken with a tripod mounted Nikon D50.

 Posted by at 20:27