Comet Holmes observations 2007

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Late October 2007, it was my 2nd year in college in California, and only a year passed since I owned my newest telescope at the time, which was of the type of Schmidt-Cassegrain.


College was taken most of my time, and leaves me with little to no time to practice my Astronomy passion. However, a major event in Astronomy was on the rise. It was a Comet that starts to be visible to the naked eye in the night sky.

The starry night for most of the time, is constant, to one’s life spam at least, or even to a few consecutive generations life spam. Any change on the starry map will be very noticeable to who observe it, and the event would be considered rarer if it’s not periodic.

On the nights of October 23rd/24th, astronomers and stargazers around the world start to notice a sudden burst of brightness in the sky around the Perseus constellation area of what seems to be a new star. The news was coming early from the Canary Island and Spain, and confirmed by many across the globe.

To the naked eye, indeed it seemed like a new star, but years of stored data from many observatories and many astronomers across the years showed it is an old known comet that star to outburst in visual brightness, and expanding in angular size. The normal visual magnitude of the Comet, which is also known as Comet Holmes (17P/Holmes) was varying between 19, 17, and 14.5 most of the time in normal condition. (The brightness increases as the magnitude number get smaller. Example 1 is brighter than 9). I have to give a lot of credits to those astronomers for noticing the comet at this time of the month, and this position of its orbital period. Even as bright as the comet was, it still has a small angular size, and the tail was not as much evident, and to top it, the moon was nearly full  at the night of the outburst, as it’s phase was nearly .95 with illumination of ~94.9%. The advantage of the comet position would be its long duration that night.

The geography of planet Earth played a rule and limited how much time for an individual astronomer can have to observe the comet in one night, but there was no lack of astronomers across the globe either, and reports from the USA and later from Japan to backup the magnitude information of the comet and it’s updates start to come up. The observations showed that the comet was increasing in brightness, and reached magnitude of 4 among US astronomers, and later on to be 3.5, and 3, and settled between 2.8~2.6 in Japan.

The reason for the sudden brightness that led it to be from a difficult to spot comet even for large scopes to brightness a naked eye can detect is an eruption inside its nucleus that happened most likely by buildup of gas pockets that was integrate either by its relative closeness of its position to the Sun, or by colliding to an object in its way. The later reason is unlikely but still a good suspect.

The nucleus was estimate to be 3.4 km (2.1 miles) before the outburst.   As the weeks pass by, the comet brightness was still strong, and the visual size was expanding, until the comet coma reached an angular size of nearly 30 arc minute early on November, and since the comet is further away than the Sun, that led to the conclusion that the comet coma, or its thin temporary atmosphere reached a size larger than the Sun diameter, making it the largest single object in the solar system. The Oort cloud surrounding the solar system is larger, but arguably, it’s not a single object.

A lot of articles in the astronomy media cited University Hawaii institute of astronomy report of the comet position and its size. The position can be calculated and confirm through observation even by the amateurs astronomers, as for its size, an estimate can be made through high resolution images that were accessible to observatories.

On the personal level, the topic was getting a lot of attention in the state university I was attending for my engineering degree, and Astronomy Clubs, such the one I visit in Glandule Community College, and even telescope stores around where I lived.

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Unfortunately, I didn’t have an access to a car at that time of my life, and most of my personal viewing and observations of the comet were in a heavily light polluted cities and towns.

On Monday night of the 12th of November, I got the opportunity to use my good friend Theodor backyard in Burbank city California, who used to be a former Music professor in my university. He provided the car transportation and I used this chance to use my telescope and all the heavy equipment and accessories that came with it.  The city still is very light polluted, but the back yard blocked the direct line of sight pollution that was coming from the streets, stores, and homes.

Another plus, is the chance to use my camera attached to the telescope without the worry of dealing with nearby grumpy amateur Astronomers complaining from the light coming from the camera screen. Understandable and reasonable complain for that they kept their eye vision adapted perfectly all night long.

I start the night by setting up my telescope. The task took me about an hour to complete, and I was observing the planet mars with my eyes as it was rising in the eastern horizon. Meanwhile, my friend was checking on me and the scope as he was going back and forth to prepare his back room which is separate from the house for his night of music making. He used to major in Astronomy in his 1st year of college, before he changed it into music for once and all. He was using my binoculars which I almost always keep around next to me.

I showed him where the comet was, and to his surprise, it wasn’t that difficult to spot. Meanwhile, he was telling me the story of how he changed his major. Theodor told me, in music major, he can practice his passion, unlike in his previous major.  He recalled to me the incident where once he was playing the piano at college, and someone told him, would you like to do this often, and his answer was, I could do that for the rest of my life. The last statement is incredibly accurate.

Mars was still rising, but I couldn’t use it to focus the telescope, nor the camera on it, and the star Vega was too close to the western horizon. I needed a higher target from the horizon line. The star Capella was the answer.

After I pointed the telescope, I took a series of images to calibrate the focus. It was difficult to do so since the camera I was using didn’t have live view.  I reduced the focal ratio of the telescope to get a bigger visual field of view using an additional piece of equipment called field flattener.

After calibration, I headed for the comet, and took images both with a normal field of view, and the flattener one. The later images weren’t as satisfying as the 1st set, but had no star trails on them, and that was important. I also got a reference star to know the exact location of the comet in respect with the constellation Perseus. The reference star was HIP 16394 (HD 21584) and had a small magnitude of 7.35, and for the curious, the star distance from earth was 483.91 light year.

The comet looks so beautiful with its coma. It looked like a giant jelly fish in the sky. I used my telescope many times to observe the Moon, so when I saw the angular size of the comet in the eye piece, and the images that were produced, I knew right away that the size of this comet is indeed as large as angular size of the Moon, and since the Moon and the Sun almost shares the same apparent angular size relatively to us on Earth, I concluded then the comet, the Sun, and the Moon, are roughly the same angular size.

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In this special condition, it’s true the Comet shares the same angular size as the Sun, visually to us. However, as mentioned earlier, the Comet was a little furthermore than the Sun in term of distance, which makes it then, larger than the Sun indeed in real time scale.

I had to confirm this claim for myself with measurement too, not just with my eyes, so I pointed the telescope to a known sky object to use it for comparison. I couldn’t find something more suitable at the time than the seven sisters, the Pleiades. The images I took for the Pleiades weren’t appealing artistically, but the reason was scientific, and for scaling purposes.

I took several images of the Pleiades, most of them were out of focus and showed lots of star trails due to lack of optimum tracking, but they showed the scale perfectly, and the measurements confirmed what was observed visually.

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It was nearly 10 pm that night when I start packing up the telescope to get ready to go back to my apartment in Valley Village. It was a short, but a prospered night of observation.

I then relaxed and enjoyed the comet with my eyes only. The averted vision method was extremely useful, although I knew it was possible to observe the comet with light pollution, it still didn’t seize to amaze me.  The comet reminded me actually of the Beehive Cluster, an open cluster that is located in the Cancer constellation. They both had similar quality visually, however, the Beehive cluster needed a darker sky to be observed.

Later on, I researched more about the comet and its history. The comet according to calculations was 1.61 AU from earth on Nov-12th-2007. I used the website the heaven above to confirm this. As for its history, I couldn’t find much in my college library, and a search in the World Wide Web left me with only few physical sources that were stored in the library of Cambridge in the UK, and no  access to an electronic version that I am aware of. So, I didn’t have the privilege to take a look at those books and resources.

Yet, I found From Gary W. Kronk’s Cometography great information about the history of the comet and it’s time line beginning from its discovery in November the year 1892 by the Astronomer Holmes while gazing near the Andromeda galaxy part of the sky. This explains the name of the comet. Several independent reports came from the region including Scotland at the same time within the month.

The comet appearing size was 5 arc minute at the time of its discovery, and it was in the middle of an outburst that made it shine and easier to spot.  Holmes thought it was Biela’s Comet at 1st, which at the time was the 3rd known periodic comet and was expecting to appear in the night sky.

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Comet Holmes has nearly a 6.6 year orbital period that was near Jupiter’s orbit, which affected the comet because of the great gravitational force of the giant gas planet making its period in constant change. The changes weren’t drastic, it only added or shorten the orbital period by a year give or take.

The comet then was visiting earth night sky in 1893, 1899, and 1906. The comet was in a series of outbursts throughout the years. The most notable one was in the years 1899~1900 which had an outburst that from the historic data seems like the one observed in 2007 in term of appearing size and magnitude. The data was observed by Germans astronomers, and confirmed in California.

The historic literature that we know of didn’t have any mention of the comet again until 1964. Credits of the revival of the comet go to the Astronomical journal society and the use of computer simulation that aided the search and put the comet back in to the map of the night sky. And with the help of modern telescopes, the comet was located and found to have magnitude of 19 in average, and was observed in every return ever since.

It seem the year 2007 was a great for comets in general as it started with the arrival of the unexpected great Comet McNaught with its curved tail, and  ended with Holmes, as it was naked eye object until nearly December 14th, and continued to be within the reach of small telescope and amateur astronomers until early 2008.

Comets Holmes also arrived as expected in the year 2014, but no outburst was reported and it was an observatory level comet and difficult to spot. The comet next come back will be around the 2020, and another outburst is highly welcome of course, but not guaranteed.




History resources:

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– Gary W. Kronk’s Cometography Web Site (