If there were such thing as an Astronomical Calendar, last year would have been the “Year of the Sun” following the total solar eclipse, the annular eclipse and the Transit of Venus. And this year it would be the “Year of the Comet.”
Comet C/2011 L4 (or just Comet Pan-STARRS), was discovered by the Pan-STARRS 1 telescope in Haleakala, Hawaii, and first made an appearance in the southern hemisphere in 2012. People were treated to a spectacular show as the comet neared an estimated brightness of around +1. People in the northern hemisphere enjoyed Pan-STARRS in March 2013. Although it’s still visible, it’s not nearly as impressive as it has been.
But in 2013 we are going to get a very special treat. Coming soon to a sky near you is Comet C/2012 S1 (ISON), which most people simply call Comet ISON. Discovered in September 2012. There is some speculation that this could be the best comet in years.
Of course, we all love seeing comets, and we also know that there’s a lot more detail available to comets than what we can see with the naked eye. So what about using iTelescope to image comets? It can be done.
And if there’s anyone who knows about imaging comets, it’s iTelescope member Rolando Ligustri who lives in northeastern Italy. I asked him a few questions about his experiences and how he got into imaging comets.
When did you start becoming interested in astronomy?
When I was young, I saw men land on the moon and fell in love with space immediately. I received my first telescope in 1973. It was a small but excellent refractor: a 76/910. With it I began to observe the sky. My first target was the Pleiades, and then Saturn. When I first saw it, I was overcome with emotion: it was a three-dimensional planet!
Then I continued to observe the sky. I only stopped when I was an officer in the Italian Navy. In 1986, I bought my first real telescope for astroimaging — to photograph Halley’s Comet! In 1995, I bought my first CCD and after that another, I imaged hundreds of objects and dozens of comets.
When did you start becoming interested in comets?
My interest began with the observation and photographing of Halley’s Comet. It was too bad that the 1986 passage wasn’t very bright. Then, with the creation of the CAST Observatory (MPC235) [an observatory in Italy], I began to study them more and more. As of today I have photographed almost 150 comets, and thanks to remote telescopes like iTelescope, I have had several of my photographs appear as an Astronomy Picture of the Day (APOD).
There is no one telescope in particular that needs to be used for photographing the comets. Every set-up in the various sites around the world can go well with astrophotography — you just need to know what you want to achieve (beautiful photograph or scientific measurements) and the size of the target. In principle, the telescopes with short focal length are useful for creating beautiful images; ones with longer focal lengths can be used for searching out details inside the coma or in the first part of the tail in addition to measurements of position and light. What is important is to always pay attention to the resolution of the telescope and the movement of the comet. If you’re making measurements, 1 pixel of blur is acceptable. However, if you’re just imaging for the pure beauty, it can move 6 to 8 pixels, which you can fix in post-processing.
Can you give advice to those looking to image comets?
As I said above, you first need to decide the field of view, both in terms of the size of the comet, or for any deep sky objects nearby. A photo of a comet must always be studied, even for how to frame it. Once you decide how to frame it and know the resolution of the instrument as well as the apparent speed of the comet, you need to determine the maximum exposure.