Well, over the last few cloudless nights, I managed to get some more galaxy imaging done. Galaxies are definitely more challenging targets than nebula in many respects. The dimmer nebula I’m chasing these days are challenging simply for the fact that they require much more “total integration time”. That means they generally need many hours of total exposure, and appropriately matching calibration frames, in order to come out correctly. Galaxies are a different kind of challenge, in that they are relatively small compared to most nebula. Most nebula are actually larger than I can fit in my frame these days, and to capture some of them, I would need to create full blown mosaics (expose multiple images for each region of sky, and do that for multiple regions of the sky, to cover the entire nebula). Galaxies, with the exception of a few (like Andromeda, Triangulum, and the Magellanic Clouds), tend to be a tiny portion of my frame. That means they are small in my images, so lack detail. To get detail in the area that I can resolve, I have to have exceptionally good tracking. It’s the tracking part that’s been tripping me up lately.
Over the last week, I have managed to improve my tracking performance by at least a factor of two, and for the most recent galaxy images, I managed to almost triple my tracking performance. It’s a complex endeavor, involving automatic guiding as well as periodic error correction. Once I have a more firm grasp on the topic, I’ll write an article for those of you who might be aspiring astrophotographers, and are struggling with getting round stars and good detail. Suffice it to say, I was closer to 3″ (the ” symbol here means arc seconds, where as the ‘ symbol means arc minutes; 60 arc seconds per arc minute, 60 arc minutes per degree) when I first started imaging. Today, it’s down to around 1.1″, and on one occasion recently I managed to get my tracking performance down to 0.9″. Good progress, as in the long run, once I get a longer telescope, I’ll need my tracking performance to be in the 0.1″-0.2″ range. 😉
Well, anyway, technical tidbits aside, I have a good collection of galaxy images for you today. These are, by no means, the most amazing galaxy images you’ll ever see. These are wide-field images of galaxy regions and clusters within the primary constellations of the night sky right now, namely Ursa Major (also home to the asterism The Big Dipper), and Leo. The constellation Virgo is on the rise now as well, albeit later in the evening than Leo and Ursa Major, however Virgo is home to quite a number of galaxies, including Markarian’s Chain, an arcing semi-cluster of at least 13 galaxies (probably more than that, however that is as many as can identify with my current FoV). Markarian’s Chain is part of the greater Virgo Cluster, which contains nearly 2000 galaxies. I have yet to get enough frames for Markarian’s Chain, and since it comes up well past midnight, it might be another month before I have enough data to produce an image of that. There are also a number of other galaxies in the Virgo Cluster that are part of Messier’s catalog, as well as a number of other NGC cataloged galaxies, in addition to the hundreds more that are not identified in any of the major catalogs. In the mean time, here are the galaxies of early spring: M101 (Pinwheel Galaxy), M81 and M82 along with NGC3077, all of which are in Ursa Major, M51 which is right on the border of Canes Venatici but might as well be considered part of Ursa Major’s rather large collection of galaxies, and the Leo Triplet plus NGC3593, four galaxies in the constellation Leo.
I’ve found that you can often see more detail in galaxies, when image in a wider field like this, when the image is inverted and monotoned. When the background is black, a lot of the dimmer detail in the outer reaches of galaxies becomes lost in the depths of the background sky. When inverted, however, the black stars and galaxies stand out much more.
M51 is a bit of a special case here. I was able to combine exposures from my first attempt at imaging it with my latest attempt. That gave me a total of 4h 10m of exposure time, which gave me more freedom to stretch the image without too much noise. It also helped bring out some of the faint outer halo detail of the galaxies. Here it is inverted. I noted this in my prior blog about M51, but there are a number of additional galaxies visible in this image in addition to M51 itself: