Even though it’s a galaxy-viewing season, I wanted to shoot a nebula for a change. This is my take on the Rosette Nebula (Caldwell 49) – a giant star-forming complex in the Monoceros constellation of our home Milky Way Galaxy. It is 130 light-years in diameter and located 5,200 light-years away from us. In the centre is an open star cluster NGC 2244, the young stars of which create massive shock-heated winds that blow the ionized bubble in the centre and excite the nebula’s gas to emit the red light.
The Rosette sets early this time of the year, so I shot it over three evenings to collect enough photons. The image nearly fills the frame of my camera, so there is plenty of resolution. Zoom in – it’s mesmerizing!
For my second photoshoot after deciding to give a serious effort to come back to astrophotography I chose another famous target – The Leo Triplet. I caught it during a short break in the clouds. The members of this group of galaxies are M65 (right top in the image above), M66 (right bottom) and NGC 3628 (the Hamburger Galaxy, bottom left). They are about 35 million light years away from us.
This shoot was done on a tracking mount, but without guiding, so I used 41 sub-exposures of 25 seconds each (so-called light frames). The relatively short exposure times were needed to avoid the trailing of the stars. My polar alignment was pretty good, though, so the tracking worked well. I used a stock (unmodified) Sony a7r mark IV camera on an 81-mm (478 mm focal length) refractor telescope with the aperture of f/5.6. The ISO was set to 800, following an example I saw online. For calibration, I took 25 dark frames (same exposure length as the light frames, with the lens cap on) and 25 flat frames (2-sec exposures with the same ISO and focus as the light frames, uniformly illuminated by a tracing LED light panel through a couple of T-shirts).
The image below is a wide field, which I cropped in to get the top image.
Generally, I think not much would be possible in this area of amateur astrophotography if people would not share they experiences in online forums and in their blogs. So here is a bit of what I learned in this photoshoot: for shooting the flat calibration frames, while it is common knowledge to select the exposure in such a way that the histogram peak of the resulting images is roughly in the middle or slightly towards the left (dark) side of the light intensity range, it is also crucial to make sure that the shutter speed is long enough to average out the banding caused by the LED light source. Since the ISO is fixed (it needs to match the light frames)
I was quite pleased with this image after stacking the images in the Pixinsight software. I did make a few beginner mistakes, though. The main one is that I decided to go for a second target during the same night instead of collecting more photons of these galaxies. Since then, I have aquired some new tools and techniques, both for the image acquisition and the processing, so I am looking forward to revisiting the Leo Triplet when the skies clear up. Waiting for a cloudless, moonless night is an exercise in forced patience – a benefit of the astrophotography hobby, I suppose.
My serious interest in photography started with astrophotography almost twenty-five years ago, in a pre-digital era, with an Olympus OM-1 camera and an 8″ Schmidt-Cassegrain telescope. My wife and I, together with a bunch of friends and fellow graduate students, would bring the telescope to the top of a mountain above our campus and spend cold nights taking turns looking at faint smudges in the eyepiece. The astrophotography was exceedingly difficult, but the observational astronomy was fun in its own right, and it also lead me to terrestrial photography, first as a hobby, and later professionally.
Now I am getting back to astrophotography and discovering that it is an entirely new world, comparing to when I left it. Not that the objects in the sky changed much, but my ability to observe and photograph them has been brought to a different level by the developments in technology.
For my first comeback attempt, I selected M81, a.k.a. Bode’s Galaxy (on the left in the photo above). It’s a neat galaxy to photograph because of its brightness (apparent magnitude of 6.9) and the fact that it has a neighbouring galaxy – M82 (The Cigar Galaxy, on the right in the photo above) that fits nicely in the same field of view of a telescope (mine is an 81 mm refractor with a focal length of 478 mm, coupled with a full frame mirrorless camera). So you get to see two galaxies, one face-on and one from the edge, for the price of one.
I made the image above by stacking forty-two 25-sec exposures taken at ISO 800. The telescope was on an equatorial mount, which provided tracking. No guiding was used in this shoot (hence the relatively short exposures). I actually shot more images on the previous night, when the wether was better, but I messed up the flat calibration frames (note to self: make sure the exposure is longer than 2 sec when shooting flats using a light panel to avoid banding). The photos below are closer crops on M81 and M82.
Bode’s Galaxy is 96 light-years in diameter (about half the size of our Milky Way), and it contains more than 250 billion stars. Its light travelled for about 11.8 million years before I caught it in front of my house.
Tonight, I had a chance to photograph the full moon from my front yard. The March full moon is known as the Worm Moon, Crow Moon, Sap Moon, etc. I particularly like the poetic names given to it by the North American indigenous people: “the Eagle Moon” of the Cree or “the Windy Moon” of the Cherokee. In many cultures, it marks the day to balance one’s life and to celebrate the beginning of the new year.
Today’s Worm Moon is interesting from the astronomical perspective because at 0:14 local time (PDT) it was passing through the northern part of the Earth’s penumbral shadow, making it a penumbral lunar eclipse. The Moon darkened only slightly, even though 96% of it was in the penumbral shadow.
I took a few shots about two hours before the peak eclipse (capturing some neat clouds in a composite image at the bottom), then again about an hour before the peak (the image below) and at the peak darkening (the image above) with a Sony a1 mirrorless camera and a 70-200 mm lens at 200 mm. The settings were: ISO 100, f10, 1/250 sec.
Worm Moon approximately 1 hour before the peak of the penumbral eclipse.Composite image of the Worm Moon approximately 2 hours before the peak of the penumbral eclipse.
I took advantage of being at a very dark-sky location (Mt. Washington skiing resort on Vancouver Island) to observe the planet Mercury at it’s greatest Eastern elongation, right after the sunset. Being the closest planet to the Sun, Mercury is notoriously difficult to see. Today, it reached its widest separation of 18.7 degrees east of the Sun.
I walked outside of our chalet in the Alpine Village and could easily see the bright planet right above the tree tops, just as predicted by my astronomy app (see below). I didn’t have any camera besides my iPhone or even a tripod, but still was able to take the above hand-held photo, thanks to Apple’s magic of computational photography.
There, Mercury is the bright dot in the lower right, just above the tree line. Well above it, on a nearly-vertical line, are the two brightest stars in the constellation of Aries, the Ram – the orange giant Hamal (“the lamb” in Arabic), whose diameter is 15 times the Sun’s, and slightly dimmer Sheratan below it. The brightest dot in the upper left of the picture is Jupiter.
Through a telescope, Mercury would have exhibited a half-illuminated waning phase, but I was happy enough to see it with the naked eye, on its best-looking day of the year and under some of the best local viewing conditions.
