As I was making my way through my past images, I came across one from 2017 that - rather oddly - I had not yet fully processed. This is a wide field photo of the Trifid Nebula (Messier 20). It is a perennial favourite of astrophotographers, and a relatively easy target for beginners to learn data gathering and post-processing. M20 is a stellar nursery located about five degrees west from Lambda Sagittarii and two degrees northwest of Messier 8 (Lagoon Nebula). It has the unusual characteristic of having several distinct components: reflection (blue), emission (pink), and dark (the 'lanes') nebulae, along with a prominent star cluster (NGC 6514).
Date: 02 May 2017
R.A.: 18h 00m 19.1s
Dec. -22° 48' 20.5"
Tamron 500mm f/8 catadioptric lens mounted on Canon 6D
22 subs @ 120s ea.; ISO 800
I know, I know - not the prettiest name for a such an interesting galaxy, but I didn't come up with it. NGC 2442 is an example of a peculiar, barred spiral galaxy. In this case, its peculiarity is most likely due to gravitational tides when it interacted with another galaxy at some point in its history; possibly the smaller one (PGC 21456) visible to its right. Besides leaving it with an odd shape, the interaction would have started a burst of star formation evident in its arms. The Meathook, which is approximately 56 Mly away, can be found in the constellation Volans. Although not the brightest of galaxies (sorry, Meathook), it can be seen in relatively small telescopes if you are a practiced observer and under good, dark skies.
Dates: 01 March, 2019; 05 March, 2019 R.A.: 06h 37m 08.9s Dec.: -69° 34" 16.2" Photo stuff: (subs) 37 frames @ 180s + 34 frames @ 300s ea.; ISO 800; Canon 60Da on the Meade RCX400 16" f/8; Astronomics 0.7 focal reducer
This is another of those "challenging" objects I unwisely decide to tackle occasionally. This one is worth it, though, I think. Herschel's Ray, also known as the Pencil Nebula, is a beautiful swipe of blue and pink shock waves in the constellation Vela. At 3/4 of a light year in size, it is a reasonably sized object in its own right. However, it is just a tiny portion of the truly gigantic Vela Supernova. That "remnant" is what was left after a very large star cataclysmically exploded as a Type II supernova about 11,000 years ago. The force of this destruction, in turn, created a swath of delicate nebulae across at least 8 degrees (ye gods!) of the southern sky. At its distance (815 ly), this equates to an object about 100 ly across.
The hues in NGC 2736 are due to two different types of nebulae: pink indicates an emission nebula, while blue is the light scattered off a reflection nebula. When we view this object, we are actually looking at the ripples of a sheet of gas almost edge-on.
Dates: 04 February, 2019 R.A.: 09h 03m 23.9s Dec.: -45° 30' 56.9" Photo stuff: (subs) 131 frames @ 180s ea.; ISO 800; Canon 60Da on the Meade RCX400 16" f/8; Astronomics 0.7 focal reducer
Among astrophotographers, I suspect that our moon is a seen as a bit too common to spend much time on. After all, we can observe it with the naked eye - why waste precious minutes on it when we can be chasing down some truly weird objects out there in the universe? And yet, I find that I come back to it quite often, either for a photograph or, more often, just to consider it's many features through a decent telescope or set of binoculars. There is still something beguiling about getting up close and personal with all those craters.
There are quite a few interesting features visible in this image. Three of my favourite craters - yep, I'm a guy who has "favourite craters" - are right in the middle of this image of the moon. Ptolemaeus (the larger one), Alphonsus (middle), and Arzachel (top, smallest) form a slightly curved line running along the day/night terminator. You can see a clearly defined central peak in the middle of Arzachel, and another that is a bit harder to make out in the middle of Alphonsus. These peaks are reasonably common amongst lunar craters between 15 km and ~120 km in diameter. Arzachel and Alphonsus are at the top end of this range, at 96 km and 119 km diameter, respectively (Ptolemaeus is 153 km wide, so no peak). These pointy mountains are created in the initial impact, which has such force that the central rock rebounds upwards much like the water does when a pebble is dropped into it.
In the bottom left quadrant, we see some larger and smoother expanses. These are "seas" or mares, so-called because pre-telescope civilizations believed them to be large bodies of water. The larger, middle one, which has a more blue-gray appearance, is Mare Tranquillitatis (Sea of Tranquillity); the site of the first lunar landing.
This one is well-named. The Little Gem Nebula subtends a tiny visual angle; just 22 by 15 arcseconds. For those visitors unfamiliar with astronomical measurements, look at the back of your hand while it is at arm's length covering part of the sky. Point your little finger upward. It's width is about one degree. Take that width and divide it by 3600. That is one arcsecond - as I said, tiny. It's no wonder we need good telescopes and clear, still skies to view some of these objects.
The Gem Nebula is a planetary nebula (PN) that sits about 6.4 kly away in Sagittarius. Like all PNs, it is the remnant of a star that began its life weighing somewhere under 8 times our Sun's mass. In its final stages of life, such a star expands to become a red giant, then the core collapses into a white dwarf. This core bombards the gas shell with such a high level of radiation that it lights up. With very thin shells, we are better able to see the edges than the middle, which is why so many PNs appear as ring-like structures to us. The Gem is obviously an exception - quite bright across its entire width, giving it an apparent magnitude of 9.39. The mottled appearance arises from the fact that NGC 6818's gas envelope actually has two layers. The inner one is shaped a bit like a vase, while the outer one is more like a regular bubble. The overall teal-blue colour likely comes from ionised oxygen (Pottasch et al., 2005).
PNs have quite short lives by astronomical standards; usually less than 10,000 years. In an analysis of its spectra, Hyung et al. (1999) have suggested that NGC 6818 is about 9,000 years old so it is well along its lifespan. I know the feeling, Little Gem.
Date: 11 August, 2018
R.A.: 19h 44m 02s
Dec.: -14° 09' 29"
Photo stuff: 14 subs @ 180s ea.; ISO 800; Canon 60Da on RCX 16" f/8
These are a collection of gas nebulae in the Small Magellanic Cloud. Chadwick and Cooper, in their excellent book "Imaging the Southern Sky", have named the collection The Magnificent Seven (tilt your head to the right to see why). The photograph is an example of narrow-band imaging. The term narrow-band refers to the fact that the filters used during the data collection process allow light only from very specific regions of the visual spectrum in which electrons are jumping between energy levels. In this case, the image is a composite of the light from hydrogen (H-alpha @ 656.28 nm, reddish; H-beta @ 486.00 nm, blue) and oxygen (O-III @ 500.70 nm, greenish). Research astronomers will use these bands - and many others - to discover much about the nature of an object. Astrophotographers tend to use them like a palette of paint, although we often are quite interested in the same things as the pros but at an amateur level. The other benefit of narrow-band imaging for astrophotography is that it can be done in full moonlight. Because the moon does not emit light in these ranges, moonlight is, essentially, ignored by the camera sensor. The trade-off is that one needs an enormous (!) amount of exposure time to get even half-decent results.
Date: 26 July 2018
R.A.: 00h 47m 47s
Dec.: -73° 14' 04"
Photo stuff: 12 subs @ 300s ea. for each band; ISO 1600; Canon 60Da on Meade RCX400 16" f/8; 0.7 focal reducer.
This image covers a massive star formation region approximately 4 kly away, and contains several nebulae. The largest is the emission nebula IC 4685, in the central portion of this photograph. The dark, dust lane of Barnard 303 snakes across it and points to the bright, white star (V3903 Sgr; an Orion-type variable) in the middle right. The blue reflection nebula on the lower right is NGC 6559. In the lower left corner is fainter IC 1275. It is possible that the emission nebulae are part of a river of hydrogen connecting to M8, the Lagoon Nebula, which is a nearby neighbour.
Date: 11 July 2016 Constellation: Sagittarius R.A.: 18h 09m 28s Dec.: -23° 59' 04" Photo stuff: 57 subs@s 180s ea.; ISO 800; Canon 60Da on Meade RCX400 f/8 with 0.7 focal reducer
This wee object is a bit of a challenge to capture & process, but worth the effort. Planetary nebulae typically subtend a very small visual angle; this one is no exception at approximately 30 x 24 arcseconds. The Saturn Nebula sports some very clear ansae (the two bright knots in the 'rings') and a very pretty blue-green halo that suggests ionised oxygen. Aller's (1961) spectrograph seems to confirm this (Kaler, 1997). It is no great surprise, given the quality of optics at that time, that Lorde Rosse (~1848) thought that it might be a planet similar to Saturn, and thus gave it its current name. We now know that that its core is a very hot, collapsed star, surrounded by an envelope of gas that was pushed out by stellar wind after the collapse. The distance to NGC 7009 is, apparently, difficult to determine; some estimates state it being as close as 1400 ly, while others suggest it is up to 4000 ly away.
Date: 24 August 2017
R.A.: 21h 04m 12s
Dec.: -11° 22' 13"
Photo stuff: 93 subs @ 180s ea.; ISO 800; Canon 60Da on Meade RCX400 16" f/8
These four are a suite of galaxies that are part of the Fornax cluster. Clockwise from top left: NGC 1375 (34 Mly), 1380 (86 Mly), 1373 (61 Mly), & 1374 (59 Mly). There are plenty of other galaxies visible in the background. Look for the elongated smudges of light.
Date: 10 October 2016
RA: 03h 35' 57"
Dec: -35° 05′ 04.1″
Photo stuff: 32 subs@300s ea.; ISO 800; Canon 60Da on Meade RCX400 16" f/8; .70 focal reducer
The Carina Nebula, where the South Pillars region exists, has an incredible array of fascinating objects and processes. In this image, for instance, we see pillars - also known colloquially as "elephant trunks" - of dust in which stars are being born. The best example in this photo is in the lower left quadrant. Recent research (McLeod et al., 2016) has suggested that such pillars are likely to disappear once the star comes into being due to a process known as photoevaporation, in which the powerful stellar wind from the new star literally blows away its cocoon.
Date: 20 March 2018
R.A.: 10h 45m 29.1s
Dec.: -60° 03' 21.9"
Photo stuff: 20 subs@180s ea.; ISO 800; Canon 60Da on Meade RCX400 f/8; .7 focal reducer
There is rather a lot going on in this image. IC 1274 is the circular structure in the top, middle-right section of this photo. It is an HII region, sitting on the near edge of a seriously large molecular cloud known as Lynds 227. A dark nebula (Barnard 91) defines the top edge of the nebula. The bright star in the center of IC 1274 is a young, energetic B0 V star (HD 166033); current thinking is that this is the star that has blown this massive bubble (Dahm et al., 2011). The nebula, itself, contain many stars in the B0-B5 range, which suggests that this is a population of new stars. The entire image is part of a highly productive stellar nursery that contains several fascinating deep-sky objects.
Date: 12 July 2018
R.A.: 18h 09m 29.9s
Dec.: -23° 42' 36.3"
Photo stuff: 58 subs@180s ea.; ISO 800; Canon 60Da on Meade RCX400 16" f/8; 0.7 focal reducer
This one was unplanned. The sky cleared, I stepped out into the backyard, and there was Jupiter about 3 degrees from a just-past-full moon. I grabbed a few shots and created this composite. The composite was necessary to show all the objects, of course, because exposing for the moon completely dims Jupiter and loses its Galilean moons, while exposing for Jupiter makes the moon look like the lens is staring at the sun. In the end, I processed three separate frames (Moon, Jupiter, and the Galilean moons) as they appeared through the viewfinder.
Date: May 21, 2019 (about 01:00)
R.A. (approx.): 17h 22m 10s
Dec. (approx.): -21° 07' 50"
Photo stuff: Exposure times: Moon = 1/640s and Jupiter = 1/4s; ISO 400; Canon 6D; Tamron 500mm f/8 catadioptric lens
A while back, I had picked up a "new" (to me) Tamron 24 mm lens. I decided to do some wide-field, night-sky photography to try it out and, eventually, came up with this image. The Moa (in NZ) or the Emu (in Australia), seen in profile, is a series of visually connected dark regions in this portion of the Milky Way. Look for the two bright stars in the middle of the image. These mark the neck and shoulder. Just above and to the right is the head and beak, which, to astronomers, goes by the unlovely name of Caldwell 99 ("The Coal Sack Nebula"). Just above that is the Southern Cross. Moving down and to the left from the two pointer stars, we see the body of the bird; further down are its feet.
The dark areas are not empty regions. Rather, most are dust lanes and dark nebulae that block the light from the background stars. This dust is extremely fine - generally smaller than smoke particles - so it takes large amounts of it to screen out starlight. Astronomers can use specialised telescopes and sensors to peer through this dust to find what it is hiding.
The Moa is easily visible in Canterbury most of the year from a good dark site on a clear night. Note, though, being the clever bird it is, it seems to be doing a head stand around 22:00 during the mid- to late winter evenings. As of the date of this post (05/09/2018), it appears to be just completing a back flip in the southwest. Look for it to right itself in the southeast by the beginning of April, around the same time in the evening.
Date: June 19, 2017
Image centre (HD 131376):
R.A.: 14h 55m 58s
Dec: -60° 54' 21.3"
Photo stuff: Canon 6D with Tamron 24mm at f/8; 11 frames at 120s ea.
NGC 346, which resides in the Small Magellanic Cloud (SMC), is an open star cluster with surrounding nebulosity. At magnitude 10.3 and having a smallish size (~14 x 11 arcseconds), it is relatively easy to spot with a small telescope. This photograph was taken through H-alpha, H-beta, and OIII narrowband filters, which reveal the different densities of ionised hydrogen and oxygen gases in NGC 346 and the surrounding N66 gaseous region. My guess is that the apparent structural elements of the nebula in this image are likely the result of high-velocity stellar winds causing interstellar gas to pile up but I can't seem to find a good reference for this.
Although the SMC is a typical dwarf galaxy (that is to say, old and not creating many new stars), the NGC 346 & N66 region is a stellar nursery, shining with the light of many young, bright O-type stars. Nota et al. (2006) suggest that some are as young as 3 to 5 million years old (practically a baby, by stellar standards). The nebula also contains one of the brightest stars in the SMC - the very hot Wolf-Rayet star, HD 5980 - and the supernova remnant SNR0057-7226.
It is clear from this image that I'm still very much at the beginner's stage of narrowband imaging, although I'm encouraged by the fact that this time last year I had just started to consider using this sort of filtration. Actually, I'm still genuinely surprised when I can get any sort of an image with a procedure that is this complex. It is very rewarding, though, so I'll just strap on the mental crampons and continue to scale this learning curve.
Dates: 18 August, 2018; 25 August, 2018 R.A.: 00h 58m 51s Dec.: -72° 11' 09"
Photo stuff: all filters 20x180s + 6x600s ea.; ISO 800 for the 180s subs; ISO 1600 for the 600s subs; Canon 60Da on the Meade RCX400 16" f/8
Post-processing notes: Narrowband composite created with MaxIm DL6; H-alpha(656.28 nm); OIII (486.00 nm); H-beta (500.70 nm); all 100%
This is a wide field image of the Large Magellanic Cloud. NGC 2070 (The Tarantula Nebula) is clearly visible at centre right, an N11 (The Bean Nebula) is in the lower left corner. In fact, the LMC is chocka with what astronomers refer to as DSOs, or deep space objects. Almost any condensed knot of light has a designation in one or more astronomical catalogues. The central bar of the dwarf galaxy is clearly visible in this image. It is thought that some of the LMC's spiral arms were ripped off in tidal interactions with the Small Magellanic Cloud and our own, much larger, Milky Way galaxy, which just goes to show that it's a galaxy-eat-galaxy universe out there. The LMC can be seen straddling the border of the Mensa and Dorado constellations, and is approximately 163 kly away.
Date: 21 October 2016
R.A.: 05h 23m 35s
Dec.: -69° 45' 22"
Photo stuff: 50 subs@120s ea.; ISO 800; Canon 60Da with Canon 28-135mm; f/5.6