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Everything posted by Gary

  1. 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
  2. Gary

    Nebulae in the SMC

    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.
  3. Gary

    IC 4685

    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 2016Constellation: SagittariusR.A.: 18h 09m 28sDec.: -23° 59' 04"Photo stuff: 57 subs@s 180s ea.; ISO 800; Canon 60Da on Meade RCX400 f/8 with 0.7 focal reducer
  4. Gary

    NGC 7009 - Saturn Nebula

    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 Constellation: Aquarius 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
  5. Gary

    Fornax Cluster

    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 Constellation: Fornax 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
  6. Gary

    The South Pillars

    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 Constellation: Carina 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
  7. 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 Constellation: Dorado/Mensa 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
  8. Gary

    IC 1274

    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 Constellation: Sagittarius 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