NGC6781

NGC 6781 is one of the better planetary nebulae in Aquila. It was discovered by William Herschel on July 30, 1788. It is in the original H400 program. My log entry on May 21, 1985 with my 10" f/5 on a good night at up to 180x reads; "Large planetary nebula whose disk is somewhat brighter toward the north end. Dimmest toward the south end with an even dimmer center. No central star seen." CCD images don't match the eye because the eye is very sensitive to the cyan of OIII and the blue of hydrogen Beta but insensitive to deep reds from H alpha and NII lines common in planetary nebulae. So my visual impression likely is referring only to the OIII and maybe H beta lines, not the red rim.

Trying to find the distance to this nebula is a problem. Most places I've checked say it is about 2 minutes of arc across, 2,800 light years away and 2 light-years across. The problem is the math doesn't work. If you say it is 2 minutes of arc across and 2800 light years away then it is only 1.6 light years across. If it is 2 light years across and 2 minutes across it is about 3600 light years away. The three figures can't all be right. So your guess is as good as mine on its size and distance. I do agree it is about 2 minutes of arc across, I get 115" by my measurement, about 1.9 minutes.

The blue star in the center is the white dwarf that remains after it's red giant stage. The star has shrunk to about the size of the earth from a size large enough to hold millions of earths. It has no energy source other than a little bit from gravitational collapse as it cools. Still, it is so small it will live for billions of years. In fact, it's quite likely that every white dwarf ever formed is still in existence today. But that's not true of the nebula. Most only last 10,000 or so years. A blink of an eye in the life of the white dwarf. This is because it is expanding rapidly. In a few thousand years it will be so large and the gasses so thin and distant from the illuminating white dwarf it will just fade out of visibility. All planetary nebula seen in the universe are very young compared to the age of even the most short-lived stars.

This is another of my early 2007 images. My skills at processing and researching were nil back then. This will have to do for now.

14" LX200R @ f/10, L=4x10' RGB=2x10', STL-11000XM, Paramount ME

Related Designations for NGC6781

NGC6786

NGC 6786 and UGC 11415 are a pair of interacting galaxies in eastern Draco just west of Tau Draconis which gave me fits and casts the nasty glare into the eastern side of my image. The pair is listed as VV414. They are about 340 million light-years distant by redshift and 350 million light-years away according to the HST website. This may be a rounding difference. The southern galaxy, NGC 6786. It is classified as an SB? Sy1 galaxy by NED and SBbc by the NGC project and SBbc? by Seligman. No one gave it a "pec" label. It was discovered by Lewis Swift on October 3, 1886. I measure its size as a bit over 100,000 light-years. That is helped by the drawing out of the arms due to interaction with UGC 11415. The CPCG says of it: "Distorted blue spiral, one pronounced and one washed-out arm." The UGC adds "Thin bright arm in direction of UGC 11415.

UGC 11415 is listed at NED as S? Sy2. Including the long arm to the north, it too is about 100,000 light-years in diameter. It is listed in the CPCG as a "Blue distorted spiral." While the UGC adds the adjective diffuse to that description. A blue field star makes seeing its core area details rather difficult at my resolution.

This pair has been imaged by the HST. Their take on them can be seen at: http://hubblesite.org/image/2289/news_release/2008-16 which shows a "little" more detail than I was able to capture.

Being far north and in the summer skies, these two were the only galaxies in NED with redshift values in the field. In fact, the rather large low surface brightness possible spiral south of the pair and third largest galaxy, in angular size, in the image isn't listed at NED at all except as an ultraviolet source (not a galaxy) as recorded by the GALEX satellite. It is LEDA 214717 according to SIMBAD and according to The Sky's database is listed at magnitude 18.4. I found nothing else on it. So no annotated image was prepared.

14" LX200R @ f/10, L=4x10' RGB=2x10', STL-11000XM, Paramount ME

Related Designations for NGC6786

NGC6789

NGC 6789 is a very small irregular galaxy in eastern Draco about 11 to 12 million light-years distant. This was determined by the Tip of the Red Giant Branch method using HST data. Redshift is useless at this close distance and in fact, the galaxy is slightly blue shifted rather than redshifted.

Its core region is full of bright blue star clouds while the entire galaxy is blue. NED classifies it as Im but the one main paper http://arxiv.org/pdf/astro-ph/0102452v1.pdf I found on it argues it is a Blue Compact Dwarf. It just doesn't seem as dense as the other BCD galaxies I've imaged but maybe that isn't a requirement. Assuming the distance is 12 million light-years I get a size of about 4,800 light-years. That certainly is a dwarf!

The HST has taken some images of it but none have been using filters that could be used to create an image anywhere close to the real color. One quickly processed image from Wiki is at https://upload.wikimedia.org/wikipedia/commons/5/54/NGC_6789_hst_09162_R814B606.png but it doesn't say what filter was used for it. Since near IR I band is useful for TRGB distance measurements this may be the frequency used. That would explain the lack of resolution of the blue star clouds I picked up as this would be picking up much cooler stars best. The paper cited above says some 15,000 or so stars were resolved by the HST image

The galaxy was discovered by Lewis Swift on August 30, 1883. This part of the sky is poorly studied for galaxies. NGC 6789 is the only one in the field with any distance data. Therefore I didn't prepare an annotated image.

14" LX200R @ f/10, L=4x10' RGB=2x10', STL-11000XM, Paramount ME

Related Designations for NGC6789

NGC6791

NGC 6791/Berkeley 46 is an often overlooked star cluster in Lyra. Everyone goes there for M57 the ring nebula and sometimes for its globular M56 but few ever stop by to see this cluster. Too bad as it is quite interesting and a big problem for astronomers. It is a rather large but distant cluster at 13,300 light years give or take a few hundred.

Normally star clusters are thought to form from a cold molecular cloud. As the first stars form the really big ones shine in ultraviolet light and this lights up the Hydrogen by causing it to glow its characteristic pink color but they also start to disrupt star formation by heating the dust and gas to where it is too hot to condense to form stars then blowing it away before more can form. This tends to limit the size of most clusters to a few hundred stars. But this cluster contains several thousand stars. It could be that it just didn't form the massive stars needed to disrupt star formation and thus more stars formed. We see several other large clusters. This one though is very old. Most clusters are torn apart by the tidal forces of our galaxy and only last a few hundred million years if that. Our sun is thought to have formed in such a cluster that has since so broken up we are hard pressed to find any other cluster members due to the passage of some 4.5 billion years.

This cluster though has a star population that is about 8 billion years old and shows no sign of being torn apart. But this isn't a mystery. Its location and mass are such that the tidal forces haven't been able to overcome the gravitational force of the thousands of stars to tear it apart. Several other such clusters are known such as M67 in a previous update.

What is really odd though is that instead of all the stars being about the same age it also contains a smaller population of 6 billion year old stars and another of 4 billion years. Adding to the confusion the 6 billion year old stars are all white dwarfs, that is, dead stars that are just cooling embers today. This means this population was made up of stars all of which were more massive than our sun. Rather than a mix of masses that you'd expect. I know of no other cluster that can claim this and how it came to be is a big mystery.

But this isn't the only mystery. For that, we must go back to the original stars in our universe. After the big bang, the universe consisted mostly of hydrogen and helium. Other elements, mostly lithium existed in such small amounts as to be totally insignificant. As the first stars aged they, like today's stars, first turned hydrogen into helium for energy then helium into carbon. Really massive stars then turned the carbon into heavier elements all the way up to iron. When these massive stars died in supernova explosions they spread these elements through the universe where they were picked up by newly forming stars. So this next generation of stars had more of these heavier elements than did the first. Astronomers call these heavier elements "metals" even though many (like carbon and oxygen) certainly aren't what a chemist would call a metal. Each succeeding generation had more of these metals than the previous. So by the metal content of a star, you should be able to get a rough idea of when it formed. Since some areas of our galaxy had more metals than others this is only a rough guide and there are far better ways to determine the age of a star. Still, the two should have some agreement.

NGC 6791 is a huge exception to this. Its 8 billion year old stars contain far more of these metals than our much younger sun. No one can explain this as yet. So how this cluster got so "dirty" is a huge puzzle. Stars forming three different times and having far too many metals makes this a highly studied cluster but so far the answers have been slow in coming. Maybe one of the students seeing this update will be the one to find the answer to this or at least determine if there's a connection between the triple population problem and the metal surplus problem.

This cluster was discovered by August Winnecke in December 1853.

For more on this and Hubble's view of the very core of the cluster (it can't see the whole thing with its narrow vision) see:
http://hubblesite.org/news_release/news/2008-25

14" LX200R @ /10, L=5x10' RGB=1x10'x3, STL-11000XM, Paramount ME

Related Designations for NGC6791

NGC6792

NGC 6792 is a very large, possibly "red and dead" spiral in northeastern Lyra. It is a bit over 200,000 light-years distant by redshift and while Tully-Fisher estimates put it slightly further the agreement is quite good. I measure its size at about 150,000 light-years. NED and the NGC project classifies it as SBb while Seligman says SBb?. I'm not sure why the question mark. It has a very odd rotation curve that is centered on a point well south of the core. I didn't find any ideas why this was the case. The faint spiral arms are rather distorted, possibly due to this odd rotation curve. Could this be why it appears to be a "red and dead" galaxy? Is this appearance only due to it being heavily reddened by our galaxy's dust? I doubt it, it has places on its outskirts appear slightly blue.

It was discovered by J(acob) Gerhard Lohse in 1886. While he is credited with 17 NGC objects, only 3 were galaxies. 11 were single or multiple stars and three can't be found. An 18th object turned out identical to NGC 4319 discovered by William Herschel 89 years earlier. His is not a stellar record, or is it too stellar? While there is are craters on both the Moon and Mars called Lohse they are named for Oswald Lohse who studied surface features of some planets though, of course, didn't know of Mars' craters. While both were German astronomers I don't think they were related.

Being in the Zone of Avoidance no other galaxy in the field had any redshift data. Also, there were no asteroids in the image so I it didn't warrant an annotated image.

14" LX 200R @ f/10, L=4x10' RGB=2x10', STL-11000XM, Paramount ME

Related Designations for NGC6792

NGC6793

NGC 6793 is an open cluster in western Vulpecula about 3,600 light-years distant according to WEBDA. It is rather young at 440 million years of age. Still, I'd expect one or two red giants but I don't see any candidates. While the background is quite red and thus apparently well behind the cluster WEBDA lists the cluster's reddening at only 0.17 magnitude which is pretty insignificant. It is listed as Trumpler class IV2p which means it is pretty much lost against the background, has stars of moderately differing brightness levels and is poor in star count. At least in a color image, its blue stars really stand out from the background of fainter red stars so I have a bit of trouble with its status as IV. But visually that may be the case. This cluster was discovered by William Herschel on July 18, 1789 and is in the second Herschel 400 observing program. My visual noted from that were in a spiral notebook that never did get transcribed to a computer database. In the move from Nebraska to Minnesota, that notebook has vanished. Even after 11 years, we have boxes here that have never been opened that are buried in the depths of a storage area behind the stairs. I know I have a visual note on it from the late 80's but it's lost for now and likely forever.

I take these clusters on nights of very poor transparency as they are about all that cuts through the gunk. I tried for it on 4 different nights. One night had 2 very obscured but sharp luminance images but clouds took out everything else. I tried about 20 other luminance and color frames but conditions kept nailing me. I found one quite usable red frame, a green frame that had horrid gradients from apparently someone on the lake with a spotlight trained on the observatory. They see its apparently roofless near three-story height and put their spotlight on it to see what the heck that odd thing is. My only even possible blue frame was under very good transparency (in relation to the others) but very bad seeing. I was going to throw the mess out and put it back on the to-do list but decided to try processing it. Somehow it all worked far better than the data would have led me to expect. The vast dense Milky Way background was lost to the several magnitudes loss to clouds in the Luminance frames. The RGB were too different in quality to stack as a pseudo lum or even make into a color image. But when used to color the very limited luminance data it somehow worked. No two frames were taken at the same temperature but for the two luminance at -25C. The green was at -15C, the blue at -20C and the red at -35C. Amazing what software can compensate for.

14" LX200R @ f/10, L=2x10' RGB=1x10', STL-11000XM, Paramount ME

Related Designations for NGC6793

NGC6800

NGC 6800 is a Templer class III2p open cluster in Vulpecula. I'm assuming it is the bright blue stars that overlay a field of fainter, much redder, stars. Which of the fainter stars are members is much more difficult to determine. WEBDA gives a distance of 1000 parsecs (3260 light-years) and an age of 390 million years. Thus, some of the bright orange stars may be red giants in the cluster. It was discovered by William Herschel on September 10, 1784. It is in the second Herschel 400 observing program. That is the main reason I had it on the to-do list.

This one is posted at 1.5" per pixel as my standard 1" per pixel image scale adds nothing to this image but increased bandwidth.

14" LX200R @ f/10, L=4x10' RGB=2x10', STL-11000XM, Paramount ME

Related Designations for NGC6800

NGC6801

NGC 6801 is a rather odd spiral in northeastern Cygnus. NED classifies it as SAcd, The NGC Project says Sc while Seligman says Sc?. Note how two arms curve out of the core to the south then turn and go straight to the edge of the galaxy. The northern one seems to suddenly turn north and sort of follow the edge of the galaxy but again in a straight line. I think this more an illusion due to a small field star in our galaxy and a star knot in the arm defining a line that isn't there. But the part coming out to the edge certainly is straight. Arp had a classification for spirals with a heavy arm. Often this was straight as in the most famous example, M101. In fact, the one in M101 does go out straight then bend at about a 75 degree angle and continue on straight until it again bends at about 60 degrees and continues on straight yet again. These two arms aren't heavy but they sure are straight.

NED's redshift puts it some 190 million light-years distant. But its 9 Tully-Fisher measurements range from 143 million to 192 million with an average of 166 million and a median of 152 million. So roll a 10 sided die and see what comes up. Using the redshift value it is about 80,000 light-years in diameter. A reasonable value for a spiral galaxy for whatever that is worth. The closest measurement makes it 60,000 light-years across, also reasonable. Being in the Zone of Avoidance it isn't well studied so I don't expect this issue to be resolved anytime soon.

The galaxy was discovered on August 5, 1886 by Lewis Swift. I've not tried to view it visually. Steve Gottlieb's description at the NGC Project calls it "faint" in his 17.5" scope so it would be difficult at magnitude 13.9 in my 10" scope used for my visual work.

Though the galaxy had a supernova (well it was still preliminary when I took the image) which I've marked in the annotated image. It is thought to be a type II SN so not all that useful for determining distance. That may explain its somewhat red color. I'd expect it to be blue but some Type II explosions result in some H alpha which might be causing the reddening. Or it's just due to looking through the dust of our galaxy as this region is very dusty. But on May 21, 2011 a type Ia, SN 2011df, blew in it. Yet I didn't find it had been used to calculate a distance to this galaxy. It has long since faded away. It was located just under the "19" in the label for the new supernova. Thus well outside the visible disk of the galaxy indicating it is much larger than I'm measuring it.

I didn't know of the supernova when I took it. Only a few weeks later when I was reviewing the frames to make sure I didn't need to retake any (weather has been so bad I've needed a lot of retakes during this period) I saw a star that didn't belong. A check of David Bishop's supernova pages showed me it was discovered a month before I took my image. I see it is now officially SN 2015af.

14" LX200R @ f/10, L=4x10' RGB=2x10', STL-11000XM, Paramount ME

Related Designations for NGC6801

NGC6802

NGC 6802 is a type III1m open cluster in Vulpecula. It was discovered by William Herschel on September 22, 1783. It's not in either H400 program. WEBDA puts the age of the cluster at about 3/4 of a billion years. Rather old for an open cluster as tidal forces usually rip them apart faster than this. Could its elongated shape be due to tidal forces? I doubt it but found nothing on this either way. Its distance is about 3,700 light-years according to WEBDA and it is reddened by nearly a magnitude. Still, it has blue stars. Its main claim to fame is that it is on the end of the "Coathanger" an asterism that looks just like its name. It is located in southwestern Vulpecula.

This is another of my very early images when I did no research and my imaging and processing skills were nearly non-exist.

14" LX200R @ f/10, L=6x5' RGB=3x5'x3, STL-11000XM, Paramount ME

Related Designations for NGC6802

NGC6804

NGC 6804 is a planetary nebula in Aquila, one of many in the constellation. It was discovered by William Herschel on August 25, 1791. It is in the second H400 program. My notes from that were lost in the move to Minnesota. I've not looked at it visually since.

Distance estimates to planetary nebula tend to be guesses more than measurements. NOAO puts it at 4,200 light-years. The eastern side seems flattened. Some papers say this is due to its interaction with the interstellar medium.

This is another early image from 2007 when I did no research so the above is all I found easily. I will try and update this as time permits.

14" LX200R @ f/10, L=4x10' RGB=2x10'x3, STL-11000XM, Paramount ME

Related Designations for NGC6804