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NGC 6380 (14,543 of 18,816)

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Tonantzintla 1

NGC 6380, C 1731-390, Cl VDBH 233, Cl Pismis 25, ESO 333-14, GCl 68, Tonantzintla 1, Cl Ton 1, Tirion's Joke for Summer, h 3688, GC 4305

RA: 17h 34m 28s
Dec: −39° 04′ 9″

Con: Scorpius
Ch: MSA:1459, U2:408, SA:22

Ref: SIMBAD, SEDS

(reference key)

Type: globular cluster

Mag: B=?, V=11.5

Size: 3.6′
PA: ?

Historical observations

John Herschel (1847) Cape Observations

Discovered by Sir John Herschel at the Cape of Good Hope with an 18-inch f/13 speculum telescope. He recorded it as "a star 9th mag, with an eF nebulous wisp or tail, extending northwards about 1'." On a second occassion he called it "a star 9th mag with a very evident eF nebulous wisp 1.5' long, 30 arcseconds broad. (The wisp by the diagram is fan-shaped, and extends in the N.p. direction from the star. See fig 18, Pl VI.)"

NGC/IC Dreyer (1888, 1895, 1908)

The NGC records it as "extremely faint, pretty small, slightly elongated, 9th magnitude star attached." The cluster is also known as Pismis 25 and Ton 1. Its catalogued size is 3.9'.

Published comments

Helwan Obs. Bulletin No 9 (1912)

eF, S, a shapeless mass only just shown with an exposure of one hour; apparently not connected to star mag. 9 mentioned in NGC.

Burnham's Celestial Handbook

Burnham describes it as very small, extremely faint, diameter 2', stars of magnitude 16 and fainter with 8.5 magnitude star of southern edge.

Sulentic & Tifft (1973)

The RNGC (Sulentic and Tifft 1973) notes that this is a globular cluster.

Harris, W.E. (1997)

RA 17 34 28.0 (2000) Dec -39 04 09 Integrated V magnitude 11.31 Central surface brightness, V magnitudes per square arcsecond 19.96 Integrated spectral type Central concentration, c = log(r_total/r_core); a 'c' denotes a core-collapsed cluster 1.55c: Core radius in arcmin .34. ["Catalog Of Parameters For Milky Way Globular Clusters", compiled by William E. Harris, McMaster University. (Revised: May 15, 1997; from http://www.physics.mcmaster.ca/Globular.html; Harris, W.E. 1996, AJ, 112, 1487) ]

Meketa, J. (1984)

See Sky&Telescope, July, 1984, p88: "NGC 6380: An elusive globular cluster." by James Meketa.

Photo index

Photo Index by Jim Lucyk: Observer's Guide (Astro Cards) 5-6/88 p32.

Modern observations

[amastro] posting: A Weekend for Armchair Astronomy

Tom Polakis:

Barbara Wilson's globular cluster report was great reading. The globulars near the galaxy's center are well placed for the next dark run.

UKS-1 may be completely out of my league, as I use a 20-inch telescope. I did take a look at a few other faint ones that are nearby two weekends ago. A group of us were set up at Sunglow Ranch in southeast Arizona. This is a site that one member of this list says is about a half magnitude better than Prude Ranch. On a night with outstanding seeing and transparency,

Chris Schur and I looked at the once challenging globular NGC 6380. By Barbara's standards, this would be rather pedestrian, but I could see it being a challenge for a 10-inch or smaller scope. A half degree away is Ton 2, which really is a poor excuse for a globular cluster. It was nothing more than a faint mist 2' across with no central brightening through our 20-inch scopes. Again, it would be interesting to learn of the smallest scope used to see this globular. Being obsessed with little planetaries, Chris turned to Minkowski 1-27, which acts as a guidepost to globular Djorgovski 1. He didn't see it. I didn't see it. What were we doing wrong? Its size is listed in Megastar as a whopping 13.6' with a source given as "Skiff." I presume this size is a mistake, as Brian's table of globulars at http://www.ngcic.com/papers/gcdata.htm says the

magnitude is an uncertain 13.6, and gives no size. What's the real scoop on Djorg 1?

-----

Brian Skiff:

I observed NGC 6380 with my 15cm refractor from Las Campanas in Chile; Hartung also comments that it was visible in 20cm and 15cm aperture. So its evidently faint but straightforward from the southern hemisphere for modest apertures. The next step would be to resolve it, which should be possible with 35cm or 40cm at high power in good seeing (about like NGC 2419 in terms of brightest stars).

Both Roger Sinnott (for the MSA atlas) and Emil Bonanno (for MegaStar) seem to have got mixed up occasionally on the columns of my globular clusters "observables" table. It could well be that some tab characters slipped into the file (which I try to avoid) that were misread by software (and not checked by hand afterwards). At any rate, Djorgovski 1 is indeed mag. 13 or 14-ish and not 13.whatever arcminutes across. There is a paper by Ortolani et al (1995 A&A 296,680) that gives what I think of as an attempt at getting a color-magnitude diagram for the cluster. The brightest stars are _possibly_ as bright as V=18.5, but even if you believe the data apply to cluster stars (I'm not convinced), they have V-I color between 3.5 and 4.0, making them appear most of a magnitude fainter visually. The I-band image of the cluster shown in the paper barely reveals the cluster, and it would be several magnitudes fainter in V.

The current version of the globulars data table can be found at: ftp://ftp.lowell.edu/pub/bas/deepsky/globulars.tab A data is given at the top of the file showing when it was last revised.

\Brian

------------------------------------------------------------------------

Bob:

Tom,

N6380 is one of my favorite challenge globulars. George de Lange and I tackled it a number of years ago before it was fashionable to do so. We originally used the just released Uranometria 2000, but had no luck looking where it said it should be. I finally dug out a 1984 (June, I believe) issue of S&T which had an article on it as well as an astrophoto. Using the Astrophoto, we finally zeroed in on it. It was one of the lowest surface brightness globulars I had ever dug out, and there was an 8th or 9th magnitude star on the outer edge of the globular, making it very difficult to see. This was all back in the late 1980's and both George and I used our 16-inch Newtonians. One of the reasons I remember it so well is that at the time I was not expecting an NGC globular to be such a difficult object. Of all the NGC globulars I've observed, this one sure seems to be the faintest of them all.

/Bob

------------------------------------------------------------------------

[amastro] posting: discovery of NGC 6380

John Herschel, who discovered N6380 while at the Cape with his 18.75-inch,

refrained from describing it as a globular. Here are his two observations:

29 June 1834: A star 9m, with a very evident nebulous wisp 90" l; 30" br.

The wisp by the diagram is fan-shaped, and extends in the np direction from

the star.

10 July 1836: A star 9m, with an extremely F nebulous wisp or tail,

extending northwards about 1'.

Steve

[amastro] posting: NGC 6380 and M1-27

] From Brian Skiff --

] I observed NGC 6380 with my 15cm refractor from Las Campanas in Chile;

]Hartung also comments that it was visible in 20cm and 15cm aperture. So its

]evidently faint but straightforward from the southern hemisphere for modest

]apertures.

Wow. Shows what some added elevation will do. I'd have to describe N6380

as difficult with a 13-inch from my regular observing site in the Sierra

foothills (latitude 38.5 degrees).

To digress a bit, Tom mentioned using Minkowski 1-27 as a reference for

searching for Djorgovski 1. I'm curious if you tried blinking M1-27 with

an OIII or other filter? There seems to be little if any response.

Steve

[amastro] posting: Toughest NGC-globulars

] N6380 is one of my favorite challenge globulars. George de Lange and I

] tackled it a number of years ago before it was fashionable to do so. We

] originally used the just released Uranometria 2000, but had no luck looking

] where it said it should be. I finally dug out a 1984 (June, I believe)

] issue of S&T which had an article on it as well as an astrophoto. Using the

] Astrophoto, we finally zeroed in on it. It was one of the lowest surface

] brightness globulars I had ever dug out, and there was an 8th or 9th

] magnitude star on the outer edge of the globular, making it very difficult

] to see. This was all back in the late 1980's and both George and I used our

] 16-inch Newtonians. One of the reasons I remember it so well is that at the

] time I was not expecting an NGC globular to be such a difficult object. Of

] all the NGC globulars I've observed, this one sure seems to be the faintest

] of them all.

]

] /Bob

NGC6380 has also caused me trouble. I tried to view it from Western Australia in Nov 1997 when it was about to set (elevation 11 deg). Equipped with a 17".5 reflector, I tried to see the globular with powers between 71x -192x but I had to give up. It turned out that Uranometria plots the object at RA 17h35.4m whereas it should be at 17h34.5m. Every source that I have seen gives this wrong value in right ascension except MegaStar and Brent Archinals booklet about "Non-existent star clusters". There could be more. NGC6380 is also catalogued as Tonantzintla 1. The first entry in a list of only two globulars?! Ton 2 is situated only 0.6 deg to the NNE.

Last February, I tried again, knowing this discrepancy. Using the same telescope, NGC6380 was quite obvious once you knew where to look. The glare from the 9m star was disturbing. I could not discern any individual stars in NGC6380 but it was still quite low and I used only 125x. After this observation, I thought at first that I had finally hunted down every galactic NGC-globular. It turned out that NGC6540 in Sagittarius is nowadays classified as a globular cluster and I had omitted it from my list!

In my opinion, the toughest NGC-globular would be NGC6749 in Aquila. It has also wrong coordinates in many sources, has a low surface brightness and is in a rich star field. NGC7492 in Aquarius, NGC6426 in Ophiuchus and NGC1049 in the Fornax Dwarf are other NGC-toughies.

0.2 deg SE of NGC6380, there is a dark nebula called SL28. Has anybody seen it?

/Timo

------------------------------------------------------------------------

Timo Karhula "Amateur astronomers are * *

E-mail: atotika@ato.abb.se nocturnal creatures" * * *

ICBM: +59d52'13" +16d05'22"

----------------------------------------------------------- * *

Steve Coe

Steve Coe, observing with a 17.5" f/4.5 at 100X, notes: "Very, very faint, very small, not brighter in the middle, round at 165X. Appears like a double star at low power. At 220X it is 30" in size, round, and needs averted vision and good seeing to pick this very obscured globular out of the Milky Way. My friends and I are convinced that Wil Tirion included it on his Sky Atlas as a challenge object.; 36" f/5 TSP 96 7/10 S+T Not much with 36" of aperture, somewhat brighter middle. 6 stars resolved. "King of the little turd globulars".

Brian Skiff

Ton 1

Turner 1983: br *s SSE: V=6.77/0.25, V=7.28/1.25. wide pair on W: V=10.50, 12.77; 40"; pa5. br * nr center V=11.18; br * E V=11.40. pair SSE = ADS 5692: 6.6,10.6; 5".2; pa143; primary V=6.77, prob for both *s, implies V=6.8+10.8.

13cm - hazy patch just NE of two widely sep m6.5,7.5 *s that point to cl. three m12 *s stand out: one w/a fntr comp 50" N on W side; another nr center; last on E side. using averted vis about a doz threshold *s res, mostly btwn the two brtr *s. CBL, 5Feb1984, USNO.

25cm - mod f, lying NE of m6 *. 6' diam, 20 *s res m12+. a little concen. BS, 25Jan1982, Anderson Mesa.

30cm - rich, pretty cl of mostly f *s. 45 *s in 5'x3'.5 area elong E-W. no cen concen; in fact, around m12 * in center is 2'.5 hole w/only a few *s. most other members are in grps of two to five: three variously-oriented wide (15"-20") pairs are in W side. about a doz members are m13, the rest fntr. three m12 *s also. nrst br * SSE is a close un= pair (7.5,11.5; 5"; pa115). seeing deteriorating. CBL, 5Feb1984, USNO.

Contemporary observations

Auke Slotegraaf

1983

On one occassion, two observers using a 15.5-inch reflector at 220x could not find anything except a star of about magnitude 10.5.

Magda Streicher

(no date)

16-inch f/10 SCT (127x, 290x)

Very faint smutch of light seen with averted vision. Faint field stars forming a sort of cup shape grouping to the south. A 9Magnitude star come and go towards the south of the nebula.

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