L'ammasso globulare M 13 è sempre uno splendido soggetto astronomico e praticamente ogni astrofilo cerca di fotografarlo. Qui vediamo la ripresa fatta da Alessandro Di Giusto, nostro conoscente che lavora alla rivista Il Friuli. L'oggetto astronomico è prospetticamente posizionato nella costellazione di Ercole (Hercules - HER) ed è uno degli oggetto più belli del nostro cielo, sicuramente l'ammasso globulare più famoso e conosciuto, anche se altri globulari sono altrettanto belli. Essendo al limite della visibilità d'una persona dotata di buona vista, in condizioni di cielo sereno e buona trasparenza atmosferica (oltre che di assenza di inquinamento luminoso) si nota come una macchiolina indistinta situata nella parte destra della testa dell'eroe mitologico Ercole (dal quale ha preso il nome la costellazione).

Di seguito riporto i dati del nostro planetario Guide 8.0 per M 13

Commenti tratti dal Progetto NGC-IC:
Ammasso globulare
Tipo: V
Asc. retta: 16 41 41.5 (J2000)
Declinazione: +36 27 37
Magnitudine: 5.8
Asse maggiore: 23.20 minuti d'arco
Costellazione: HER
Designazioni alternative:
M 13 - GCL 45 - Hercules cluster
Asc. retta: 16h41m41.5s
Declinazione: +36 27' 36"

Note dal Catalogo NGC2000:
J2000 AR: 16h41.7m
J2000 dec: +36 28'
!! glob. cl. , eB, vRi, vgeCM, st 11...; = M13
NGC 6205: very much remarkable globular cluster, extremely bright, very rich in stars, very gradually extremely 
compressed middle, stars 11...; = M13 

Commenti dalle Osservazioni di Steve Coe:
NGC 6205 (M 13)  very bright, very large, little elongated, easily resolved at 100X. From a dark location this object 
just about exceeds the 20 min field of my 12 mm Erfle eyepiece.  This gives 165X on my 13" f/5.6 and this glorious 
cluster has streamers out from a blazing core in all directions.  Three dark, thin lanes can be seen cutting the 
core into unequal thirds, I have heard this feature called the "Propeller".  I believe this globular gets a lot of 
press for several reasons:  it is easy to find, it is one of  the finest globulars, it is easily resolved in small 
scopes and it comes overhead for the Northern Hemisphere.  Sir William Herschel estimated 14,000 stars in the cluster, 
some hardy soul at Mt. Wilson counted 30,000 on a plate from the 100" Hooker telescope in 1931.  Actually, there are 
about half a million stars in M 13. Wow. 
With the 13" at Cherry Rd. on a night with 6/10 seeing and 8/10 transparency, M13 is just seen naked eye, faint but 
there. It has about 1/2 the size of the Lagoon Nebula naked eye. In the 11X80 finder there are three layers of 
brightness, but the cluster is not resolved into stars.  At 100X it is very bright, very large, well resolved, much, 
much brighter in the middle and little elongated 1.2 X 1 in a PA of 90.  The most prominent chains are off the north 
and south sides with many silvery stars in front of a sparkling globe in the background.  Moving to 220X shows the best 
view with the 8.8mm Ultra Wide.  I counted 41 stars in the NW quadrant, most are silver, a few are yellow or light 
orange. 
The dark "propeller" is held with direct vision as small, thin dark lines.  There is a chain of 9 stars which run across 
the core from East to West.  At both 330X and 440X the silvery appearance of the brighter stars is gone, they are off 
white, but the dark lanes seem more prominent and these high powers show all the scope can provide in this grand cluster. 
Camp 613 S=8, T=10 Wow night.  Easy with naked eye, has size with no magnification, averted vision makes it larger.  In 
the 11X80 finder, three level of brightness, but no stars resolved.  60X-very bright, very rich, gradually extremely 
compressed middle, irregularly round.  This nice wide angle view shows the two approx. 7th mag stars that guard M-13 
and NGC 6207, a prominent galaxy to the north.  Going to 150X with the 14mm UWA resolved 63 stars in NE quadrant, the 
two most prominent curved chains of stars go to NW and SW.  The dark "Propellor" is seen on south side, has a faint 
double star in the western most dark lane. The beautiful silvery sheen of a bright globular is most prominent at this 
magnification.  440X-WOW!!  many, many faint pairs and groupings.  The Propellor is easy a complimentary dark lane now 
appears across the center of the cluster on the north side.  Averted vision really "fills in" the cluster with a myriad 
of faint member star.   A great night. 
Ultimate Star Party, McDonald Obs. Oct. 95, S=6, T=8, 36" f/5-- 
M 13 in 36" with 35mm Panoptic is as glorious as you might expect, hundreds of stars resolved with a fuzzy background 
of stars at the edge of resolution.  The Propeller, a dark three-vaned feature, is easy, it does not split the cluster 
into equal parts, put does stand out nicely.  Moving to Clyde Bone's 24" Naysmith folded telescope shows an excellent 
view of this object with many stars resolved and several curved chains of stars winding their out from the central mass 
of this globular.  Nice to sit down and be comfortable while observing.  
36" f/5 TSP 96 20mm Nagler.  Spectacular, 193 stars counted in NW quadrant.  Many, many beautiful chains, tendrils out 
from main ball of stars, many double and triples stars within the curved chains out from the ball in the middle.  The 
central globe of stars is obviously a round ball of stars, no doubt.  The dark "Propeller" feature is seen with direct 
vision, and is more prominent with averted vision.  I know this is a showpiece that gets observed every time scopes are 
set up in the Springtime, but this is all but a brand new view of it.  I had the feeling this was all that there was to 
see in M-13.  Going to a 14mm Meade UWA eyepiece shows off the Propeller better, more contrast.  There is another dark 
lane, across from the Propeller, that is also seen with direct vision.

Commenti tratti dal SAC (Saguaro Astronomy Club) 7.2:
NGC 6205
M  13
Tipo di oggetto: GLOCL
Costellazione: HER
Asc. retta: 16 41.7 (J2000)
Declinazione: +36 28
Dimensioni: 23.2
Classificazione: V
!!eB,vRi,vgeCM,*11...
Hercules cluster;Messier said round nebula contains no star

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