#astronomy In Heaven with M7, a Portal Into the Deep – Sky & Telescope
M7 in Scorpius is without doubt one of the brightest star clusters within the sky. Outlying stars body its jewel-like core, whereas darkish nebulae riddle all the area. North is up. Thomas Jäger / CC BY-SA four.zero I reside at latitude 47° north and actually haven’t any enterprise speaking about M 7 within the tail
M7 in Scorpius is without doubt one of the brightest star clusters within the sky. Outlying stars body its jewel-like core, whereas darkish nebulae riddle all the area. North is up.
Thomas Jäger / CC BY-SA four.zero
I reside at latitude 47° north and actually haven’t any enterprise speaking about M 7 within the tail of Scorpius. With a declination of –34.eight° it stands simply eight.2° above the southern horizon at end result. Regardless of this reality, the star cluster is routinely seen with the bare eye as a spherical powder puff of sunshine with a brighter heart. My view could also be compromised, however I am not complaining.
In 10×50 binoculars M7 is an incredible sight, with a packed, X-shaped core surrounded by vivid outliers that convey the full diameter to 75′. The cluster’s true extent is rather less than 25 light-years, and it is situated 990 light-years away within the Orion Arm of the Milky Manner. If an orb spider spun stars as an alternative of silk that is what its internet would appear to be.
Ptolemy was right here
M7 is often known as Ptolemy’s Cluster after the Greco-Roman astronomer Claudius Ptolemaeus who first recorded it as “a nebula following the sting of Scorpius” in AD 130. The cluster is a comparatively youthful addition to the galaxy with an estimated age of round 200 million years.
From my observing web site in northern Minnesota M7 by no means will get far above the treetops, but it is readily seen with the bare eye at magnitude three.three. Eighty stars reside there.
Due to its low altitude at my location, M7 is drastically affected by atmospheric seeing, which bloats and smears the celebs to various levels. I stick with low magnification (64×) with the 15-inch reflector on most nights. The blazing core suns pop like flashbulbs at a press convention, however my favourite characteristic here’s a 9 arc-minute-long chain of considerably fainter stars — magnitudes from 7.5 to 10.5 — that snakes east of the middle. Stellar pairs and triads additionally dot the sphere.
M7 is simple to search out four.9° east-northeast of Shaula and Lesath, the “Stinger Stars” within the tail of Scorpius. M7 culminates round 11:30 p.m. native daylight time in mid-July.
As eye-catching as M7 is, it additionally serves as a jumping-off level for different journeys. Inside and alongside its borders are a half-dozen extra deep-sky sights which occur to lie alongside the identical line of sight because the cluster. Let’s discover them.
Peeling again the layers
Globular cluster NGC 6453 (magnitude 10.2, diameter 7.6′) — I see a bit of ball of haze with a reasonably compressed core at 64× magnification alongside M7’s western border. It is not significantly vivid however straightforward sufficient to search out. Rising the magnification first to 142× after which to 245× I used to be fortunately shocked to see quite a few faint stars (~14th magnitude) resolved within the cluster’s halo. The globular seems fairly a bit smaller than its official diameter, nearer to 2′ by my estimate. A brighter star, presumably a member, lies alongside the cluster’s west-southwest edge.
Though in the identical line of sight as M7, NGC 6453 is far more distant — about 37,000 light-years away however simply three,260 light-years from the galactic heart. Intervening cosmic mud dims its gentle.
NASA / ESA / HST
Open cluster NGC 6444 (magnitude ~10.zero, diameter 12′) — What a curious form. Fifty suns of 11th magnitude and fainter kind a clumpy bar 12′ lengthy prolonged east to west that look as if somebody spilled them from a carried sack. With average magnification (142×) the view is wealthy with minute diamonds. Very good!
Open cluster Trumpler 30 (magnitude eight.eight, diameter 20′) — Though solely 20 stars are listed as members, this enticing, compact gathering appears to own twice that quantity. The sphere right here is so wealthy it is generally troublesome to visually decide what belongs to a cluster and what does not. Tr 30 stands out nicely, and its quiet sparkle makes a beautiful distinction to M7’s vivid splash.
Annie Leap Cannon was right here, too
This map plots the featured objects on our deep dive into M7. North is up.
Stellarium with additions by the writer
Planetary nebula Cannon 2-1 (magnitude 12.2, diameter 2″) — Abbreviated Cn 2-1, it appears precisely like a dim star though a couple of magnitude fainter than the listed brightness, most probably as a consequence of atmospheric extinction. Positioned 20,125 light-years away, the tiny nebula actually shines with an O III or UHC filter. In case you interpose the filter between your eye and the eyepiece the planetary will seem to brighten by about two magnitudes. Transferring the filter out and in of view will make Cn 2-1 flash and fade like a strobe gentle. It is also a helpful strategy to shortly establish it in a busy area.
This nebula was first studied by American astronomer and Harvard Pc Annie Leap Cannon, who’s greatest recognized for devising the OBAFGKM spectral classification nonetheless in use right now. She found a number of planetary nebulae whereas manually classifying about 350,000 stars.
On this south-up view, B287 appears prehistoric. The Interstellarum atlas mislabels the nebula as B286.
Darkish nebula Barnard 287 (25′ x 15′) — Chocolaty clouds of interstellar mud abound in M7’s neighborhood. In deep pictures with south up, B 286’s form resembles a pterodactyl in flight, however the most effective I may do at 64× was a imprecise, darkish presence bounded by an isosceles triangle of Seventh- and Eighth-magnitude stars. Jiggling the telescope to extend its visibility, I may see that the nebula’s western finish was darker, wider, and extra apparent that the remaining. You may discover this shadowy reptile 25′south-southeast of the cluster’s heart.
A deep photograph of M7 exhibits the entire featured deep-sky targets.
Mira variable SY Scorpii (magnitude vary eight.5 to 14.5:) — Fortunate us! This pulsating purple big with a interval of 234.9 days is at present at most. It lies throughout the boundary of the cluster 25′ north of the middle. Remember that an unrelated 10th-magnitude star shines ~15″ instantly northeast of the variable, giving the 2 the looks of a double star. I noticed SY on July 9.2 UT at magnitude eight.9, when its orange-red coloration was very obvious. Click on right here for an AAVSO star chart to find and comply with the star’s ups-and-downs. Cannon found SY Sco, too! It is one in all about 300 variable stars she unearthed.
I can solely think about how a lot better the view of M7 have to be from the Caribbean . . . to not point out the additional benefit of with the ability to stand as much as observe it as an alternative of crouching on one’s knees!