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Narrowband

Just another observation of M71


Israel Sevilla

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A new object report observed with my dob 18" from this summer of 2022.

If you prefer to read it in PDF format with the support of some images that helps me to explain better myself you can check it in the web:

 https://theferretofcomets.com/index.php/en/messier-catalog/

Please take into account those images are pictures not sketches. As you can read in my web they have been gathered from public databases, mainly from telescopes in Palomar Mountain, HST and Calar Alto (Spain). What I have tried (quite successfully, I think) is to reflect how the object shifts with the change of eyepieces. The images can become a composite of several to show a better result. Also I have added a fixed rectangle to show the effect of the apparent field of the eyepiece. I play a little bit with the brightness and contrast to show how your eyepiece field is darker at lower eye pupil, but you lose details in the object. I mean, if you try to find exactly the same picture in the web you are going to fail. It takes a couple of hours (sometimes more) to generate all the pictures to get the better result, plus an extra hour to write down my voice-notes.

Nagler 31mm (70x - 1º 10’ - 6.6mm). A very cute object. It is a globular cluster in a star-studded field, it is surprising how many stars are observed in the field itself. There is a brighter star almost at 12 o’clock that catch your attention. But, despite the multitude of stars in the field, the cluster stands out clearly. Yet I have to say that at this magnification it is still too small, not even a tenth of the eyepiece field. It is quite concentrated and has the typical spherical shape of globular clusters but with important arms extending from it. I mean, the roundest part of it is its central area, rather than its outer halo, which extends unevenly into space with different arms of varying length. It has two levels of brightness although not very evident, being more concentrated and intense the central part, with a greater brightness than the outer arms that seem dimmer. Some stars can be resolved, not in the core of the cluster but in its outermost zone. Not many, I count about ten at most.

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Nagler 22mm (98x - 50’ - 4.7mm).  The view of the cluster is significantly improved and it is more beautiful with this eyepiece because it gains in presence. It has almost doubled in size, and although it is still small compared to the entire surrounding field, it is now easier to resolve the stars in the cluster and view it. I counted up to twenty individual stars in the cluster, reaching almost to the very core of the globular cluster. The field is still spectacular with dozens of faint stars chaotically distributed. Undoubtedly the most beautiful part of the cluster is its innermost one and, with this eyepiece, the arms are much more clearly distinguishable and appear more independent of the cluster itself. It is as if the cluster were actually a sphere of stars surrounded by several stars of similar magnitude but without being connected to the core. Something like a cloud of stars surrounding the cluster. This clear separation between stars of its outer halo and the core gives it a more beautiful appearance, because you can focus your eyes on these stars to find a different shape to the cluster. To me it looks like a kind of arrow because there is a series of stars to its six o’clock of which to the right and left there is none. Or maybe it is a kind of comet, with a tail. I like it, because the surrounding field in the Milky Way is spectacular. And although it does not seem an impressive cluster to the eye, the balance in brightness between the outermost and innermost part, and its concentrated size makes it very beautiful to observe.

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Delos 14mm (154x - 28’ - 3mm).  With the 14mm the cluster is easily resolvable and becomes much larger, occupying almost a quarter of the eyepiece. However, I lose that wonderful starry field that used to surround it, and it has also lost some of the cohesion that it showed at lower magnification. Now even in the very core the stars can be counted individually. Fifteen I can count easily, and twenty if I try a little harder. The outer arms have ceased to be so to become that cloud of stars that chaotically surround the cluster. Nor is this aspect so negative since, not being part of a specific grouping, one can look at the individual stars to enjoy them. For example at six o'clock there are two very close stars that attract attention, also at three o'clock and at eleven o'clock there are a little brighter stars delimiting what would be the core of the cluster. The minutes pass peacefully while you contemplate carefully what signs can serve to delimit the most central part of the cluster.

A delight.

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Ethos 10mm (216x - 27’ - 2.1mm). In my opinion, this object really appreciates the added magnification. The brightness of the cluster has almost not diminished and now we can distinguish much more space between the different stars and observe them with more attention. I can not provide much more information than already described in the previous paragraphs because I do not discover any new feature that catches my attention, however I keep adding magnification because it is a pleasure to observe the same object from different magnitudes because the aspect it shows is different.

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Ethos 8mm (270x -  22’ - 1.7mm). The 8mm Ethos has not given me a better view. The cluster is a little larger but there is no significant difference to the previous eyepiece.

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Delos 4.5mm (480x - 9’ - 1mm). Although the magnifications are very high, it is worthwhile to reach them because the image of the cluster changes quite a lot. Just as between 10mm and 8mm it seemed that the object did not show any difference, the jump to 4.5mm has given me a different view. Now it is difficult to see it as a globular cluster because its shape is no longer round, and the stars are very clearly differentiated. There are several double stars with very similar brightness, specially two pairs at 6 o'clock and in the interior of the cluster, stand out. In previous eyepieces there was always a sort of fainter cloudiness surrounding the cluster from the lower brightness stars that were not resolved. That faint glow has disappeared in this eyepiece and the object looks much easier to analyze as individual stars. So your idea of it changes in a way that almost makes you wonder if you are looking at the same object. Just seeing the same bright stars in the same places and similar structure is what confirms that you are seeing the same cluster but it is a very significant change. Despite not having much detail, the surrounding field at low magnification and the ease of resolving stars of significant magnitude in itself makes it an interesting object to observe.

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Clear and dark skies, Israel

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