Skyguide - Selected objects for every season
The Skyguide is primarily intended to give suggestions for your own observations and will briefly describe selected objects for each season of the year. Both easy and difficult objects will be selected. How difficult an object is depends of course on several factors, especially sky quality, telescope aperture and experience of the observer.
For each object the most important information is given in short form. These are supplemented by photos or sketches. Furthermore, a map, created with the free software Cartes du Ciel (Skychart), is available for a rough orientation. In general, I recommend, to create your own finder charts. The visual description of the object is based mainly on own observations and should serve only as a starting point.
Skyguide 2024-2 (Summer)
The moderately conspicuous, extended constellation Ophiuchus lies between Hercules in the north and Scorpius in the south. Ophiuchus is probably best known for its globular clusters. In addition to Sagittarius to the southeast, it contains 7 globular clusters, the most of this type in the Messier catalog, which includes a total of 29 globular clusters. They can all be easily observed with binoculars. Messier 10 and Messier 12 are particularly worthwhile, which still fit well into the field of view of low magnification binoculars with an angular separation of just under 3.5 degrees. Messier 14, located further east, is noticeably fainter and less condensed in direct comparison.
A somewhat fainter globular cluster is Messier 9 in the south-eastern part of the constellation. A small pair of binoculars is sufficient for sighting it under dark skies. To see the first individual stars, you need at least a telescope with an aperture of about 200 mm, whereby the center appears very compact. Photographs and sketches sometimes show a “dark band” on the north-western edge. Here the globular cluster is attenuated by interstellar matter. This sometimes gives the impression that the globular cluster does not appear completely round. Under what conditions can this dark band be seen or at least guessed?
Let us now move eastwards into the constellation Sagittarius, where the globular cluster NGC 6440 and the planetary nebula NGC 6445 are located. The angular distance between the two objects is less than 30 arcminutes, so both objects can be observed together. NGC 6440 appears as a rather faint, compact nebula in smaller telescopes. At what aperture are individual stars visible? The planetary nebula NGC 6445, on the other hand, offers some details even in medium-sized telescopes. Due to its rectangular shape, it can also be found under the name “Box Nebula”. It is similar to the Small Dumbbell Nebula (Messier 76). In a small telescope, it can only be seen as a small nebula. Visibility can be made easier with nebula filters. The nebula is characterized by a brighter edge, while its interior appears darker. Faint, irregular filaments of the nebula can still be seen in photographs. Can these also be detected visually?
The last object we would like to present is the planetary nebula Minkowski 2-9 (Butterfly Nebula, Twin Jet Nebula). Like the Egg Nebula (PK 80-6.1), it is a bipolar nebula with an extraordinary structure. This gives it an elongated appearance. Although it can be easily observed with medium-sized telescopes, it was first discovered in 1947 by the German-American astronomer Rudolph Minkowski. Its small angular size requires high magnifications. In a telescope with 320 mm aperture, the nebula looks like a blurred, elongated star at a magnification of 72x. The bipolar structure becomes clear at a magnification of around 200x. Nebula filters help with identification. The brightness of the central star is given as mv = 15m.7.
If you prefer it brighter and larger, move back to Sagittarius, where you will find objects such as Messier 8 (Lagoon Nebula), Messier 17 (Swan Nebula) and some open clusters. Binoculars will certainly provide a nice overview of this rewarding region.