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Messier45.com provides essential tools for the deep sky observer; the map, the lists of objects and observation projects.
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Deep Sky object types
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This list was compiled from an txt-file originally made by The Astronomical League in the US, consisting of the 400 best objects viewable from North America in William Herschel's 2514 entry long list of deep sky objects (originally compiled by Lucian Kemble, Canada).
Arild Moland adapted it to Norwegian latitude (58°N-72°N) by removing all entries below -25° in Declination and all (or most) objects in typical summer constellations like Sagittarius and Scorpius. These objects were replaced by other, presumably bright Herschel objects at magnitude 12 or brighter.
The 88 Constellations
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What is Messier 45?
The deep sky object Messier 45, number 45 on famous astronomer Charles Messier's list of clusters and nebulous objects, is a beautiful naked eye open cluster of mostly blue stars shrouded in dust reflecting the blue starlight, some of which is visible even in binoculars.
The cluster is also called The Seven Sisters, where the sisters are seven of the brightest stars in the cluster. The two bright stars to the left in the cluster are the parents, Atlas and Pleione, hence also the more common name Pleiades (the children of Pleione). The seven sisters are Alcyone, Merope, Electra, Maia, Celaeno, Taygeta and Asterope.
Open clusters are perfect for any telescope or binoculars, and they come in all shapes and sizes. Many are bright, but even the faint ones are accessible with modest equipment. The clusters are located mostly along the Milky Way plane, but some of the nearest clusters appear outside the plane of our galaxy.
Popular open cluster catalogs
Many of the clusters on these catalogs are some of the finest in the sky.
Deep Sky Hunters catalog
A group of amateurs have over some years collected a sizeable list of possible and definite clusters. Many are asterisms, and some of the objects found are even new planetary nebulae too! However the primary goal of the groups founder Bruno Alessi was to discover true open clusters. The work has also resulted in a published paper with a subset of the most promising cluster candidates.
These rich balls of stars are always wonderful to seek out and observe. Many are easy targets, while others are borderline open clusters or small or faint. Some of the brightest deep sky objects are globulars, but it's also possible to observe truly faint and tiny globulars in Andromeda or other neighbouring galaxies.
Perhaps the most beautiful objects of all are the planetary nebulae. These objects vary immensely in size, magnitude and colour, depending on their age, orientation, composition, etc. They are remnants from small to medium sized stars' final stance in it's battle against gravity.
Here are some suggestions to manageable (and possibly challenging) lists of PNe.
Bright nebulae come in many shapes and sizes. They can be tiny specks or stretch over an entire constellation. It's generally difficult to put a definite border to these illusive clouds and many "objects" in this database are merely parts of large regions of nebulosity. Although some small and clearly defined nebulae have a specified magnitude, most don't. For these it is often better to rely on the Sharpless or Lynds classifications to get an idea on how bright they are.
Popular Galaxy Catalogues
Galaxies in Galaxy Clusters
Area: sqr °