Messier 45 is an open cluster in Taurus with an angular size of 110 arc minutes at a distance of 410 light years and an apparent aggregate magnitude of 1.2, it is one of the most obvious open clusters to the naked eye. It is relatively young open cluster of hot, bluish B-type stars with an estimated age of only 100 million years; its brightest member is Alcyone, eta Tauri, at magnitude 2.86, and it is classified as a Trumpler Type I 3 r open cluster. The ten brightest, named stars of the Pleiades, Alcyone (eta Tauri m. 2.86), Atlas (27 Tauri m. 3.62), Electra (17 Tauri m. 3.70), Maia (20 Tauri m. 3.86), Merope (23 Tauri m. 4.17), Taygeta (19 Tauri m. 4.29), Pleione (28 Tauri m. 5.09 var. as BU Tauri), Celaeno (16 Tauri m. 5.44), and the close pair Sterope/Asterope (21 & 22 Tauri, m. 5.64 and 6.41), are all brilliant blue stars of spectral class B6 through B9, concentrated in a field of just over one degree of arc which spans roughly 7 light years. Blue reflection nebulae with prominent filaments surround several of the brighter stars, particularly Merope, Alcyone, Maia and Electra.

The Pleiades are commonly known as the "Seven Sisters" as was depicted as a seven star pattern in Assyrian art work. A close examination shows, however only six stars brighter than magnitude 4.29, with another four stars ranging in magnitude from 5.09 to 5.66. The Greeks were aware of the presence of only six bright stars, and it is interesting to ponder why the Assyrians recorded seven.

Calibration with temperature-matched dark frames of identical exposure, along with sky flats and matched dark frames. Processed in Pixinsight as follows:

AutomaticBackgroundExtraction on separate RGB planes

PhotometricColorCalibration

MultiscaleLinearTransform of chrominance

MaskedStretch

MorphologicalTransformation with StarMask

TGVDenoise

CurvesTransformation



Cropped and converted to JPG for upload. Rotated to a North-up orientation.

The image is a two-pane mosaic assembled in Pixinsight using StarAlignment and Gradient Merge Mosaic.