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NGC 2237 - Rosette Nebula

27 December 2024-1 January 2025

Jubera
- TS Optics Photoline 115
- Moravian C3-61000
(More info later in technical sheet)

Located about 5200 light-years from Earth and with a diameter of 130 light-years, Rosette is a type H II nebula, its light being due to the excitation of atoms by the radiation of the young stars inside it. Its shape resembles a rose, and is located in the constellation of Monoceros. The open cluster NGC 2244 (Caldwell 50) located in its center has formed from the material of the nebula itself. There is a lot of star formation going on within the nebula.

The image shown here corresponds to the days when we carried out observations in Jubera, between December 27, 2024 and January 1, 2025, being a very fruitful period due to the fantastic sky and weather conditions (see M42 - 2024 here.)

TECHNICAL INFORMATION

Location        Jubera (Soria), Coord.=41.20170, -2.36595, Alt.=933 
                SQM=21.84 mag/arsec2 Bortle=Class 3
Main Tube       TS Optics Photoline 115 mm f/7 EDT Triplet Apo. 
                Flat 0.79x, F.L. eff. 632 f/5.5
Guider Tube     Homemade ThorLabs 2" tube assembly 
                F.L. eff. 200 f/4
Main camera     Moravian C3-61000, 9576 x 6388, 3.76 µm
Guider Camera   ZWO ASI290MM Mini, 1936 x 1096, 2.9 µm
Mount           iOptron GEM45
Filters
   R    Broad Band nm Δ= nm  1x1, 2800 gain, T=-25oC, 30s x 15
   G    Broad Band nm Δ= nm  1x1, 2800 gain, T=-25oC, 30s x 15
   B    Broad Band nm Δ= nm  1x1, 2800 gain, T=-25oC, 30s x 15
   L    Broad Band nm Δ= nm  1x1, 2800 gain, T=-25oC, 30s x 51
   Hα   656.3 nm Δ=6.5 nm    1x1, 2800 gain, T=-25oC, 60s x 75
   Hα   656.3 nm Δ=6.5 nm    1x1, 2800 gain, T=-25oC, 120s x 39
   SII  670 nm Δ=6.5 nm      1x1, 2800 gain, T=-25oC, 60s x 60
   SII  670 nm Δ=6.5 nm      1x1, 2800 gain, T=-25oC, 120s x 22
   OIII 500 nm Δ=6.5 nm      1x1, 2800 gain, T=-25oC, 60s x 75
   OIII 500 nm Δ=6.5 nm      1x1, 2800 gain, T=-25oC, 120s x 38

Processing info

This picture has been processed in a similar way as in the case of M42 - 2024 (link here.) It is interesting to note that many of the photographs that can be found on the WEB (very high quality, by the way) taken with the so-called Hubble palette (Hα, SII and OIII narrow band filters), present very pronounced blue tones in the center of the nebula. This is due to the way in which the shots of each filter are integrated in the RGB channels. When done in the HSO order (Hα to R, SII to G and OIII to B), the color is altered, and although the effect is more aesthetic, it is less realistic. As we always say, anyway, to really see where each gas is, it is best to see the individual stacks of each filter.

In the following image strip you can see the relative intensity of the Hα, SII and OIII signals from Rosetta, when their stacked images are stretched exactly the same amount (although this is not ideal, since you would also have to take into account the sensor response, absorption in the atmosphere and in the telescope tube, etc., all of which is wavelength-dependent, as explained in our article here.).

Zoom As you can see, if we put the SII signal in channel G, its relative contribution is small, however, the OIII signal put in channel B greatly accentuates the signal in this channel, when in fact, OIII should contribute only 34% to the blue, and its RGB is (0.255.146). A non-proportional stretching of the three signals leads indeed to intense blues in the central region, which produce the typical HSO combinations of the Hubble palette. However, if we put everything in its place, based on the wavelength to RGB mapping, the result will be a slightly violet central region, as seen in our Rosette image.

You can find more info about NGC 2237 in wikipedia, as well as in NASA page here.

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