Milky Way from Monoceros to Gemini

On this page a 21°×40° wide-field view of the Milky Way in the constellations Monoceros, Orion and Gemini is presented. That part of the sky is full of HII regions, but there are only a few reflection nebulae.

All pictures below are downscaled versions. Full resolution images with more than 100 megapixels can be loaded with a Javascript viewer by clicking on the images in the first section. Selected details are shown in the second section. The third section presents some discoveries. Image and instrument data can be found at the end of this page.

Full views

Click on the images to load a full resolution version with more than 100 megapixels using a JavaScript viewer.

Milky Way from Monoceros to Gemini in H-alpha (red), blue continuum (green) and red continuum (blue) — This image is a false color composite in which H-alpha (including red continuum) is mapped to red, blue continuum (including [OIII] and H-beta emissions) is mapped to green, and red continuum (without H-alpha) is mapped to blue. Reflection nebulae appear green to blue, while HII regions are red. Stars in the continuum channels are partially subtracted to make the faint nebulae visible.

Milky Way from Monoceros to Gemini in H-alpha (false color) — This visualization is a pseudo-color image that only uses the H-alpha data (including some red continuum). It shows many more details of the emission nebulae than the image above.

**Color composition:** After partial star subtraction, the dynamic range was compressed using a non-linear high-pass filter. This results in a compression ratio r, which is used to calculate the color as depicted in the legend. (The legend shows the compression c:=1-r). Blue regions are compressed the least, while white regions are compressed the most. Luminance is determined by the tonal curve-corrected result of the dynamic range compression.

Legend for false color image of Milky Way from Taurus to Perseus in H-alpha — This visualization is a pseudo-color image that only uses the H-alpha data (including some red continuum). It shows many more details of the emission nebulae than the image above.

**Color composition:** After partial star subtraction, the dynamic range was compressed using a non-linear high-pass filter. This results in a compression ratio r, which is used to calculate the color as depicted in the legend. (The legend shows the compression c:=1-r). Blue regions are compressed the least, while white regions are compressed the most. Luminance is determined by the tonal curve-corrected result of the dynamic range compression.

Milky Way from Monoceros to Gemini region in RGB — An almost-true color image. Unlike to the other images, the stars are not subtracted. This improves the visibility of dark nebulae that absorb the light from the stars behind.

Due to the limited resolution of continuum channels, the image is only presented at half resolution.

Selected details

Here are a few details that also can be seen using the JavaScript viewer.

NGC 2264, Rosette Nebula and IC 447 — Nebula complex containing NGC 2264 (SH2-273, with the Cone Nebulae) and the Rosette Nebula (SH2-275). The turquoise reflection nebula is IC 447.

NGC 2264, Rosette Nebula and IC 447 in false colors made from H-Alpha — Same view as above, but here as pseudo color composite from H-alpha data.

SH2-249 (IC 444), Jellyfish Nebulae (SH2-248, IC 443), Monkey Head Nebula (NGC 2174, SH2-252) — The three largest nebulae from top left to bottom right are: SH2-249 (IC 444), next to it: Jellyfish Nebula (SH2-248, IC 443, a supernova remnant) and the Monkey Head Nebula (NGC 2174, SH2-252).

Orion region: Detail of Barnards loop — Thor's Helmet (NGC 2359, SH2-298, the small structure in the lower left quarter) and a large HII region that contains the Seagull Nebula (the center part of the large structure across the whole image). Also see the discoveries.

Discoveries

The views above show many nebulae that cannot be found in catalogs. (The JavaScript Viewer allows identifying objects using catalogs or SIMBAD and defining new objects.) Some (probably not all) of these unexplored nebulae have been collected in the list below. Click on the following links for a presentation.

Objects that are not cataloged by now and objects the are related to them (the list does not contain objects that are only minor extensions of known structures):
- F2-F9, FA1-FA6 in H-alpha
- F2-F11, FA1-FA6 in H-alpha and Continuum
HII region, labelled F1, which contains the Seagull Nebula (at least the body) and various other emission Nebula, at least SH2-295 to SH2-297. That region is ionized by the CMa OB1 association and it lies in a distance of about 1000pc (=3261 light years). It is unclear whether IC 2177 (the head of the seagull) and SH2-293 belong to that nebula complex, because there are no usable parallax measurements for the ionizing stars. SH2-289 (Thor's Helmet) is about 5 times as far away as the nebula complex F1 and therefore does not belong to it.
Click on the link above to load a presentation with sources that can be used for distance measurement. Outlines of known nebulae can be plotted by pressing the '3' key of via the menu.

Notes

In the JavaScript viewer, the object outlines can be toggled on and off by pressing the '2' key. This can be helpful to make certain structures (e.g. rings) visible.
False color images containing H-alpha and continuum:
- H-alpha is mapped to red, blue continuum is mapped to green, and red continuum (without H-alpha) is mapped to blue.
- Color of molecular clouds and reflection nebulae in the false color image is something between green (bluish in reality) and blue (reddish in reality).
- HII regions (ionized hydrogen) appear red to orange, depending on the amount of OIII (doubly ionized oxygen) detected by the blue continuum filter.
SIMBAD queries for certain object types can be made easily in the JavaScript Viewer by drawing a circle and pressing a shortcut key or via the menu
A repository with the discoveries can also be found on GitHub

Image data

Images where captured with a camera array which is described on the instruments page.

Image data are:

Projection type:

Stereographic

Center position:

RA: 6h46, DEC: 5°

Orientation:

North is up (exactly)

Scale:

10 arcsec/pixel (in center at maximum resolution)

FOV:

30°×28° (RA×DEC, through center)

Exposure times:

Sum of exposure times of all frames used to calculate the image.

H-alpha:	8.1 d
Continuum channels:	4.7 d

Image processing

All image processing steps are deterministic, i.e. there was no manual retouching or any other kind of non-reproducible adjustment. The software which was used can be downloaded here.

Image processing steps where:

Bias correction, dark current subtraction, flatfield correction
Alignment and brightness calibration using stars from reference image
Stacking with masking unlikely values and background correction
Star subtraction
Denoising and deconvolution both components (stars and residual)
RGB-composition (same factor for stars and residual for the true color composite)
Dynamic range compression using non-linear high-pass filter
Tonal curve correction

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