Cepheus to Cassiopeia
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Cepheus to Cassiopeia is an absolutely gargantuan image spanning across huge swaths of our home galaxy, showing many different narrowband nebula that are very faint and rarely imaged together. This large image which covers several hundred times the size of the full moon provides context on how these different faint nebula interact with eachother.
This image is a 35 panel mosaic captured in SHO narrowband, and it contains a huge number of the very faint emission nebulae which populate this part of the northern milky way. There is the flying bat nebula, the squid nebula, the elephant trunk nebula, the wizard nebula, the bubble nebula, the lobster claw nebula, the cave nebula, the question mark nebula, the ghost of Cassiopeia, and the pacman nebula to name a few. This image required over 80 hours of exposure to produce, which took place over three consecutive weeks. This image is more of a galaxy image than it is a nebula image, because it does more to illustrate the interactions of many nebulae at once. It is also worth noting that these objects are rarely ever imaged together, since many of them are very faint.
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Capturing this image presents two strong challenges, managing gradients and field rotation. Firstly for the gradient problem, I chose to capture every pane of the mosaic every night in a manner that is time and spacially coherent to minimize gradients and nonlinearities larger than a single image field. This means that horizon glow gradients are continuous, and variable seeing conditions are averaged in every panel to create a seamless image in the end. The other problem is that this section of the milky way is very far north, and due to the geometry of imaging in an equatorial coordinate system every panel of the mosaic will rotate by large amounts the closer you get to the pole. This is bad because it would force you to crop and lose imaging area. Since my setup has a field rotator I chose to image every single panel with a field rotation such that the final image would be a rectangle, maximizing my FOV. Some panels had to be rotated as much as 30 degrees relative to horizontal due to the polar effect.
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Exposure details per panel:
-9*300s Ha
-9*300s Oiii
-9x300s Sii
-60*300s Oiii for the squid nebula
Total exposure: 83hrs 55min