Keyhole Nebula with Eta Carinae / Homunculus Nebula Inset (Anna Grunseth)

Keyhole Nebula with Eta Carinae / Homunculus Nebula Inset

After 3 months of careful imaging, experimentation, and processing, I'm sharing these multi-level views of the Carina Nebula, Keyhole Nebula, and the fascinating star Eta Carinae. This image is of the Keyhole Nebula region, centering on Eta Carinae — which “erupted” in the mid-1800s and has grown brighter ever since. Eta Carinae ejected a bulbous shell of stellar material, which is why it has an oblong shape. It’s sometimes hard to get a sense of scale in nebula photos, so I constructed some textbook-style inset images to show the relationship between these images. The highlighted areas in these diagrams are to proper scale.

These images were obtained on iTelescope.net T59 (Siding Spring Observatory, Australia, for the Keyhole Nebula region), and T72 (Deep Sky Chile, for the Keyhole and Eta Carinae images).

Keyhole Nebula:
Ha: 14x 300s
OIII: 18x 300s
SII: 17x 300s
R/G/B: 6x 60s each (stars only)
4hr 23m total

Planewave CDK 20” reflectors

Eta Carinae / Homunculus Nebula:
SII (->red): 41x 5s
OIII (->green): 18x 5s
Photometric U (->blue): 21x 5s
(This is the best half the data I collected, with many short exposures because the star is so bright)

I used narrowband and photometric filters to image this star so I could highlight details in different parts of its emission spectra. I mapped these to RGB channels to show a color image.
Eta Carinae is an extremely difficult object to image from Earth (unless you’re using a huge research-grade telescope). The details you see here are the result of me pushing the boundaries of iTelescope’s highest-resolution system (20” CDK, 0.359”/px), some great luck with outstanding atmospheric conditions in Chile (measured as 0.28”-0.48” seeing!), and an intensive data analysis and processing workflow that pulled as much detail out as possible (using PixInsight for data analysis and drizzle integration).

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