Hi all,
Yet again, the skies stayed hidden behind clouds for several nights, but tonight they finally cleared, giving me the chance to capture another mesmerising object: C4 ‘Iris’. Not the biggest object compared to larger nebulae or galaxies I’ve captured before, but still quite a blue beauty.
The Iris Nebula (Caldwell 4, NGC 7023) is a striking reflection nebula in the constellation Cepheus, about 1,400 light-years away. Its name comes from the blue, petal-like glow created as starlight from a young, hot central star scatters off surrounding dust. Unlike emission nebulae, which shine because gas is ionized, the Iris glows by reflection, making its colors softer and more delicate. Dark clouds of interstellar dust curl around its luminous center, giving it a dramatic contrast against the starry background and making it a rewarding target for astrophotographers.
As mentioned above, C4 ‘Iris’ is a reflection nebula, and not an emission nebula like all other nebulae I have been capturing so far. But’s what’s the difference?
The difference comes down to what makes the gas and dust visible.
A reflection nebula like the Iris shines because dust grains scatter and reflect the light of nearby stars. That’s why they often look blue—the same reason our sky is blue, since shorter blue wavelengths scatter more efficiently. The gas in these regions is too cool to glow on its own, so they act like cosmic mirrors.
An emission nebula, on the other hand, is lit from within. Hot, young stars pour out ultraviolet radiation, which excites the surrounding hydrogen gas. When the gas atoms calm back down, they emit their own light, usually in vivid red (the hydrogen-alpha line). Famous examples are the Orion Nebula (M42) and the Heart Nebula (IC 1805).
So reflection nebulae are like starlight bouncing off cosmic fog, while emission nebulae are like neon signs where the gas itself is glowing.
Because of its difference (where emissions nebulae are typically captured with the Duo-Band filter), capturing the beauty of Iris needs to be done with the Astro filter. This got me, but I quickly realised my mistake early in the session (Duo-Band filter selected), only loosing 10 minutes or so before restarting the capture with the Astro filter.
Here is 3 hours and 37 minutes at 60 seconds exposure, gain 60 and Astro filter:
Like I mentioned in one of my previous posts, my preference goes to capturing Nebulae, although I really love the images of the Pleiades (M45) too… must be the blue colour, and hence, the beautiful blue Iris is I think one of my favourites so far!
The Dwarflab Dwarf 3, in combination with the deep sky, an adventure that just keeps giving, and keeps amazing me!
To endless exploration, starry nights, and a little bit of cosmic nerdiness!
TTG
