The California Nebula (NGC 1499) in the Constellation Perseus is relatively close to us, about 1000 lightyears away in the Orion Arm of our galaxy (Milky Way), and it's roughly a 100 lightyears in length, so what you see here, top to bottom, is about 600 trillion miles of ionized hydrogen. NGC 1499 is a good-sized emission nebula, about 2.5° in length from our view on Earth. To put that into perspective, a full moon is 1/2°, so the California Nebula is about 5 full moons long in the sky.
Imaging session notes: 50 x 240 second subs, stacked in DSS, processed in PS 2021. SkyWatcher EQ6-R Pro mount, William Optics GT81 Apochromatic Refractor 392mm at f/4.7, ZWO ASI1600MM-Pro monochrome camera, Astronomik 6nm Ha filter, Controller: Raspberry Pi 4 4GB / 128GB running INDI/KStars/Ekos.