Learn
Background articles on the physics behind these images — with diagrams of the mechanism and figures taken from the gallery itself, where you can actually see it.
Learn · Fundamentals
Almost all the red in this gallery is a single spectral line of the most abundant element. What distinguishes H₂, H II and Hα, why molecular clouds are dark — and why the eye misses the red of the nebulae entirely.
Learn · Fundamentals
Only one percent of the mass between the stars, yet it draws every picture: dust swallows, reddens and mirrors light, builds the molecules of the stellar nurseries — and in the end the planets are made of its grains.
Learn · Nebula physics
Why emission nebulae carry glowing rims, pillars, and comet-like globules: a single mechanism explains the most striking shapes in the night sky — and it is there in almost every image in this gallery.
Learn · Stellar nurseries
From the dark cloud core through disk and jets to the finished cluster: why stars are never born alone, how their own radiation closes the factory and opens it again — and where in the Elephant's Trunk you can watch a freshly ignited star.
Learn · Stellar nurseries
The Orion Nebula is the nearest large star factory, visible to the naked eye and, since 1880, every astrophotographer's first subject — here on a rediscovered exposure from 2016, from this gallery's Newtonian era.
Learn · Stellar evolution
Same distance, same age, same chemistry: star clusters are the laboratories of astrophysics, and their turnoff point is a clock you can read. On open clusters that pass away, globular clusters that remain — and the lost siblings of the Sun.
Learn · Stellar evolution
Blue giants burn out in millions of years, red dwarfs live for trillions — and the Sun sits unspectacularly in the middle. How a single dial fixes a star's temperature, color, luminosity and manner of death.
Learn · Stellar evolution
More than ninety percent of all stars do not explode, they dissolve — and shine for a cosmic instant while doing so. On the Dumbbell M 27, the nebulium puzzle, hourglasses in the sky and the fate of the Sun.
Learn · Stellar physics
Only about 700 of these stars are known in the entire Milky Way: naked helium cores with winds of thousands of km/s. One of them stands in this gallery — and its ring nebula tells how a fast wind catches up with a slow one.
Learn · Stellar explosions
Core collapse or a detonating white dwarf: why there are two completely different kinds of supernova, what sets a nova apart from them, and how an explosion turns into the Veil Nebula 20,000 years later.
Learn · Other galaxies
The thin needle of NGC 891 and the open spiral of NGC 6946 look fundamentally different. How much of that is structure, how much perspective? On Hubble's tuning fork, bars, inclination angles and what colours can and cannot tell us.
Learn · Other galaxies
Galaxies grow through gas inflow and mergers, build disks, bars and black holes, and eventually stop forming stars. Why star formation in the universe passed its peak long ago — and what of all this is in our images.
Learn · Other galaxies
Bridges, tails, starbursts and shells: what happens in an encounter, why stars never collide in one, which scars the Milky Way and Andromeda carry — and why their own collision is by no means settled.
Learn · Other galaxies
Groups, clusters, superclusters, filaments and voids: how galaxies populate space, how their distance is measured at all — and why the small patches next to NGC 891 are eight times further away than the galaxy itself.
Learn · Galaxies
Andromeda and Triangulum are our large neighbours beyond the Milky Way. On the Local Group, spiral structure and a shared future whose outcome remains uncertain.
Learn · Solar System
The only object in this gallery with a visible landscape — and a lesson in light: at the terminator the Moon shows its relief, at full moon its material. On Theia, the maria, ray craters and the art of photographing against atmospheric turbulence.
Learn · Sky geometry
A photograph has no depth axis: stars in the middle of nebulae, clusters in front of dust walls, constellations as chance patterns. On the finest illusions in this gallery — and how astronomy measures the lost third dimension back.
Learn · Method
No eye sees a nebula like this — and still nothing is invented: why narrowband filters, hours of collecting and stretching show the colors of physics, what “false color” would really mean, and what the eye would see at the eyepiece.
Learn · Method
Between a nebula and its image lie a hundred disruptive kilometers of atmosphere — and a warm sensor. On seeing and the jet stream, dew on the clearest nights, the light dome, and a measurement of our own: +4.7% noise per kelvin.
Learn · Technology
Only a handful of photons per second arrive from a nebula — everything else follows from that: mount and guiding hold still, the cooling keeps quiet, and statistics build the one clean image out of many noisy frames.
Learn · Technique
At the Moon there is light in abundance and the atmosphere is the adversary — so you shoot video instead of exposing, and keep only the calmest moments. On seeing, Barlow lenses, planetary cameras, drizzle, and the diffraction limit that wins in the end.