Lightning on Earth
17.07.2000

Nobody knows what causes lightning. It is known that charges slowly separate in some clouds causing rapid electrical discharges (lightning), but how electrical charges get separated in clouds remains a topic of much research.

The Pipe Dark Nebula
28.05.1996

The dark nebula predominant at the lower left of the above photograph is known as the Pipe Nebula. The dark clouds, suggestively shaped like smoke rising from a pipe, are caused by absorption of background starlight by dust.

In the Center of NGC 604
5.03.1997

Stars are sometimes born in the midst of chaos. About 3 million years ago in the nearby galaxy M33, a large cloud of gas spawned dense internal knots which gravitationally collapsed to form stars. But NGC 604 was so large, it could form enough stars to make a globular cluster.

The Veins of Heaven
19.06.2020

Transfusing sunlight through a darkened sky, this beautiful display of noctilucent clouds was captured earlier this week, reflected in calm waters from Nykobing Mors, Denmark. From the edge of space, about 80 kilometers above...

Plane Contrail and Sun Halo
4.04.2017

What's happened to the sky? Several common features of the daytime sky are interacting in uncommon ways. First, well behind the silhouetted hills, is the typically bright Sun. In front...

The Pipe Dark Nebula
21.06.1997

The dark nebula predominant at the lower left of the above photograph is known as the Pipe Nebula. The dark clouds, suggestively shaped like smoke rising from a pipe, are caused by absorption of background starlight by dust.

The Pipe Dark Nebula
5.03.2000

The dark nebula predominant at the lower left of the above photograph is known as the Pipe Nebula. The dark clouds, suggestively shaped like smoke rising from a pipe, are caused by absorption of background starlight by dust.

A Circumhorizontal Arc Over Ohio
19.05.2019

Why would clouds appear to be different colors? The reason here is that ice crystals in distant cirrus clouds are acting like little floating prisms. Sometimes known as a fire rainbow for its flame-like appearance, a circumhorizon arc lies parallel to the horizon.

Crepuscular Rays Over Utah
31.08.2005

What could cause such rays of dark? Dark sky rays were caught in spectacular fashion earlier this month above Utah, USA. The cause is something surprisingly familiar: shadows. Clouds near the horizon can block sunlight from reflecting off air, making columns outward from the Sun appear unusually dark.

Antares and Rho Ophiuchi
9.05.2004

Why is the sky near Antares and Rho Ophiuchi so colorful? The colors result from a mixture of objects and processes. Fine dust illuminated from the front by starlight produces blue reflection nebulae. Gaseous clouds whose atoms are excited by ultraviolet starlight produce reddish emission nebulae. Backlit dust clouds block starlight and so appear dark.