NASA's picture of the day, September 2: The beautiful Horsehead and Flame Nebulae glow in the Orion constellation

The Horsehead and Flame Nebulas (Image: NASA/Daniel Stern)

The night sky is full of shapes that evoke human awe. Among them, the Horsehead Nebula remains a favourite. Astronomers say this dark cloud resembles a horse’s head only by chance.

The Horsehead Nebula is one of the sky’s best known. It sits in the Orion constellation, glowing near other star fields. The dark horse-shaped figure is actually a dust cloud. It blocks the light of the brighter emission nebula.

Why does it appear dark in images?
The feature looks dark because it is opaque. The dense dust cloud lies in front of glowing gas. It prevents background light from reaching Earth-based telescopes. The shape is not permanent, scientists add.

The horse-like form will not last forever. Internal cloud movements will slowly distort its striking appearance. Experts believe changes will be visible after many millennia.

What gives the nebula its orange colour?
The orange color of the nebula is caused by recombining hydrogen atoms. Electrons and protons combine, creating the warm-hued emission. This process gives the cloud its distinctive fiery look.

Towards the lower left lies the Flame Nebula. It glows with a similar orange tint in images. Intricate dust filaments add depth to its bright structure. The Flame is another highlight of this cosmic neighbourhood.