The Rhythm of the Spheres

Reading the Night Sky

Wandering in Astronomy

The night sky is the oldest pattern of man, and every culture reads it differently. The stars above keep silent time, moving to a rhythm we are just now beginning to understand. Astronomy is where math, science, art, music, and words meet in a wondrous collision. In this section of our site, learn the basics of astronomy: from how a star chart is made, to projections and art that map the night sky, to how an astrolabe works just like it did thousands of years ago. Watch the North Star shift across centuries, explore how one sky has been mapped by many traditions, read what happened on this day in space, and see tonight’s moon for your location.

Map the Stars

The math behind star charts, with a projection explorer and a working astrolabe.

The Moving Sky

How the sky shifts across centuries, with a precession clock you can run.

The Traditions

One sky reads many ways, with a same-sky overlay of the world’s constellations.

This Day in the Stars

The sky’s events, discoveries, and lore tied to today’s date.

The Moon Tonight

Its phase and face, drawn live for where you’re standing.

✦  Astronomy Picture of the Day  ✦

Cap Cloud over the Sierra Nevadas

November 26, 2013
© Guido Monta��s
One might say this was a bell weather day for the Sierra Nevada mountains. In January, just as the Sun was setting above the district of Albayz�n in Grenada, Spain, a huge cloud appeared as a bell capping the Veleta peak. Such a Cap cloud is formed by air forced upwards by a mountain peak, with the air then cooling, saturating with moisture, and finally having its molecular water condense into cloud droplets. Such a bell-shaped cloud structure is unusual as air typically moves horizontally, making most clouds nearly flat across at the bottom. Vertical waves can also give additional lenticular cloud layers, as also seen above. Given the fleeting extent of the great cloud coupled with momentarily excellent sunset coloring, one might considered this also a bellwether day for an accomplished photographer. Print or Peruse: Free APOD 2014 Calendar in PDF format

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✦  EarthSky  ·  Astronomy.com  ·  Phys.org  ✦
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