Explanation: When does a nebula look like a comet? In this crowded starfield covering over two degrees within the high-flying constellation of the Swan (Cygnus), the eye is drawn to the Cocoon Nebula. A compact star forming region, the cosmic Cocoon punctuates a nebula bright in emission and reflection on the lower right, with a long trail of interstellar dust clouds to the left, making the entire complex appear a bit like a comet. Cataloged as IC 5146, the central bright head of the nebula spans about 10 light years, while the dark dusty tail spans nearly 100 light years. Both are located about 2,500 light years away. A bright star near the colorful nebula’s center likely supplies power and helps clear out a cavity. The long dusty filaments of the tail, although dark in this visible light image, hide stars in the process of formation. The featured image was captured in July from Death Valley, California, USA.

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Tomorrow’s picture: triple eclipse

Explanation: If you went outside at the same time every day and took a picture that included the Sun, how would the Sun’s position change? A visual answer to that question is an analemma, a composite image taken from the same spot at the same time over the course of a year. The featured analemma was composed from images taken every few days at noon near the village of Callanish in the Outer Hebrides in Scotland, UK. In the foreground are the Callanish Stones, a stone circle built around 2700 BC during humanity’s Bronze Age. It is not known if the placement of the Callanish Stones has or had astronomical significance. The ultimate causes for the figure-8 shape of this and all analemmas are the tilt of the Earth axis and the ellipticity of the Earth’s orbit around the Sun. At the solstices, the Sun will appear at the top or bottom of an analemma. The featured image was taken near the December solstice and so the Sun appears near the bottom. Equinoxes, however, correspond to analemma middle points — not the intersection point. In two days there will be an equinox (“equal night”), when day and night are equal over all of planet Earth. Many cultures celebrate a change of season at an equinox.

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Tomorrow’s picture: open space

Explanation: Also known as the false dawn, a luminous band of zodiacal light is captured in this dark night skyscape. The serene view was recorded just before the beginning of astronomical twilight during September’s star party at the remote Hanle Dark Sky Reserve, Ladakh, India, planet Earth. At about 4,500 meters altitude, the dark sky reserve presents a haven for hardy stargazing and astrophotography enthusiasts. While meteors streak through the night, bright planet Jupiter appears immersed in the faint zodiacal glow near the eastern horizon. Follow the zodiacal band toward the zenith to find open star cluster M44 and a yellowish tinged planet Mars near the center of the frame. In fact, serendipitous detections of interplanetary dust by NASA’s Juno spacecraft suggest Mars itself is the source of dust that back scatters sunlight and creates zodiacal light in planet Earth’s night.

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Tomorrow’s picture: only sunny days