Aurora Over Clouds
2.04.2001

Aurorae usually occur high above the clouds. The auroral glow is created when fast-moving particles ejected from the Sun impact air molecules high in the Earth's atmosphere. An oxygen molecule, for example, will glow in a green light when reacquiring an electron lost during a collision with a solar particle.

Mysterious White Rock Fingers on Mars
7.04.2008

What caused this unusual white rock formation on Mars? Intrigued by the possibility that they could be salt deposits left over as an ancient lakebed dried-up, detailed studies of these fingers now indicate that this is not correct.

Nacreous Clouds over Sweden
10.01.2020

Vivid and lustrous, wafting iridescent waves of color filled this mountain and skyscape near Tanndalen, Sweden on January 3. Known as nacreous clouds or mother-of-pearl clouds, they are rare. This northern winter season they have been making unforgettable appearances at high latitudes, though.

Aurora in Red and Yellow
10.04.2000

The past week brought some spectacular aurora to northern skies. These aurorae were caused by a large interplanetary shock wave that exploded from the Sun on April 4. When the shock wave reached the Earth on April 6, the resulting aurora could be seen in clear skies as far south as North Carolina.

Noctilucent Clouds, Reflections, and Silhouettes
26.06.2019

Sometimes it's night on the ground but day in the air. As the Earth rotates to eclipse the Sun, sunset rises up from the ground. Therefore, at sunset on the ground, sunlight still shines on clouds above.

Venus and the Triply Ultraviolet Sun
20.08.2013

An unusual type of solar eclipse occurred last year. Usually it is the Earth's Moon that eclipses the Sun. Last June, most unusually, the planet Venus took a turn. Like a solar eclipse by the Moon, the phase of Venus became a continually thinner crescent as Venus became increasingly better aligned with the Sun.

Venus and the Triply Ultraviolet Sun
4.02.2018

An unusual type of solar eclipse occurred in 2012. Usually it is the Earth's Moon that eclipses the Sun. That year, most unusually, the planet Venus took a turn. Like a solar eclipse by the Moon, the phase of Venus became a continually thinner crescent as Venus became increasingly better aligned with the Sun.

Noctilucent Clouds
26.07.1999

Sometimes it's night on the ground but day in the air. As the Earth rotates to eclipse the Sun, sunset rises up from the ground. Therefore, at sunset on the ground, sunlight still shines on clouds above.

Is Mystery Object an Orphan Afterglow
12.11.2001

What is that unusual object? Astronomers can identify most objects that are imaged on the sky, but not all. Pictured above is one that currently defies classification. Attributes of the object include that it has unusual colors, appears to be fading as months go by, and appears to be associated with a distant galaxy.

Highlights of the North Winter Sky
5.12.2018

What can you see in the night sky this season? The featured graphic gives a few highlights for Earth's northern hemisphere. Viewed as a clock face centered at the bottom, early (northern) winter sky events fan out toward the left, while late winter events are projected toward the right.