earthterminator_iss002_920The terminator, that is, the line between day and night, on the airless moons pictured here from time to time, is a firm line. No such sharp boundary marks the boundary between day and night in this picture of ocean and clouds on Earth. Instead, the shadow line is diffuse and shows the gradual transition to darkness as twilight falls. The Sun illuminates the scene from the right, and the cloud tops reflect gently reddened sunlight filtered through the troposphere, the lowest layer of the atmosphere. The upper atmosphere scatters blue sunlight and fades into the blackness of space.

This picture actually was taken in June, 2001, from the International Space Station orbiting at an altitude of 390 km.

Image Credit: NASA

Eclipses Seen From Orbit

SDOEarthEclipse-LunarTransit2013NASA’s Solar Dynamics Observatory (SDO) recently entered its semiannual eclipse season, a period of three weeks during which Earth blocks its view of the sun for a part of each day. Yesterday, SDO observed two transits. Earth blocked SDO’s view of the Sun from about 06:15 to 07:45 UTC, and from around 11:30 to 12:45 UTC, the Moon moved between the satellite and the Sun for a partial eclipse.

The edge of Earth’s shadow appears fuzzy. That’s because some light from the Sun comes through Earth’s atmosphere. The shadow line of the Earth appears almost straight because the Earth is much closer to SDO and appears to be larger than the Sun.

Because the moon has no atmosphere, its curved shape can be seen clearly, and the line of its shadow is crisp and clean. Any spacecraft observing the sun from Earth orbit has to deal with such eclipses, but SDO‘s orbit is designed to minimize their interference.

Image Credit: NASA

You’re On That Small Blue Dot

newrings_cassiniBack in 2006, the Cassini spacecraft orbiting Saturn drifted in giant planet’s shadow and looked back toward the eclipsed Sun. Saturn’s rings lit up so much that new rings were discovered, although they are hard to see in this image. Saturn’s E ring, the ring created by the newly discovered ice-fountains of the moon Enceladus and the outermost ring visible above, does show up in vivid detail. Far in the distance, at about 10 o’clock on the left, just above the bright main rings, is the almost ignorable pale blue dot of Earth. You may have to click on the image to embiggen it in order to see the Earth.

Image Credit: NASA

Earth From Mars

This picture of Earth from Mars was captured by the Mars Global Surveyor spacecraft orbiting Mars. It is possible to make out the Pacific Ocean, clouds, much of South America, and part of North America. Earth’s Moon is visible on the upper right, with the large crater Tycho brightening the lower part.

Image Credit: NASA/JPL

We’re On The Larger Dot

This picture of Earth (left) and the moon (right) was taken by NASA’s Juno spacecraft on 26 August, 2011, when the spacecraft was about 6 million miles (~9.7 million kilometers) away. It was taken by the spacecraft’s onboard camera, JunoCam. The spacecraft is en route to Jupiter, arriving in 2016.

Image credit: NASA/JPL-Caltech/SwRI

You Are Here

This image of the Earth, called Pale Blue Dot, is a part of a family portrait of the solar system taken by Voyager 1. The spacecraft took 60 frames for a mosaic of the solar system looking back from a distance of over 4 billion miles from Earth. From that distance Earth is a tiny point of light, a crescent only 0.12 pixel in size. At the time its picture was taken, Earth happen to lie right in the center of one of the scattered light rays resulting from taking the image near the sun. This enlarged image of the Earth was taken through three color filters—violet, blue and green—and recombined to produce the color image. The background noise in the image is an artifact resulting from the high magnification.

Image Credit: NASA/JPL