September 20, 2010 - Delicate Dance of Shadows

Delicate Dance of Shadows Every six months the Earth’s axis of rotation is neither pointing toward the Sun nor away from it. At these times of equinox, or equal night, the Sun appears directly overhead at the equator at local noon, and days and nights there are exactly twelve hours long. Because Saturn takes much longer to orbit the Sun, an equinox there occurs about every fifteen years, but when it does, it sets the stage for a memorable play of light and dark as the shadows cast by Saturn’s moon fall directly on the planet’s rings. In April 2009, four months before Saturn’s equinox, the Cassini spacecraft captured this rare image. The shadow of its moon Tethys falls across the A ring and Cassini Division in this view, which looks toward the unilluminated side of the rings from about 50° above the ringplane.

Image credit: NASA / JPL / Space Science Institute

Weekly Calendar

September 20-26, 2010

Holidays - Sky Events - Space History

Moon phase Monday 20

Neptune 5° south of Moon

1945: Wernher von Braun arrives in United States
1966: Surveyor 2 launched
1970: Luna 16 lands on Moon
1979: HEAO-3 launched
1988: Israel launches its first satellite

Moon phase Tuesday 21

Moon at apogee
Jupiter and Uranus at opposition

1866: H. G. Wells born
: Gustav Holst born
1974: Mariner 10 flies by Mercury for second time
2003: Galileo mission ends

Moon phase Wednesday 22

Fall Equinox 11:09 PM
Jupiter 0.9° south of Uranus

1990: Pioneer 10 reaches 50 AU from Sun
2006: Hinode spacecraft launched

Moon phase Thursday 23

Full Moon 5:17 AM ET
Jupiter 7° south of Moon
Venus greatest illuminated extent

1783: Caroline Herschel discovers NGC 253
1846: J. G. Galle discovers Neptune
1962: “The Jetsons” premieres
1977: Third glide test of space shuttle Enterprise

Moon phase Friday 24

1930: John Young born
1962: MOOSE astronaut rescue system proposed
1970: Luna 16 returns lunar soil samples
1999: IKONOS-1 launched

Moon phase Saturday 25

1973: 59-day Skylab 3 mission ends
1992: Mars Observer launched
1997: STS-86 Atlantis launched
2008: Shenzhou 7 launched

Moon phase Sunday 26

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