Winter Solstice Arrives in Northern Hemisphere

Image acquired December 22, 2011 NOAA's GOES-13 satellite captured this image of Earth on the first day of the winter solstice, December 22, 2011 at 11:45 UTC. The GOES-13 cloud images are overlaid on a true-color NASA/MODIS map by the NASA/NOAA GOES Project at NASA's Goddard Space Flight Center in Greenbelt, Md. <a href="http://goes.gsfc.nasa.gov/" rel="nofollow">Credit: NOAA/NASA GOES Project</a> <a href="http://www.nasa.gov/audience/formedia/features/MP_Photo_Guidelines.html" rel="nofollow">NASA image use policy.</a> <a href="http://www.nasa.gov/centers/goddard/home/index.html" rel="nofollow">NASA Goddard Space Flight Center</a> enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on <a href="http://twitter.com/NASA_GoddardPix" rel="nofollow">Twitter</a> Like us on <a href="http://www.facebook.com/pages/Greenbelt-MD/NASA-Goddard/395013845897?ref=tsd" rel="nofollow">Facebook</a> Find us on <a href="http://instagrid.me/nasagoddard/?vm=grid" rel="nofollow">Instagram</a>

The North

Reflected sunlight is the source of the illumination for visible wavelength images such as the one above. However, at longer infrared wavelengths, direct thermal emission from objects dominates over reflected sunlight. This enabled instruments that can detect infrared radiation to observe the pole even in the dark days of winter when Cassini first arrived at Saturn and Saturn's northern hemisphere was shrouded in shadow. Now, 13 years later, the north pole basks in full sunlight. Close to the northern summer solstice, sunlight illuminates the previously dark region, permitting Cassini scientists to study this area with the spacecraft's full suite of imagers. This view looks toward the northern hemisphere from about 34 degrees above Saturn's ringplane. The image was taken with the Cassini spacecraft wide-angle camera on April 25, 2017 using a spectral filter which preferentially admits wavelengths of near-infrared light centered at 752 nanometers. The view was acquired at a distance of approximately 274,000 miles (441,000 kilometers) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 111 degrees. Image scale is 16 miles (26 kilometers) per pixel. The Cassini spacecraft ended its mission on Sept. 15, 2017. https://photojournal.jpl.nasa.gov/catalog/PIA21351

Saturn, Approaching Northern Summer

Since NASA's Cassini spacecraft arrived at Saturn in mid-2004, the planet's appearance has changed greatly. The shifting angle of sunlight as the seasons march forward has illuminated the giant hexagon-shaped jet stream around the north polar region, and the subtle bluish hues seen earlier in the mission have continued to fade. Earlier views obtained in 2004 and 2009 (see PIA06077 and PIA11667) demonstrate how drastically the illumination has changed. This view shows Saturn's northern hemisphere in 2016, as that part of the planet nears its northern hemisphere summer solstice in May 2017. Saturn's year is nearly 30 Earth years long, and during its long time there, Cassini has observed winter and spring in the north, and summer and fall in the south. The spacecraft will complete its mission just after northern summer solstice, having observed long-term changes in the planet's winds, temperatures, clouds and chemistry. Cassini scanned across the planet and its rings on April 25, 2016, capturing three sets of red, green and blue images to cover this entire scene showing the planet and the main rings. The images were obtained using Cassini's wide-angle camera at a distance of approximately 1.9 million miles (3 million kilometers) from Saturn and at an elevation of about 30 degrees above the ring plane. The view looks toward the sunlit side of the rings from a sun-Saturn-spacecraft angle, or phase angle, of 55 degrees. Image scale on Saturn is about 111 miles (178 kilometers) per pixel. The exposures used to make this mosaic were obtained just prior to the beginning of a 44-hour movie sequence. http://photojournal.jpl.nasa.gov/catalog/PIA21046