Approaching the Equinox

September 12, 2018

GMVS_August 31_2018

Image Acquired from NOAA Geostationary Satellite Server 
Summary Author: Jim Foster

Geostationary satellites revolve in the same direction that the Earth rotates (west to east). At their very high orbital altitudes (about 22,300 mi or 35,800 km) a complete orbit takes the same number of hours required for the Earth to rotate once on its axis -- approximately 24 hours. These satellites are designed to watch for atmospheric conditions that may lead to the development of severe weather (particularly hurricanes) and if storm systems form they're able to then monitor their movement. They're also ideal for keeping tabs on changes in the amount of daylight as one season changes to another.

The image above shows a view of the Earth, in visible light, directly over the Equator, as observed by Meteosat 9 on August 31, 2018 (0600Z). This satellite is positioned over the Prime Meridian (0 degrees longitude). At this time of year, the period of daylight and darkness in both the Northern and Southern Hemisphere's is nearly the same. Note that the Earth's terminator, separating day from night, is skewed a bit toward the Northern Hemisphere (the South Pole is still dark) since the image was acquired 3-weeks before the actual date of the Northern Hemisphere's autumnal equinox, September 21.