- The Aleutian Islands seem to be dividing two large weather systems in this Moderate Resolution Imaging Spectroradiometer (MODIS) image, collected on January 21, 2006, by NASA’s Terra satellite. The clouds define the lines of high and low air pressure as well as any weather map. In the top of the image, the clouds circle clockwise around a high-pressure system in an anticyclone, while a cyclone in the bottom section of the image swirls counter-clockwise around a low-pressure system. The center of the anticyclone contains air that is under high pressure, so air entering the system is pushed down and out, away from the center. The spin of the Earth sends this air into a clock-wise circle. In this image, only the bottom half of the anticyclone, where the air flows over open water and clouds form, is clearly visible. A cyclone, by contrast, rotates around the center of a low-pressure system. In this case, air rises as it rushes into the area of low pressure. The opposite direction of this movement (up and in instead of down and out) means that the air is pulled into a counter-clockwise rotation around the center. Anticyclones usually bring fair weather, while cyclones carry rain and strong winds. Both cyclones and anticyclones are common in the Arctic during the winter. Their formation is driven by temperature differences between the frigid, frozen land and the warmer ocean. The cyclone seen here is a semi-permanent feature called the Aleutian Low.
- But immediately upon this I observed that, whilst I thus wished to think that all was false, it was absolutely necessary that I, who thus thought, should be somewhat; and as I observed that this truth, I think, hence I am, was so certain and of such evidence, that no ground of doubt, however extravagant, could be alleged by the Sceptics capable of shaking it, I concluded that I might, without scruple, accept it as the first principle of the Philosophy of which I was in search.
