Venus Monitor Camera image taken in the ultraviolet (0.365 micrometers) from a distance of about 19,000 miles (30,000 kilometers).
It shows numerous high-contrast features caused by an unknown chemical in the clouds that absorbs ultraviolet light, creating the bright and dark zones.
With data from Venus Express, scientists have learned that the equatorial areas on Venus that appear dark in ultraviolet light are regions of relatively high temperature where intense convection brings up dark material from below. In contrast, the bright regions at mid-latitudes are areas where the temperature in the atmosphere decreases with depth. The temperature reaches a minimum at the cloud tops, suppressing vertical mixing. This annulus of cold air, nicknamed the "cold collar," appears as a bright band in the ultraviolet images.