MGS MOC Release No. MOC2-380, 3 June 2003
Mars Global Surveyor orbits the red planet 12 times each day. Half of each orbit is spent on the day side of Mars, which is where most Mars Orbiter Camera (MOC) images are obtained because sunlight is required to illuminate the surfaces being observed. However, on the night side of Mars, the wide angle cameras can see clouds and hazes above the sunward martian limb. The limb is the edge of the planet as it appears when viewed from an oblique perspective.
This blue wide angle camera image, obtained on the night side of Mars on May 15, 2003, shows clouds picking up the first sunlight before dawn near 55° north latitude. The scene is illuminated by sunlight from the right. The sun is actually on the other side of the planet, and has not yet risen over this region. The dark area on the left side of the picture is the martian surface at night. The dark band on the right side is outer space. The bright features just right of center are the clouds hanging above the martian limb over the planet's northern plains. North is toward the top and east is to the right; the spacecraft was moving southward when the image was acquired.