Tuesday, June 29, 2004

Look homeward, angel.

Tom has us looking at Saturn from the Cassini spacecraft as it approaches the ringed planet. How about a look back our way.

The Sun is far and away the brightest non-Saturnian object in the sky, although nearly a hundred times less bright than it appears from Earth and ten times smaller. It blazes in a star-sprinkled sky in the constellation Sagittarius, near the edge of the Milky Way.

Earth is visible about a finger-span of your outstretched arm from the Sun's disk, a bit brighter than the stars of Orion's belt. Earth is presently on the opposite side of the Sun from Saturn, so we're looking upon its almost fully illuminated face.

Venus glows several times brighter than the Earth, even closer to the Sun.

Mercury -- barely visible to the eye -- appears farther from the Sun than Earth or Venus, but that is because of the alignments of the planets in their orbits on this particular day.

Mars floats in the Milky Way, on the edge of naked-eye visibility. We are seeing mostly its dark side.

Jupiter is brightest of all, about as bright as the brightest stars, about three handspans away from the Sun.

If you were aboard Cassini, looking back you'd surely feel a pang of separation anxiety.