Glowing craft in the sky changed shape and elevation, defying the laws of physics

The craft was seen by me and my girlfriend as we were driving down the highway.  This occurred at around 6:00pm, right as the last bits of light had left the sky.  It was seen in a farm field bordering a forest, around 40-50 feet in the air, right near the tree tops.  There was no other sources of light or buildings in the area.
 The craft was sitting still when we first saw it, and the entire craft was glowing a pale yellow.  It was probably the size of a small sedan.  It was originally in the shape of a disk, however, the disk was vertical, so the craft looked like the letter “I” when we first saw it.  It quickly flew to a horizontal position and then looked like a minus sign.  From there, it flew up about 10 feet and turned into a sphere. The craft seemed to defy the laws of gravity, and it quickly changed shape and elevation for about 1 minute until it was out of view.