Common characteristics of IFOs (Identified Flying Objects), which are naturally occurring by day, include clouds (especially lenticular), flocks of birds, atmospheric phenomena such as "sun dogs" and "mock sun." Common characteristics of IFOs which are naturally occurring by night include stars, planets (especially Venus), meteors and atmospheric phenomena such at St. Elmo's fire and ball lightning.
Common characteristics of IFOs which are man-made and observed by day include unusual planes, balloons of different types, and helicopters. Man-made IFOs observed at night are usually airplane lights, satellites, spotlights, and advertising on strips trailing behind planes.
Common characteristics of UFOs (Unidentified Flying Objects) can be described in terms of their appearance, their behavior, and their unusual effects.
1. UFOs generally appear in four main shapes: the disc (or saucer), the enormous triangle, the cylinder, and the sphere. They often exhibit brilliant luminosity, illuminating the terrain beneath, and shooting out beams of light. These beams are sometimes truncated. There is often a pulsation of a full spectrum of colors. Frequently, they are surrounded by vapor, sometimes appearing in cloud-like lenticular forms. Often the objects are domed, have portholes, and have a metallic-looking, shiny, lightly-colored surface.
2. The behavior patterns of UFOs varies. Often there is a prolonged hovering, which is almost motionless, followed by an extreme acceleration which is frequently straight upwards. Another familiar flight pattern is an erratic, non-linear, non-smooth, zigzagging, darting motion. Sometimes the vehicles seem to flip end over end, or to stand upright in flight, or to fall like leaves. They are able to make very sudden right angle turns at enormous velocities. They exhibit super-sonic speed with no sonic boom. In fact, there is rarely any sound, sometimes just a high frequency, low volume humming sound.
3. UFOs have unusual effects upon their immediate surroundings. Animals may behave strangely, often panicking, cows' milk production ceases, etc. Electromagnetic effects cause electrical malfunction to occur - car engines stop running, as well as car radios, headlights, etc. - as soon as the UFO is in close proximity. Upon departure of the UFO, all systems often start up again on their own. Furthermore, there may be signs of radiation effects on humans, animal and plant life in the immediate area as well as feelings of cold or heat.
4. UFOs leave after-effects on the ground. Impressions are often left forming a geometric design. Soil and vegetation in the affected area is dehydrated and will not absorb water. Affected vegetation will not seminate, or regrow for a long time.