Is it a bird? Is it a plane?

As I'm sure most of you will be aware, there are phenomena both natural and man-made that at first are considered as UFOs but which, on closer examination, are easily explained or identified.

Aside from airships, party balloons, birds, Chinese lanterns, helicopters, planes, and shooting stars there are other less obvious examples. I have listed some of these below with a brief explanation and accompanying imagery where possible.

Flares

As used in air displays and these being sighted in a UFO context is not uncommon. This was in fact the basis of the official explanation for the well-documented 'Phoenix Lights' incident. Many witnesses to the event have subsequently pointed out that this explanation was flawed.

Laser displays 

As used in concerts and other external events. Having seen some of these myself it's easy to see how these could be picked up as UFO sightings, especially when viewed from a distance and where the sharpness and spread of the beams may vary depending on prevailing atmospheric conditions

Lenticular clouds

Though static these can sometimes form weirdly familiar shapes such as the one in this picture. Caused when stable moist air flows over a region of high ground, a series of large-scale standing waves may form on the downwind side. If the temperature at the crest of such a wave drops to the dew point, moisture in the air may condense to form these 'lens-shaped' clouds.

 
Mini-Camera Drones

Effectively a small remote-controlled 'copter with a mounted camera. I recall seeing a recent BBC article which says that the police in England will be rolling out the use of these in the coming years - so expect more supposed UFO sightings connected to these.



Rockets (and other space junk)

The explanation still being given for this weird spiral display over Norway in 2009 is that of the exhaust trail of a failing rocket. Pieces of man-made space junk, including parts of rockets and satellites with a decaying orbit that eventually fall to earth, are sometimes the source of UFO sightings.

Sun dogs

A rare weather effect that can make it appear as if there is more than one sun in the sky. This is caused by ice crystals acting as prisms, bending or refracting light passing through them.  Random patterns of these crystals can form a complete ring or 'halo' around the sun. However, where such crystals sink through the air they become vertically aligned, so sunlight is refracted horizontally forming 'sun-dogs'.



The star Sirius

Also known as the 'dog star' is the brightest star in the night sky, often to be seen very shortly after sunset and - although following a very slow path through the night sky - it has sometimes been reported as a UFO.

The planet Venus

Frequently used as an explanation for UFO sightings by sceptics down the years, it still prompts sighting reports. Only last month people were reporting sightings of Venus accompanied by Jupiter - viewed as a smaller companion 'star' in relation to Venus - in the night sky. To those not familiar with the recent position of these two planets in the night sky this must have seemed an unusual sight.

Obviously the above examples are not exhaustive. Where I come across others I will post these too.