Back in the 1970s, before the advent of the 'black budget,' the US Air Force budget included enormous expenditures for a mysterious aircraft known among air aficionados as Aurora, but being developed under the code name Bright Buzzard. For years, the USAF has denied the existence of this plane, but this photograph, taken by a plane spotter in Amarillo, Texas, may be the first actual evidence of its existence. For more, click on the source link.
At the same time that this triangle was observed over Amarillo, another, far more mysterious one flew low over witnesses in Virginia. For that story, click here.