The object was a dim point of light that grew to a brightness of twice what Venus would be and then disappeared & lasted ~ 15 seconds.I went outside to enjoy the night sky. It's 70 F degrees, clear skies with a few thin clouds. To the western sky is a very bright star low in the horizon. It's about 15 degrees or so. Worland is located approximately 44 degrees North Latitude and 108 degrees West Longitude. I'm 5 miles north on Wyo. Hwy. 433: West River Road. The bright star is due west. About 1/2 degree above and perhaps 3 degrees south of this star, I saw a small point of light moving from South to North. I assumed it was a satellite until it grew in brightness. I thought it might be a plane except there were no flashing lights and only the one point of light. It grew in brightness to twice that of the star which is about as bright as Venus would be. I thought it might be a plane turning towards me however it continued in a straight line to the north. At about the 2/3 point of it's arch which covered about the span of one hand at arms length, it reached its maximum brightness and then faded back to a dim point of light before disapearing. The event lasted about 15 seconds. As for my background, I'm retired Air Force and flew in B-52G's. I'm also a private pilot (licensed in the early '70's). This was not a plane. It was also not a meteor. The duration and relative slow speed of the sighting was without any "tail" of any kind. It was simply a dim spot of light that suddenly grew in intensity and then deminished. If you have questions, please contact me.