I've had one of these experiences once.
It was around 2 in the morning and my sister and I picked up a movie from the local red box. (My family is a bunch of night owls.)
Once I pulled into my street I noticed a green orb hovering above my car through the sunroof. The thing was moving with the car. Never changing altitude, just hovering.
I didn't think much of it and kept driving. I parked my little blue Kia on the street in front of my house. (Where I normally park). A pulled myself out of the car with the movie in hand. Out of curiosity I looked up one more time. The green orb hovered about 10ft above my car and was roughly the size of a bowling ball. No noise came from it, no odd smell, no electrical charge, just a sphere of green light.
As I stared I remember asking my sister " are you seeing this?" Her reply was an instant yes.
This is when it dawned on me what I might actually be seeing. In those seconds of realization it rose higher, stopped for a split second, and zoomed toward the small woods across the field. This sudden burst of speed wasn't like it disappeared, or that it became invisible once moving. No, this was graceful. It moved threw the air like a hot knife would glide through butter. It was as if the wind had no resistant to it as it moved. My immediate reaction was to chase the damn thing. I had to know what it was! I had to see this thing again.
I sprinted to the end of the road, stopping at the 'ROAD ENDS' sign and watched as it flew out of my field of vision.
My sister called out, telling me to come back.
"It's just past the tree line." I said, pointing.
"Then you can explain why you got muddy and sick". She said, or something similar to that. I agreed with great hesitation and began making my way back to the house.
Before I walked in I turned back to the tree line once more. Just to see if I would get another glimpse. In the distance, just past the tree line, there was a faint glow of green. I sighed heavily and went inside. Figuring I would never know what I truly saw.