looked like glowing orangey-red balloon shape

it hovered over a house then moved across the road in a westward direction changing its speed rapidly. It was either a small object 100feet up or a larger object higher.

I was in a car with my dad and brother going home from an other brothers house, and was going to take the Cardiff road to Penarth. My dad saw it first and was very puzzled, he followed it down the Llantrisant road until it disappeared behind a bunch of trees. I thought it was a flame of some sort around a spaceship, I also thought it was a star burning but I then realised it couldn't have been as stars don't move. I couldn't find my camera so there is no picture. My brother(14)is unbelieving and said it was a hot-air balloon. My dad(an engineer, and MBA, who is interested in astronomy, like me)thought the only thing it could look like was a hot-air balloon, but also said the sky was too dark,it was too windy, and it moved too quickly to be one