How do you remove oval ring stain left on hardwood floor after picking up area rug?

As wood ages it oxidizes at the surface. We call it Patina when it happened on a fine violin or a piece of furniture, but when you have a ghost image on your floor its not so great.

The area under the rug didn't get the light & oxygen to make it age or oxidize the same as the uncovered area so you usually get a light ghost of the rug and a dark outline around it

.Other than sand & refinish, only time will heal this.

If you remember science class this will have about a 6 month "Half Life" half the shade difference will be gone in 6 months & then half of that in another & so on. But it will always be there if you look close enough.