This idea has been around for awhile—I think it first appeared here as a Clementine Candle. Typically it is halved and a star-shaped vent is cut into the lid like so:
However, D and I are partial to satsumas, having spent many winters in Japan where consuming a 200-yen bag of mikan over the course of an evening is its own special joy. I also found that the vent quickly blackened and didn't look that great, so here is my resulting modification.
First you have to know that the stem end is going to sit down, as it has the long pith that serves as a wick.
Score your satsuma about 1/3 way down and carefully peel that away. Then pull the fruit out, have a little snack and—here's the critical step—go to bed. In my experiments, I found that shells which were left to dry overnight burned brighter. So I recommend letting it sit for at least a few hours.
|a dried satsuma shell|
Now all you have to do is add about a tablespoon of olive oil (other oils might work, but olive oil is particularly clean burning) and light the wick. This tiny little lamp will burn through dinner, dessert, and even a glass of wine and a game of cards afterwards. As I write this, mine have been going for over three hours.
You can also dress it up. I added some fragrant oil from the kids' soapmaking days and for good measure, cut the orange into petal shapes. I think a few of these would make a pretty centerpiece, or could even line up as a kind of menorah.
Here's to finding some brightness in your dark nights. Happy Solstice.