Michelangelo, who painted the ceiling of the Sistine Chapel, was born this day in 1475.Whereas his work is considered great art, some images that appear on ceilings are not considered as such. Do you have mysterious lines on your cathedral ceiling? Dark streaks that appear for no apparent reason? Dark stains that run along cathedral ceiling joists are called "ghosting." Ghosting is a phenomenon caused by temperature differences between the underside of the joist, which is cooler, and the open space between them, which is warmer because it is insulated. The result is a tiny bit of condensation on the drywall just below the joists that grabs dust and airborne particulates. From things such as candles, cigarettes and cooking -- over time -- it darkens, and lines begin to appear. The solution? Add more ceiling insulation (which isn't easy in cathedral-type ceilings), or improve warm-air circulation with a ceiling fan. Reducing dust and soot helps, too. For more tips, visit our Web site at Onthehouse.com.