MARS DAY, 10 a.m.-3 p.m. tomorrow, Steven F. Udvar-Hazy Center, 14390 Air and Space Museum Pkwy., Chantilly. Operate a Mars rover; participate in the Red Planet quiz show, hands-on demonstrations and art activities; see a meteorite; and view the latest images from and learn about Mars from the Museum geologists and researchers. Free. 202-357-2700.
ARTS IN THE ALLEY, 11 a.m.-5 p.m. Saturday, 21st Street, Purcellville (across from Nichols Hardware). Displays of work in fiber, sculpture, paintings, photography, glass and metal. All work available for sale direct from artists. Artwork by area youth. A panel of judges will present awards. Musical entertainment, face-painting and food available for purchase. Free. 703-727-5025 or www.loudounsbest.com/art
LOUDOUN SUMMER MUSIC FEST, Sunday. Gates open at 5 p.m., concert at 6 p.m., Belmont Country Club, 43880 Russell Branch Pkwy., Ashburn. $10, adults; free, ages 12 and younger. Music by Starship. Face-painting and other children's activities. No food, drink or coolers; food and drink will be available for purchase. Sponsored by AOL, the Loudoun Foundation and Belmont Country Club to benefit local charities. 703-726-4343 or www.summermusicfest.net.