  The "cosmic triangle" is introduced as a way of representing the past,
present, and future status of the universe. Our current location within the
cosmic triangle is determined by the answers to three questions:
  How much matter is in the universe?
  Is the expansion rate slowing down or speeding up?
  And, is the universe flat? A review of recent observations suggests a
universe that is lightweight (matter density about one-third the critical
value), is accelerating, and is flat. The acceleration implies the existence of
cosmic dark energy that overcomes the gravitational self-attraction of matter
and causes the expansion to speed up.
