Opposition is when a planet appears on the opposite side of the sky from the Sun. As Saturn takes 29 years to make a single circuit of the Sun, this happens once a year (it actually takes a year and a few extra days because Saturn moves against the background sky a bit — the last opposition was on March 22, 2010).
But this time opposition is a bit different. Saturn happens to be one of the only planets visible in the sky for most of the night. Mercury is lost in the Sun's glare until late in the month when it will be visible before sunrise. Venus rises at about 5:23 a.m. (Eastern) on April 1, and will stay visible in the predawn sky for the whole month. Mars, like Mercury, is too close to the sun in the sky to see, as is Jupiter.