ASTRO is convention used over a 1N opening to show 2-suited hands:
2 shows Hearts and a minor
2 shows Spades and another suit
Partner ("advancer") bids the major with 4+ or with 3 to an honor; otherwise, he bids the cheapest suit.
With an invitational hand, advancer jumps in the major if he has a fit; otherwise, he bids 2N.
Over intervention, advancer doubles to show support for the major and invitational strength. With a weak hand, advancer bids the major with support.