Astro is a contract bridge

Contract bridge

Contract bridge, usually known simply as bridge, is a trick-taking card game using a standard deck of 52 playing cards played by four players in two competing partnerships with partners sitting opposite each other around a small table...

 bidding convention used to intervene over an opponent's 1NT opening. Requiring an unbalanced hand with at least nine cards in two suits, at least one of which is a major, Astro is initiated by a 2-level overcall in a minor suit:

• 2 shows at least 5-4 or 4-5 length in hearts and a minor suit, and
• 2 shows at least 5-4 or 4-5 length in spades and another suit.

The name is derived from the initials of the surnames of its inventors - Paul Allinger, Roger Stern and Lawrence Rosler.

Subsequent bidding

For purposes of subsequent bidding, the major suit indicated by the Astro Intervener is termed the “anchor major”; the cheapest unbid suit is called the "neutral" suit.
Depending upon action taken by the responder to the 1NT opener, Advancer may:

• Pass when weak and holding six cards in the minor bid by the Intervener, or
• Raise the anchor major: (a) to the 2 level with at least 3-card support, preferably with an honour, and no game intentions, or (b) raise to the 3 level with at least 4-card support and inviting game, cognizant of vulnerability and the point range of the 1NT opening, or (c) raise to the 4 level with at least 4-card support for game-try, or
• Bid an artificial and forcing 2NT to show some support in the anchor suit, game interest but no potential to bid further, or
• Bid a new suit take-out or new suit jump, to show a 6-card or longer suit, or
• Make a negative bid of 2 in the neutral suit to indicate having no other options, usually less than 3 cards headed by an honour in the anchor suit and at least a doubleton in the neutral suit.

Intervener rebids include:

• Pass after a neutral response with five cards in the neutral suit, or
• a bid of the anchor major to show 5 cards, or
• a bid of the second suit at the 3-level to show 6 cards and good playing strength.

Defense against Astro

Responder to the 1NT opener may:

• Double with holdings in the anchor suit and in the minor overcalled, or
• Cuebid the anchor suit when the hand is unsuited to defense, or
• Pass, waiting, or
• Bid a natural 2NT, invitational to game.

Variations

In the following variations of Astro, the overcalls indicate more specific information about suit combinations:

Modified Astro:

• 2 shows a long heart suit with or without a long minor
• 2 shows spades and a minor suit
• 2 shows hearts and spades

Pinpoint Astro:

• 2 shows hearts and clubs
• 2 shows hearts and diamonds
• 2 shows hearts and spades
• 2 shows spades and a minor suit

Roth-Stone Astro:

• 2 shows clubs and spades
• 2 shows diamonds and spades
• 3 shows clubs and hearts
• 3 shows diamonds and hearst
• Double shows hearts and spades against a strong 1NT opening; against a weak 1NT, it shows nothing about the majors but shows at least 15 high card points.

Several other bidding conventions use a variety of overcall schemes to compete against a 1NT opening; these include: Brozel

Brozel

Brozel is a method for intervening against an opposing 1NT opening bid. It features the following calls:*Double – shows any single suit; advancer bids 2, after which intervenor corrects to his actual suit...

, Landy

Landy

Landy is the first bridge conventional defense against over opponent's 1NT opening and one of the first conventions ever introduced. It was invented by Alvin Landy. Over 1NT, the overcall of 2 shows both major suits, while all other bids are natural...

, Aspro, Asptro, Ripstra, Cappelletti

Cappelletti

Cappelletti is a contract bridge bidding convention used to intervene over opponent's 1NT opening. Its invention is usually attributed to Michael Cappelletti and his longtime partner Edwin Lewis, but origin of the concept is also claimed by Fred Hamilton, John Pottage and Gerald Helms.Cappelletti...

 and DONT

DONT

DONT is a conventional overcall against an opposing 1NT opening bid. DONT, an acronym for Disturb Opponents' Notrump, was designed by Marty A. Bergen, and is therefore also referred to as 'Bergen over Notrump'. Although the method is often criticized for being too nebulous, it remains fairly popular...

.