Does Astral Heron so itself when played so the next card will have the discount

No, Astral Heron does not discount itself.

According to its ability text, the discount triggers "When you play your first card each turn." Since you must play Astral Heron (or another card) to trigger the ability, the discount applies to the next card you play after the Heron has already entered play.

Here is the breakdown of why:

1. Triggered Ability: The ability is a "When you play..." triggered ability. These triggers go on the chain after the card that triggered them (in this case, the Astral Heron itself) has already entered play.
2. Timing: Because the discount is generated by the Heron’s triggered ability resolving, it only exists for cards played subsequent to the resolution of that ability.
3. Cost Determination: When you play the Astral Heron, its own cost must be paid before the card enters play and its ability can be placed on the chain. Therefore, it is impossible for its own discount to apply to its own cost.

In summary: You must pay the full cost to play the Astral Heron. Once it is on the battlefield, its "When you play your first card..." ability will trigger, creating a delayed discount that will apply to the second card you play that turn.