Hi

A Y wing is facing away from the imperial assault carrier and slightly behind it. The shortest distance is range 1 to the back of the imperial assault carrier. But the front is range 2. Cant the y wing shoot at the front of the imperial assault carrier?

Depends. You can shoot the fore section as long as your firing arc does not cross the blue center line. Here is the relevant text:

Targeting a Huge Ship

To target a huge ship, choose a section (either fore or aft) of a huge ship that the attacking ship can target normally. Then, measure a line from the exact center of the attacking ship’s base to the exact center of the base for the chosen section of the huge ship. If this line is not obstructed by the blue center line on the huge ship’s ship token, the attacker can declare the chosen section as his target.

The range of the attack is determined by the line measured from the closest point of the attacking ship to the closest point of the chosen huge ship’s section that is inside the attacking ship’s firing arc. If using an attack that ignores firing arcs, measure this line without regard to firing arc.

If the attacker determines that he cannot target the chosen section, he may choose another target.

ahhhh that exact hint I was looking for. thanks

You can shoot the fore section as long as your firing arc does not cross the blue center line.

No, you can shoot the fore section as long as it's within your firing arc, and a line drawn from the center of your ship, to the center of the section you want to target does not cross the blue line.

It's in the text you quoted.

Correct. I was typing fast early this morning...

Let's say in your position your arc does not cross the blue line and you have a clear shot at the raider

You are range one of the back and range two of the front, you can shoot the front but not the back