- What is the other name of the constellation Sygnus?

The Southern Cross.

- What is Deneb?

It is a super-giant star with the luminousity of 160,000 suns.

- What can you see halfway between the stars Altair and Alberio?

The constellation "Coathanger".

- Which planet dominates the September sky?

Jupiter.

- When is the Autumnal Equinox this year? Where does the sun rise on this day?

On 22nd September at  05:22. The sun rises exactly on the East on this day.