Can someone explain the 'cusp' to me please?

[Ball-Bhreac Ròn]

Could someone please explain the 'cusp'? I mean, I know what it is (being born in two signs) but the way I see it, at the precise moment someone's being born, isn't the sun in either one sign or the other? And I know it varies from year to year, but wouldn't it make sense to stick with that one sign, if you wanted an accurate reading?
Just wondering, sorry if it's an ignorant question :lol:

[Xander67]

well, the tuem cusped is used to describe a person who was born either a few days befor or after the date of the next sign, true the precise moment helps, but astrology can go way deep, and some times, a person can actually be influenced by a nieghboring sign if his or her birthdate is close to it

[Ball-Bhreac Ròn]

aahh, ok :) Thank you!