Is atheism a belief?

[T0 Th3 M4X]

All adult atheists, who have heard and rejected religious claims, have one belief in common. 

They believe that the claims of religion are unpersuasive.

My word but you are wrong a lot.  Atheism is a belief in the same way that not collecting stamps is a hobby or bald is a hair colour.

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For me, as an atheist, I find it rational to believe the Sun exists based upon the evidence we have for it's existence.

It's actually irrational to believe the sun exists.  We have more than sufficient evidence to accept the existence of the sun, just like I have more than sufficient evidence to accept the existence of the chair I'm sitting in or the keyboard I'm typing this post with.

Belief only comes into play when there is insufficient evidence for acceptance, or with religion, an utter lack of evidence at all.

If someone says:

"I believe the earth's orientation is flat "

and I say:

"I believe the earth has a spherical orientation."

Is my statement to them irrational?  Where did you get the idea that "belief" is irrational?  Do you have an objective source for this?