it can't. acceleration is a change in velocity.
-- "declination zero" means the object is in the sky at some point directly over the earth's equator.
-- if it's the sun and it appears to be over the equator, then that tells us that the earth's axis is not tilted toward or away from it.
-- that in turn tells us that the earth is at one of the two equinoxes in its orbit, either the spring one or the autumn one. (d)
-- (the first days of summer and winter coincide with solstices, not equinoxes.)