How do I find the instantaneous acceleration of the earth orbiting the sun? Everything I am trying is incorrect.

Question

I am using 1 second as my time and get 1.99E-7 rads/second.

First I tried:

acceleration = theta x t / radius

Where: theta = 1.99E-7 rads
radius = 6.371E6

Then I tried s = r x theta

Where r = 6.371E6 and theta = 1.99E-7