Most likely a basic question to most, been awhile since ive done any of this. If i remember right the formula states, F = G*M_1*M_2/d^2 where d = distance between M_1 and M_2 Im creating a planetary simulator for fun, i get the initial position of the earth using the 7 variable Astrological Guides technique. iniPos I then get a position + 1 day in the future call it pos2; Velocity = pos2-iniPos; Im using the grav-constant 6.67E-20 km^3/kg*s^2 1)So grav_constant*M_1*M_2 = grav_const*5.9742E24*1.988435E35 = 7.923498687E35 2)The distance between the the two is approx 150 000 000, according to the formula then d^2 = 2.25E16 Force = grav_constant*M_1*M_2/d^2 = 3.52155E19 km*Kg/s^2 Huge number! Forward Euler update shows us that the 'unit_vector' pointing towards the sun multiplied by the force should give us our update method. updateVelVector = oldVelVector + unit_vector*force*dt Where dt = change in time However this doesnt work worth a damn, Somewhere ive made a mistake and i just cant see it, Please help! PS i tried reducing the problem space to some number which i thought would be easier to use. I decided to decrease the distance to 1 km, basically this turns the problem into earth_mass/1.125E16 and sun_mass/1.125E16. This is wrong too, im very stuck!