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# Astronomy Calculations: Excel sheets

My Excel sheet collection.

I don't take any responsible for this, they can have errors in it! Use them at your own risk! ## Orbit Calculator:

Gravity, Kepler and Newton are exiting physics. Here I have made an orbit calculator. Simplified to only circular orbits.

There are two forces that push and pull radially on a planet in an orbit around the Sun. To get them in equilibrium the forces have to be equal strong. We don't want the planet crash into the Sun or escape and fly away.

Force Equations:
In this case Solar system, simple case when Suns mass is much bigger then any planet mass:

Gravity force between two masses Inward force +   Comments
F1 = G*M1*m2/r2 G=gravity constant M1=mass (Sun) m2=mass (planet)

Centripetal force from rotation Outward force -

Set F1+F2 = 0 and solve for v
v = square rot (G*M1/r) v=orbital speed r=distance between objects

In binary star systems it's common that the masses of the stars are note very different. We can't simplified the equations as much as we did above. The center of mass is somewhere between the stars. Both stars orbit around this point.

Orbital period, tangential speed and common mass center (barycenter)
We need more precise equations:

T = square rot (4*pi*a3/G(m1+m2) ) T=orbital period m1, m2 mass of the stars a=semi major axis

Tangential speed
V1 = 2*pi*a1
V2 = 2*pi*a2
Vx=tangential speed of star x ax=semi major axis star x

Center of mass
a1 = m1*a / (m1 + m2)
a2 = m2*a / (m1 + m2)
ax=distance mass center star x

Put the equations in an Excel sheet like the one below: Play around with the figures and help Newton, put in your own planets and objects. You only need the distance between the object to the Sun or the Earth, write it in the red fields.

The escape velocity from Earth is 11.2 km/sec, compare that with ISS station orbital speed above.

Both objects rotate around a common gravity center, but if one of the objects has much more mass it's like that one is still and the other rotate around the heavy one.