# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

**Re: Moon Venus Lunar - Interpretation of results**

**From:**Paul Hirose

**Date:**2020 Feb 3, 11:00 -0800

To determine lunar distance rate, my program begins with the space velocity vectors of the bodies and resolves them into components (radians per day) that are perpendicular to the line of sight and in the plane of the observer and both bodies. I could show a worked example but the math would be tedious and probably not helpful. To practical accuracy you can use the obvious algorithm: get coordinates of the Moon and Venus one minute apart, then calculate the separation angle rates. For example, here are topocentric apparent right ascension and declination (degrees, with respect to the true equator and equinox) for 42.97 N 70.95 W from the JPL Horizons online calculator: Moon 2020-Jan-29 22:10:00 6.47496 -3.38550 2020-Jan-29 22:11:00 6.47991 -3.38218 Venus 2020-Jan-29 22:10:00 350.68358 -5.08514 2020-Jan-29 22:11:00 350.68433 -5.08478 At 22:10 the angular separation is 15.83885°. One minute later it's 15.84337. Difference is .00452°, or .271′ (increasing with time). In one minute the Moon moves .00595° and Venus .00083. Total angular velocity is therefore .00678° per minute. But the bodies are not moving directly toward or away from each other, so their separation changes just .00452° per minute, or 67% of the total angular velocity. Any coordinate system will work for the angular separation rate calculation. However, to calculate percentage utilization of the total angular velocity you can't use a coordinate system which rotates with the Earth, such as az/alt. On my first attempt I made that mistake. That's why I have a program to do this stuff.