How to Correct Event Times, Using the A-B Factor
Updated as of 10 Jun 2013

After Selecting the closest major city from the selections, use the A and B column to correct for your local time.

Where #Lg = the base longitude, and #Lt = the base latitude,
and where Lg is your local station longitude and Lt is your local station latitude,

And where #Lg, Lg, #Lt, and Lt are in decimal degrees, the corrected time (in minutes) is derived as such:

Base Station Time + (A * (Lg-#Lg)) + (B * (Lt-#Lt)) = Local Station Time

You need also to pay attention to the value sign of the number. The longitudes and latitudes must be expressed with the correct sign. Longitudes are measured positive to the East, and Latitudes are measured positive to the North. Note that longitudes in North America have a negative value. As a simple rule of thumb:

• (Lg - #Lg) will be a positive number if you are East of the base station
• (Lg - #Lg) will be a negative number if you are West of the base station
• (Lt - #Lt) will be a positive number if you are North of the base station
• (Lt - #Lt) will be a negative number if you are South of the base station

Example Problem:

On 22 Jun 2013 at 3h 10m 54s, SAO18479 will be occulted by the moon for Bonner Springs KS, located at: W -94d 53m 35.5s, N 39d 3m 28.6s

The given A/B factor by the Occult Software shows A = +1.9, B = +1.2

Find the predicted time for a site located in Blue Springs MO, located at: W -94d 20m 42.4s, N 39d 1m 40.2s

Convert the Base Station coordinates to decimal degrees: #Lg = -94.8932 and #Lt = 39.0579

Convert the Local Site Location coordinates to decimal degrees: Lg = -94.3451 and Lt = 39.0278

Solve for the unknowns in (A * (Lg-#Lg)) + (B * (Lt-#Lt))

A * (Lg - #Lg) = 1.9 * (-94.3451) - (-94.8932) = 1.0412 [Lg-#Lg = Positive which shows local station longitude is EAST of Base]

B * (Lt - #Lt) = 1.2 * (39.0278) - (39.0579) = -.03613 [Lt -#Lt = Negative which shows local station latitude is SOUTH of Base]