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Skills of Backyard Astronomy:

2) Distance Relationships:  If we know how an objects is from us we can use its angular size to determine how big it is using the Small Angle Formula.

D = A x d  / 206265

where

D = Physical Diameter
A = Angular Diameter (in arcseconds)
d = Object Distance
206265 = 360° x 3600"/ 1° / 2p

So what do we use for the Distance?

In science it is very important use consistent units so that everyone knows what you are talking about.

For instance 1 mi = 1.609 km

In this course we will use metric measurements, so the answer to the distance question is kilometers (or meters etc.), but it will work for any units so long as they are consistently used!  Unit inconsistency is the reason that the Mars Climate Orbiter failed.

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