The correct answer is $\boxed{\text{B}}$.
The circumference of the Earth is about 40,075 kilometers. This means that 1 degree of latitude is equal to about 111.3 kilometers. The Moon’s circumference is about 1,737 kilometers. This means that 1 degree of latitude on the Moon is equal to about 30 kilometers.
Therefore, two astronomical positions on the Moon that differ by 1 degree of latitude are about 30 kilometers apart.
Option A is incorrect because 10 kilometers is less than the distance between two points on the Earth that differ by 1 degree of latitude.
Option C is incorrect because 30 kilometers is the distance between two points on the Moon that differ by 1 degree of latitude.
Option D is incorrect because 50 kilometers is more than the distance between two points on the Moon that differ by 1 degree of latitude.