This episode focuses first on explaining light-years. It then changes it's focus by doing a repeat of the calendar year they also did in the pilot, but in a different way.
The also explain the Speed of Light, and other scientific theories. This episode goes into detail of these theories instead of a mere overview.
Then they focus on gravity, and what would happen if the Earth become gravity-less, that in turn would create a black hole.
Then the TARDIS pays a visit to the nearest black hole, Cygnus X1.
Overall a great episode, this gets an 8 out of 10.
The also explain the Speed of Light, and other scientific theories. This episode goes into detail of these theories instead of a mere overview.
Then they focus on gravity, and what would happen if the Earth become gravity-less, that in turn would create a black hole.
Then the TARDIS pays a visit to the nearest black hole, Cygnus X1.
Overall a great episode, this gets an 8 out of 10.