What interested her most was the longitude line.

她最感兴趣的是那条通过天文台的经线。

Longitude lines go, if you will, from north to south.

经度线，如果你愿意的话，从北到南。

It's called Greenwich, England, and that is the zero degree longitude line, and then you can count up to 180 degrees east and west from there.

它叫做英国格林威治， 那是零度经线，然后你可以从那里数到东西180度。