Every “spot” on Earth has a corresponding “spot” in the sky. For instance, on the spot where you are now, directly overhead, is the zenith. There is only one zenith where you stand. No two spots share the same zenith. Every spot on a sphere “points to” a different location in the sky. Nobody shares your zenith.
Your Zenith is Unique
Imagine the boundary of your country as a set of these spots. These locations can be projected onto the celestial sphere. Projecting shapes of countries onto the sky can help you really “see” how large or small a country is. Seeing countries from the inside out helps to understand the shape of the Earth as a sphere.
That Star is Someone’s “First Star I See Tonight.”
When you see a star rising you are actually seeing a star that someone 6 timezones east of you sees directly overhead.
Sirius rises just before dawn (heliacal rising) in mid August (at latitude 40˚N). It rises earliers and earlier each day until by November it is rising at midnight. When people on the east coast of the USA see Sirius rising, people in Western Europe see the same star Sirius high in the sky at the meridian.
This hilariously-headlined New York Times article describes the results of the observational experiment performed during the 1919 eclipse. It highlights that the expedition proved Einstein’s prediction. But the writer claims that only 12 men on Earth can really understand the result: that light’s path is curved by space time.
I just received this wonderful message from a group of students in Japan (thanks to Patricia McGahan for providing the connection!) who are learning and teaching about the Japanese Hayabusa2 mission to the Ryugu asteroid.
(Welcome to Japanese language visitors and link to Japanese Wikipedia page.)