How can we focus radio telescopes on a star when the earth is spinning?

There are two processes to manage this:

First, the telescopes (really, big antennas) are aimed mechanically and move so they can maintain their reception of a specific star/source/sky location over time.

However, except for stars immediately in the vicinity of the pole stars, the star will eventually go below the horizon. Once this happens the telescope/antenna cannot receive anything further until the source appears above the horizon again.

What happens at this point is we have many telescopes/antennas around the world that are collectively controlled. Long before a star/source/etc falls below the horizon for one telescope, another telescope further west has already pointed at it, and is receiving the same signal. Once this switchover has occurred, the previous telescope is free to select another target - something else on the other side of the planet that will be falling below the horizon for telescope further east.

In this way:

• The telescopes are under constant use pointing at interesting things


• Things which need continuous monitoring can be monitored without interruption despite the world turning


• We can observe anything at any time, as long as there's available time on the radio telescope network


• Sharing resources allows scientists to conduct science more completely and inexpensively


• By having 2 or more telescopes pointing at the same object at once, we can effectively increase the signal to noise ratio and get better data - it's technically very similar to having one earth sized single antenna rather than two tiny (relatively) antennas.


• With central control of a whole participating worldwide network, scientists can react very quickly to sudden phenomena, like bursts, at any time, regardless of the position of the earth