An intervalometer that plugs into the remote shutter release connector of the camera, or else tether the camera to a PC by USB cable and use an app like DigiCamControl.
The intervalometer option is versatile and not that expensive. You can use it to make time-lapse series also, which is the original purpose of the devices. Can also use as a straight remote shutter release. And setting the camera to bulb mode allows you to program a long exposure time of your choosing with just the 1 press of the button.