[MENTION=38859]desert-diva[/MENTION]
With a D5300, you can use the time mode or bulb mode. Set the camera to (M)anual mode and slow the shutter speed down to bulb or time. Bulb mode holds the shutter open as long as the shutter release is pressed as long as the battery doesnt die. Release the shutter button to end the exposure. The time mode allows the exposure to begin by pressing the shutter release button and ends when it is pressed again- up to 30 minutes. I suggest getting a shutter release cable to minimize the shake created by pressing, holding and releasing the shutter release button. Hope this helps.