Verified answer

The effect is called star trails. Up to a 30-second exposure, stars will still look like pin points, especially when photographed with a wide-angle lens.

Beyond 30 seconds, and the light from the stars will begin to smear, especially if you use a telephoto lens.

To make star trails, you can either take one hours-long exposure, or take many, many short 30-second exposures and then blend them all into one shot using software.

Here's a link to 500px.com showing star shots. Click on an image to open it up, and then click on the details tab on the right which often will show the camera, lens and exposure used. https://500px.com/search?q=star+trail&submit=Submi...

To add to fhotoace's comment, you can take a lot of shorter exposures (30sec) and combine them later in a stacking program or photo editor, e.g. link. This can help reduce sensor problems for very long exposures as well as giving the chance to selectively edit to stop overexposure of fixed landscape within the photo when stacking. You may be talking several hours to get long trails, though. It also lets you change batteries (carefully), should the need arise if you don't have an external battery pack. This is more of an issue if it's cold where battery life can be shorter.

Long exposure.

One sets up the camera/phone on a tripod or other rigid mount and opens the shutter for minutes at a time. The opening normally has to be fairly small and aim avoids other sources of light that over expose. The length of the arc depends on the minutes open. Some cameras don't have a setting to push once to open, push again to close and holding the shutter with B (bulb) setting gets really awkward.

Long exposure.

Long exposure.