How can you look at the sun through a telescope without hurting your eyes?

Question: How can you look at the sun through a telescope without hurting your eyes?
- Keywords:
  sun,
  telescope
Asked by Alex and Robert to Tim on 8 Mar 2018. This question was also asked by 547spdm26.
- Tim Duckenfield answered on 8 Mar 2018:
  
  The telescope has a special “filter”, which means it only lets through a tiny amount of the light that hits the telescope. All this light is roughly the same colour too, so if you ever get a chance to look through my “H-alpha” telescope at the Sun, it looks red. That is because it is only letting through a little bit of the red light, to protect our eyes.

Question: How can you look at the sun through a telescope without hurting your eyes?