The edge of space is commonly defined as the Karman line, an altitude of 100 kilometres (about 62 miles) above sea level, recognised by the world air sports federation FAI as the boundary between Earth's atmosphere and outer space. Above it the air is too thin for conventional aircraft to generate lift.

Most modern fighter jets have a service ceiling around 15,000 to 20,000 metres (roughly 50,000 to 65,000 feet). The Russian MiG-29 climbs especially high, which is why it is used for edge-of-space experience flights. The all-time record was set by a MiG-25, which reached over 37,000 metres.

Yes. Companies such as MiGFlug offer edge-of-space flights in the MiG-29, climbing to over 20,000 metres (around 66,000 feet) where the sky turns dark and the curvature of the Earth becomes visible. It is the closest a civilian can get to space in a jet aircraft. You can see what a MiG-29 flight costs here.

At very high altitude the atmosphere is so thin that very little sunlight is scattered, so the sky above appears deep blue to black even in daytime. From around 20,000 metres pilots can see the curvature of the Earth below and the blackness of space above, an experience usually reserved for astronauts.

The Karman line is the internationally recognised boundary of space, set at 100 kilometres altitude. It is named after engineer Theodore von Karman, who calculated the height at which the atmosphere becomes too thin for aerodynamic flight. People have also reached the edge of space by balloon, such as Joe Kittinger's record 1960 jump.