More than ten years ago people started to say that it was now established beyond all doubt that large black holes (BH) exist. What exactly is the evidence? A BH is an object whose gravitational field is so strong that light cannot escape from it. This is usually thought of as part of Einstein gravity [...]
[picture by Babak Tafreshi, a member of Astronomers Without Borders] The picture is a multiple exposure taken in Rio on Monday 18 April. The questions were: (A) was the moon rising or setting? (B) what was the interval between each exposure? (C) why the the picture not include another exposure with the moon lower in [...]
The M in M101 refers to the Messier catalogue. [Photo by Takayuki Yoshida, original taken using a small amateur telescope and camera. I have rotated and cropped it to correspond with photos below. ] [Hubble photo, available in much more detail] [Processed version of Hubble image, adding in additional detail to show star-forming regions in [...]
[Part of a picture of the sun by Alan Friedman] The dark area on the surface of the sun is a “sunspot”. The image uses false colours and is mainly taken in H-alpha light to pick up the “detached prominence” more clearly. The NASA image above shows a more typical prominence with superimposed images of [...]
It is surprisingly difficult to discover even basic things about the star population of the Galaxy (the one we are in – the Milky Way). For example, what proportion of stars are single (as opposed to binary or multiple)? It used to be thought that most stars were binaries, but it was later realized that [...]
