Caroline Morley, online picture researcher
(Image: NASA, DOE, International Fermi LAT Collaboration)
When dancers spin on the spot, they choose a point in front of them and try to keep their eyes fixed on it for as much of the spin as possible.
It can't be so easy to keep the Fermi Gamma-ray Space Telescope trained on one spot in the sky as it maps the universe. Fermi orbits the Earth every 95 minutes while rocking between the north and the south on alternate orbits, On top of this, the satellite also completes one rotation every 54 days to keep its solar panels facing the sun.
This image traces Fermi's view via its Large Area Telescope of the gamma rays emitted by the Vela pulsar from August 2008 to August 2010. The Vela pulsar is a neutron star, itself spinning at a dizzying 11 times per second and the brightest and most persistent source of gamma rays in the sky, giving an anchoring point for Fermi's own spin.