Terra SAR X and Tandem X flying in formation (and flaring!)
This provides a very nice sight for observers, especially since both satellites also produce slow, naked eye flares when the sun-satellite-observer angle is favourable.
Yesterday evening near the end of twilight, I had a favourable pass, with the duo cruising through the zenith at an altitude of around 515 km. They flared while they did this, to mag. +1, at about 17:01:15 UTC (28 Nov), give or take a few seconds. My camera opened just a few seconds after the flare peak, and captured the pair while slowly fading in this 10 second image:
Movement is from bottom right to upper left. I measure a distance of 70 arcseconds (or just over 1 arcminute) between the two objects on this image, corresponding at face value to about 175 meter distance. But because there is a small altitude difference between the two objects as well, the true separation between the two is a bit more than this value. Terra SAR X (2007-026A) is the slightly leading and slightly brighter object in the formation.