Mercury is currently in a favourable elongation for UK observers, being north of the ecliptic and visible in a fairly dark sky near the end of twilight. This image of the sodium tail is a stack of 20 30-second frames, with dark- and flat-field corrections applied during processing. An extreme contrast enhancement is still required to make the very faint tail visible.

Mercury is the bright spot behind the strip of attenuating filter on the right. The tail extends up towards the left, remaining visible to somewhere near the star at the upper centre of the image. That star is 42 arc minutes away from another star just visible above the filter strip near Mercury. The angular extent of the tail is approximately 35 arc minutes, which at Mercury's distance of 0.939 A.U. at the time corresponds to a physical length of 1.4 million km.

The excitation of the tail depends on Mercury's radial velocity, which was about 5.8 km/sec. The tail should become brighter over the next few days as the radial velocity increases. It will reach 10 km/sec on April 2nd, but by then Mercury will be too low in the sky for such observations to be possible.