Mercury’s sodium tail captured early in the morning of the 14^th. Due to time restrictions I decided not to position Mercury behind the occulting strip seen at the left. The camera was accidentally installed in the wrong orientation, so the tail extended towards the strip, rather than away from it as intended! As the tail was very undeveloped and relatively short, fortunately it did not reach the strip.

The image is a stack of 11 frames of 45 seconds exposure. An extreme contrast stretch was needed to make the very faint tail visible, and Mercury is heavily saturated as a result. The bright star at bottom centre of the image is kappa Virginis, which was 48.7 arc minutes away from Mercury. The extent of the detected tail was 6 arc minutes. The other bright spot at lower right is a ghost reflection of Mercury.

Mercury was just short of four days past perihelion, which occurred at 0836 UT on the 10^th. This image marks a very early stage in the development of the tail, which occurs as Mercury’s radial velocity increases after perihelion and solar radiation pressure drives sodium away from the planet. On the 14^th Mercury’s radial velocity was 4.16 km s^-1 and the True Anomaly Angle was 24.45 degrees; that is the angle Mercury has moved round its orbit since perihelion. The smallest TAA of any previously-published image of the tail was around 28 degrees.