Observation by Chris Hooker: Mercury's tail, 30th March 2024

Uploaded by

Chris Hooker

Observer

Chris Hooker

Observed

2024 Mar 30 - 19:44

Uploaded

2024 Mar 31 - 21:41

Objects

Mercury

Equipment

William Optics ZS66 refractor
0.45x re-imaging focal reducer
Alluxa 589.3nm 2nm bandpass filter
ZWO ASI178MM camera

Exposure

45 seconds

Location

Didcot, Oxfordshire

Target name

Mercury

Title

Mercury's tail, 30th March 2024

About this image

There was cloud both above and below Mercury at the time of observation, but remarkably the planet itself remained in a band of clear sky for the 15 minutes required to capture the data for this image. The two darker stripes near Mercury are the smeared-out traces of two small strips of cirrus that drifted past. Mercury was at a nominal magnitude of 0.97, significantly reduced by extinction near the horizon, so attenuating it behind the filter strip was unnecessary. The image is a stack of 17 frames of 45 seconds exposure, with strong contrast enhancement.

Mercury's radial velocity was 9.5 km sec-1, nearly the maximum possible, resulting in strong excitation of the sodium in the tail. The angular extent of the detectable tail is 39 arc minutes, and the physical length calculated from this is 1.6 million km.

From the start of April Mercury will be too low in the evening sky for the tail to be imaged in a sufficiently dark sky, so this marks the end of the current window for observing it.

Files associated with this observation

Mercury tail 30 Mar 24 1a crop.jpg (1.4 MB)

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