Observation by Paul Leyland: Themisto, or Jupiter-XVIII

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Paul Leyland


Paul Leyland


2020 Sep 05 - 22:40


2021 Jun 16 - 14:55



  • 0.4m Dilworth Relay
  • Starlight Xpress 814 Trius Pro
  • No filter

1708 s in 31 subs, stacked on mean motion of Themisto


Tacande Observatory, MPC J22

Target name

Themisto, or Jupiter XVIII


Themisto, or Jupiter-XVIII

About this image

Themisto was discovered in 1975 and subsequently lost until 2000. It is only about 9km across which makes it rather difficult to image, especially if it lies in a rich part of the Milky Way when it can very easily be hidden by much brighter stars. This image shows it in clear sky, though with an exposure time which is a little too short. Themisto is marked with cross-hairs. The only nearby star (marked with an arrow) of comparable brightness in Gaia-EDR3 is 6771111466513671680, catalogued at g=20.66. According to the JPL ephemeris, Themisto was V=20.3 at the time of observation. The marked object is exactly where predicted and of a brightness in line with the companion so I'm sure that the identification is correct.

I'll have another go in the 2021 season to see whether a clearer image can be taken.

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David Swan
David Swan, 2021 Jun 19 - 19:10 UTC

Really nice, Paul. I follow your minor satellite project with interest. I'm not able to do much astro myself at the moment due to other commitments, but I'm enjoying things vicariously - so that's a plus! David

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