Daniel Fischer<p>50 years ago today, at 16:09 UTC on 17 July 1975, the Apollo-Soyuz Test Project culminated in the first docking of the spacecraft - but afterwards an interesting experiment took place: after they separated again Apollo (the final one; no number) occulted the Sun from the point of view of Soyuz 19. Images obtained show mostly outgassing from Apollo forward-scattering light from the hidden Sun but allegedly there is also some outer corona in the images of which <a href="https://www.esa.int/ESA_Multimedia/Images/2010/04/Artificial_eclipse_produced_by_US_Apollo_spacecraft" rel="nofollow noopener" translate="no" target="_blank"><span class="invisible">https://www.</span><span class="ellipsis">esa.int/ESA_Multimedia/Images/</span><span class="invisible">2010/04/Artificial_eclipse_produced_by_US_Apollo_spacecraft</span></a> shows one with a negative caption. The planned artificial <a href="https://scicomm.xyz/tags/eclipse" class="mention hashtag" rel="nofollow noopener" target="_blank">#<span>eclipse</span></a> experiment was described in the mission press kit <a href="https://www.nasa.gov/wp-content/uploads/static/history/astp/documents/astp%20press%20kit%20(us).pdf" rel="nofollow noopener" translate="no" target="_blank"><span class="invisible">https://www.</span><span class="ellipsis">nasa.gov/wp-content/uploads/st</span><span class="invisible">atic/history/astp/documents/astp%20press%20kit%20(us).pdf</span></a> on PDF pages 37-39 and the outcome is discussed in the didactical NASA brochure <a href="https://ntrs.nasa.gov/api/citations/19780019206/downloads/19780019206.pdf" rel="nofollow noopener" translate="no" target="_blank"><span class="invisible">https://</span><span class="ellipsis">ntrs.nasa.gov/api/citations/19</span><span class="invisible">780019206/downloads/19780019206.pdf</span></a> on PDF pages 20-27; there is apparently also a more technical paper in a mission science report but I couldn't find that one online.</p>