Home > Ephemeris Program, Star Clusters > 10/28/2014 – Ephemeris – The Pleiades Distance Controversy

10/28/2014 – Ephemeris – The Pleiades Distance Controversy

October 28, 2014

Ephemeris for Tuesday, October 28th.  The sun will rise at 8:14.  It’ll be up for 10 hours and 22 minutes, setting at 6:37.   The moon, 2 days before first quarter, will set at 10:37 this evening.

Yesterday we looked at the Pleiades or Seven Sisters star cluster.  The Pleiades is nearby.  For a long time the Pleiades distance was calculated to be about 435 light years.  It was beyond the distance that could be determined from the Earth by triangulation or parallax.  In the early 1990s the European Space Agency satellite Hipparcos was launched to improve and extend the parallax measurement of nearby stars.  However the distance determined to the Pleiades was 392 light years, 90 percent of the previous value.  A lot of what we have determined about stars and their evolution was based on the original distance to the Pleiades.  It meant that the Pleiades stars were  dimmer than first calculated, affecting our ideas of stellar evolution.  Many astronomers were wary of the supposed more accurate Hipparcos result.  However recently using a network of radio telescopes that span the diameter of the Earth in a Very Long Base Interferometry Array, a new distance was determined, a more agreeable 444 light years.

Times are for the Traverse City/Interlochen area of Michigan.  They may be different for your location.


The Pleiades, about what you'd see in binoculars.

The Pleiades, about what you’d see in binoculars.


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