The Total Lunar Eclipse of Wednesday, January 31st, 2018

The Total Lunar Eclipse of Wednesday, January 31st, 2018

This is the only eclipse of any kind (lunar or solar) visible in Idaho this year, the next being another total lunar eclipse in January of 2019.

January 31, 2018 lunar eclipse phases

Adapted from a diagram by NASA.  Note that, although the moon's orbital motion will cause it to move to the upper left relative to Earth's shadow, it (and the shadow) will be moving to the lower right (towards the western horizon) due to Earth's rotation.  Thus, for observers in the U.S., the moon will be moving lower in the sky relative to the local horizon throughout the eclipse.

Eclipse timeline (all times listed are in Mountain Standard Time (UT-7 hrs.), and rise/set/twilight times are given for Twin Falls, Idaho, USA):

  • 3:51 AM — First penumbral contact (P1).   The upper left edge of the moon begins to enter Earth's penumbral (partial) shadow.  The subtle decrease in illumination of the moon will not be noticeable to the eye.
  • 4:30 AM — Centennial Observatory opens for telescope viewing, weather permitting.  Please dress warmly!  By this time, the upper left edge of the moon should be noticeably darkened.
  • 4:48 AM — First umbral contact (U1).  The moon begins to enter Earth' umbral (full) shadow.  A small, dark "bite" begins to grow ever larger from the moon's upper left edge.
  • 5:52 AM — Total phase begins (U2) (second umbral contact).  The moon is completely immersed in Earth's umbra, appearing dark red-orange, orange-brown, or darker depending on global atmospheric conditions.
  • 6:16 AM — Start of astronomical twilight.  The first hint of pre-dawn glow begins to appear low in the east.
  • 6:25 AM — Moon too low for viewing with the Norman Herrett telescope.  Now 15° above the horizon, the moon can no longer be tracked with the observatory's 24" telescope.  Smaller telescopes will be used on the second-story Stargazers' Deck.
  • 6:31 AM — Greatest eclipse.  The moon reaches its maximum excursion into the umbral shadow, appearing at its darkest for this eclipse.  For this particular eclipse, the moon passes just south of the center of Earth's full (umbral) shadow, so it should appear fairly dark, with the lower left edge possibly appearing very subtly brighter than the upper right, which is deepest into the shadow.
  • 7:08 AM — Total phase ends (U3) (third umbral contact).  The moon begins to emerge from Earth's umbra, with a growing, bright sliver appearing at left edge of the lunar disk.
  • 7:30 AM — Observatory closes.  With the moon roughly half-way out of the umbral shadow, it will be too low to view due to the trees to the west of the observatory.
  • 7:53 AM — Sunrise
  • 7:58 AM — Moonset  The moon sets as seen from southern Idaho.  The emergence from the umbral shadow (U4, at 8:11 AM), and the penumbral shadow (P4, at 9:08 AM) occur after the moon has passed below our local horizon.