Gilbert Rotary Centennial Observatory
- In the Sky for December 2017 -

Source: EVAC December Newsletter

The Moon & Planets: 

  • On Sunday, December 3, it is full Moon, so no hunting for faint fuzzies tonight. Instead, direct your attention to the bright ray system centered on Tycho which can be found many places on the Moon. Not only is it a “super” Moon (somewhat closer than usual) but also you have 2 nights to check it out (Saturday and Sunday).

  • On Tuesday, December 5, starting about 6:30 AM, you can see 3 of Jupiter's moons clustered together on the upper right side of the planet. Only Ganymede is to the lower left. Look low in the south-east for the planet (magnitude -2) and follow the dance till daylight interferes.

  • On Sunday, December 10 you can catch a shadow on Jupiter. Here is the schedule:

    • 4:35 AM Jupiter rises with Io's shadow already on it.
    • At 4:54 AM Io itself moves in front of the planet.
    • 5:56 AM Astronomical Dawn begins (light appears in the East).
    • 6:21 AM Io's shadow leaves the planet.
    • 6:27 AM Nautical Dawn begins (many stars start to fade).
    • 6:58 AM Civil Dawn begins (only a few stars are visible).
    • 7:04 AM Io itself moves from in front of the planet. At 7:26 AM the Sun rises.
  • If you want to see Io's shadow fall on Jupiter, observe the planet at 6:06 AM on December 17. If you want to see Europa’s shadow on Jupiter, the planet rises with the shadow having just fallen the planet at 3:50 AM on December 25

  • On Sunday, December 10, the Moon is at last quarter phase and rises at 1:15 AM (Monday).

  • The night of Wednesday, December 13, after midnight (Thursday), you might see some Geminid meteors. The Moon rises at 4:06 AM (Thursday) but is only 12% illuminated. Under dark skies you might see 120 meteors/hour. Look for slow, bright meteors radiating from the direction of the constellation Gemini.

  • On Sunday, December 17, it is new Moon, so you have all night to hunt for faint fuzzies.

  • On Thursday, December 21, it is the Winter Solstice in the northern hemisphere and you have the longest night of the year.

  • On Saturday, December 23, you can catch a minimum of Algol for about an hour on either side of 6:00 PM.

Evening Planets (after sunset): 

  • Mercury, SW
  • Saturn, SW
  • Neptune, S
  • Uranus, SE

Morning Planets (before sunrise): 

  • Mars, SE
  • Jupiter, SE
  • Mercury, SE
  • Venus, SE

Phases of the Moon: 

Phase Date Current Moon Info
Full Moon December 3

Description: Description: Description: Description: Click for Gilbert, Arizona Forecast

Last Quarter Moon December 10
New Moon December 18
First Quarter Moon December 26


There are no comets brighter than magnitude 8 visible this month.


The Geminid meteor shower peaks on December 13/14. Under dark skies, expect about 120 meteors per hour. The Moon will be a slim crescent, so moonlight should not significantly affect the viewing.