January 2018 Skygazing from the Robert Ferguson Observatory Featured

The moon is very "active" this month, with two full moons, both associated with large tides and the first full moon at the start of the month being the largest of 2018. There is a total lunar eclipse of the second full moon! The moon occults a number of bright stars and has many close pairings with planets and colorful bright stars. Plus, we have some nice chances to spot very thin crescent moons.

Mars has a nice close encounter with the bright wide double-star Zubenelgenubi in Libra at the start of the month, then passes very near Jupiter. Mercury continues a nice morning apparition, joined by Saturn as it rises from the sunrise glare a few days before Mercury disappears, with the two very close together on the morning of 1/13.


 [Note: All times are local Pacific Time and calculated for the RFO site.]

* Use the "What's Up in the Night Sky" link on our website for additional events and details.

Moon - The "Wolf" full moon on the evening of 1/1 is the largest full moon of 2018 and occurs just 4 hours before a very close perigee, thus causing extremely large tides from about 1/1 to 1/4. This is the third of a series of three months with large tides following the full moon. Around midnight on the evening of 1/4 the moon is very near the bright blue star Regulus in Leo; use binoculars. Last Quarter is on the afternoon of 1/8. Look for the crescent moon near Jupiter and Mars around 4am on 1/11. The crescent moon is near Saturn and Mercury low in the southeast 45 minutes before sunrise on 1/14 and 1/15, with a thin 2.1% crescent on the 15th. New moon is on the evening of 1/16. See if you can spot the ultra-thin 0.8% crescent moon 5° high and 28° south of due west 20 minutes after sunset (or at about 5:36pm calculated for RFO) on 1/17. You will need to use binoculars. The next evening a 3.6% crescent moon should be easy to spot around 6pm. First Quarter is on the afternoon of 1/24. That evening the moon will occult the bright star xi-2 Ceti (see below). The moon will occult the star 75 Tauri shortly after midnight on the evening of 1/26 (see below). Look for the moon very near the bright red-orange star Aldebaran in Taurus around 2am on 1/27 (the same morning as the preceding occultation), with the two drawing ever nearer as the moon sets around 3:18am. Use binoculars to enjoy the color. The moon occults the two bright stars 119 and 120 Tauri on the morning of 1/28 (see below). Finally, there is a second full "blue" moon this month on the morning of 1/31, when there is also a total lunar eclipse (see below). This is the last of the sequence of full moons causing large tides, from about 1/31 to 2/2. Also, February will have no full moon this year. February's moon is known as the "Snow" moon, so perhaps this is the "Blue Snow" moon! (Note: There are also a few slightly more challenging lunar occultations this month, with details on our website.)

Mercury - Mercury continues its very good morning apparition from last month until about 1/15. It was at a maximum altitude of 10° 45 minutes before sunrise on 12/29. Greatest elongation west is on 1/1. It is near Saturn during the last few days, drawing very near on the morning of 1/13, with both joined by the crescent moon on 1/14 and 1/15.

Venus - Venus is at superior conjunction (far side of the sun) on 1/8 and so not viewable this month.

Mars - In Libra, Mars rises around 3am and is very near the bright wide double star Zubenelgenubi at the start of the month, with Jupiter near this pair. Mars draws very near Jupiter on the morning of 1/7. The crescent moon joins Mars on the morning of 1/11. Mars moves into Scorpius late in the month.

Jupiter - Jupiter, in Libra, is near Mars as the month begins, with the two closest on the morning of 1/7 and the crescent moon nearby on 1/11. Jupiter rises around 2:30am mid-month.

Saturn - Saturn, in Sagittarius, is just past conjunction with the sun and emerges into the predawn twilight mid-month, passing near Mercury from about 1/10 to 1/15 with the pair very close together on 1/13, then joined by the crescent moon on 1/14 and 1/15.

Uranus - In Pisces, Uranus is now a few months past opposition and ends retrograde motion on 1/2. It is still a good scope or binocular target in the evening sky for a bit longer, setting around 12:30am mid-month.

Ceres at Opposition - The dwarf planet Ceres is at opposition in Cancer around 5am on 1/31. It will be at magnitude 6.9 and about 1° WNW of the star tau Cnc (RA9h14.1m; Dec+30.03°). Use a finder's chart.

Total Lunar Eclipse - The moon passes through earth's umbral shadow on the morning of 1/31. Darkening should start to become evident around 3:30am.

Here is the sequence of events locally:

0252 Moon enters penumbra

0349 Moon enters umbra

0452 Start of totality

0545 Start of astronomical twilight

0607 End of totality

0710 Moon exits umbra

0716 Sunrise

Quadrantid Meteor Shower - Conditions are poor this year, alas, for this otherwise always active meteor shower that has rates of from 60 to 200 or more meteors per hour at peak. The peak is predicted for early afternoon on 1/3 and a nearly full moon will interfere with meteor observing all night. Still, for those determined, the evening of 1/3 and a.m. hours of 1/4 should be best.

Occultation of xi-2 Ceti - At about 7:53pm on 1/24 the magnitude 4.3 star xi-2 Cet will disappear behind the moon's dark limb 28° from the south cusp. (Calculated using Occult4 for the RFO site. Details will differ as distance from RFO increases and no occultation may occur for those far away.)

Occultation of 75 Tauri - At about 12:15am on 1/27 the magnitude 5.0 star 75 Tau will disappear behind the moon's dark limb 59° from the south cusp. (Calculated using Occult4 for the RFO site. Details will differ as distance from RFO increases and no occultation may occur for those far away.)

Occultation of 119 & 120 Tauri - At about 1:29am on 1/28 the magnitude 4.3 star 119 Tau will disappear behind the moon's dark limb 57° from the south cusp. Then, at about 2:07am, magnitude 5.7 120 Tau does likewise 44° from the south cusp. This second event is slightly more challenging and requires somewhat larger aperture scopes. (Calculated using Occult4 for the RFO site. Details will differ as distance from RFO increases and no occultation may occur for those far away.)

Algol Eclipses - The sky position and long nights of fall and winter make this the best time to observe the famous eclipsing variable star Algol (beta Persei) in Perseus. The orbital plane of this close pair of stars coincides with our line of sight. Once every orbit the dimmer star eclipses (actually, occults) the brighter star and the light we see from what appears to us as a single star grows dimmer. This happens every 2 days 48 minutes 56 seconds. The eclipse lasts about 10 hours, though the most obvious dimming lasts about 6 hours, centered around the eclipse minimum. Normally, Algol is at magnitude 2.1 (similar in brightness to the North Star) but dips to magnitude 3.4 at eclipse minimum. Algol is in a trapezoid arrangement with 3 other stars: pi, rho and omega Persei. Most of the time Algol is much brighter than the other 3 stars. However at eclipse minimum it is the same brightness as rho Persei, the star diagonally opposite Algol in the trapezoid. Use binoculars to help observe these 4 stars easily. The nearby star gamma Andromedae, at magnitude 2.2, can be used as a reference for Algol at its normal brightness. Convenient eclipse minimum times are listed below. Those in early evening allow for watching Algol return to normal brightness after minimum. Those in morning hours allow watching Algol dim before minimum.

Algol minima:

1/04 5:02am

1/07 1:51am

1/09 10:40pm

1/12 7:29pm

1/27 3:33am

1/30 12:22am


Capitalized items refer to the sections above.

12/19 to 1/15 - MERCURY in the east

1/01 to 1/04 - Extremely Large Tides due to Full MOON very near perigee

1/01 - "Wolf" Full MOON

1/02 - URANUS ends retrograde motion


1/04 - ALGOL ECLIPSE minimum

1/05 - MOON very near Regulus

1/07 - ALGOL ECLIPSE minimum

1/07 - MARS very near JUPITER

1/08 - Last Quarter MOON

1/08 - VENUS at superior conjunction

1/09 - ALGOL ECLIPSE minimum

1/11 - Crescent MOON near JUPITER and MARS

1/12 - ALGOL ECLIPSE minimum

1/13 - MERCURY very near SATURN

1/14 - Crescent MOON near MERCURY and SATURN

1/15 - 2.1% Crescent MOON near MERCURY and SATURN

1/16 - New MOON

1/17 - 0.8% Crescent MOON in west

1/18 - 3.6% Crescent MOON in west

1/24 - First Quarter MOON



1/27 - MOON very near Aldebaran

1/27 - ALGOL ECLIPSE minimum

1/28 - OCCULTATION OF 119 & 120 TAURI

1/30 - ALGOL ECLIPSE minimum

1/31 to 2/02 - Large tides due to Full MOON near perigee



1/31 - Full "Blue" MOON


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