Southern Colorado Skies / March 18-24, 2018

Consider a planetarium program to help you plan your observations. There are many commercial products available; an excellent program (STELLARIUM) is available free at


Venus and Mercury are still visible this week in the west shortly after sunset. Look for the waxing crescent Moon to join the party early in the week.

The Moon waxes toward first-quarter all week (it occurs on Saturday), so this is a perfect opportunity for you to have a look. In my photo below you can clearly see the dark (lava-covered) Mare Serenitatis (“the Sea of Serenity”) near the top, with Mare Tranquilitatis (“the Sea of Tranquility”) in the center, and Mare Crisium (“the Sea of Crises”) on the right.

At or near first quarter, the Sun shines obliquely on the Alps, Caucasus and Apennine Mountains to the north, and many interesting craters and other formations to the south. The terminator (the imaginary line that separates light and dark) indicates sunrise on the Moon as it waxes towards its full phase, and like on Earth this is a region where deep shadows show a lot of contrast and detail. First and last quarters are prime opportunities for observing the Moon.

Sunday (March 18)

During a brief time after sunset, Venus and Mercury are visible to the right of the thin crescent Moon (see above graphic).

Monday (March 19)

The Moon continues its dance at sunset with Venus and Mercury (see above graphic).

Tuesday (March 20)

Vernal (spring) equinox occurs at 10:15 a.m. MDT, with 12 hours and 11 minutes of daylight.

Why not 12 hours exactly?

Sunrise officially occurs when the upper edge of the Sun’s disk becomes visible above the horizon (rather than using the center of the Sun, as you might expect). Later at sunset, the same reference point is used: sunset occurs when the Sun’s upper edge disappears below the horizon. Therefore, the time required for the sun to fully rise and set is added to the total daylight for the day, resulting in the day lasting several minutes longer than 12 hours.

The Moon continues its dance at sunset with Venus and Mercury (see above graphic).

Saturday (March 24)

First-quarter Moon occurs at 9:35 a.m. MDT.




Mercury and Venus (both in Pisces)

Mercury and Venus appear together shortly after sunset (see above graphic). Fainter Mercury get dimmer as the week progresses. Look for Mercury to the upper right of Venus early in the week, to the right of Venus by Wednesday, and to the lower right of Venus by week’s end.

Mars and Saturn (both in Sagittarius)

Both planet rise about 3 a.m. and are in good viewing position well before dawn, above the “teapot” in Sagittarius. Mars continues to get closer to Saturn from our vantage point on Earth: 8.5 degrees apart on March 17th down to 5 degrees on March 24th; they will be their closest (1.3 degrees) on April 2nd.

Jupiter (in Libra)

Jupiter rises before midnight and dominates the southern sky for the rest of the night. It’s in its best position for observation between 4 and 5 a.m.

Uranus (in Pisces) and Neptune (in Aquarius)

Both planets are now lost in the glare of the sunset.


The following data are based on my location in Pueblo West, Colorado. If you live well outside this area, you should consider checking this information for your location in order to be assured of accurate times, elevations, etc. If you’re unfamiliar with Iridium flares, check out my short article at:

Sunday (March 18) 8:39:23 p.m. / Magnitude -2.1 / N / Elevation 31 degrees

Monday (March 19) 8:33:10 p.m. / Magnitude -7.3 / N / Elevation 33 degrees


These are too numerous to list here! If you’re seriously interested, load the ISS DETECTOR app on your smart phone or tablet.

Carpe noctem

Dave Furry

Pueblo West, Colorado

One thought on “Southern Colorado Skies / March 18-24, 2018

  1. Pingback:

Leave a Reply