2021, April 19: Moon, Twins, Mars, Evening Watch

April 19, 2021: Venus begins to appear in the west after sunset.  The moon lines up with Pollux and Castor, while Mars is above Bull’s horns in the western evening sky.

by Jeffrey L. Hunt

Chicago, Illinois:  Sunrise, 6:04 a.m. CDT; Sunset, 7:36 p.m. CDT.  Check local sources for sunrise and sunset times for your location.

Venus begins its evening apparition.  Find it low in the west-northwest about 20 minutes after sunset.

Read more about Venus in our summary document.

One hour after sunset, the nearly half-full moon is over two-thirds of the way up in the sky in the southwest.  It is 5.0° to the lower left of Pollux, a Gemini Twin.  Notice that the moon, Pollux, and Castor appear along the same imaginary line.

At this time, Mars is less than halfway up in the west.  It is above the Bull’s horns, Elnath and Zeta Tauri (ζ Tau on the chart).  This evening the Red Planet is 4.6° to the upper right of Zeta Tauri.

In five evenings, Mars moves into Gemini.

Here’s more about Mars during 2021.

Read about Mars during April.

Detailed Note: One hour before sunrise, Saturn – nearly 18° above the southeast horizon – is 1.5° to the upper right of θ Cap.  Jupiter (m = −2.2) – over 13° up in the east-southeast – is 13.9° to the lower left of Saturn.  In the starfield, Jupiter is 3.3° to the upper left of Deneb Algiedi, 0.4° to the lower left of μ Cap, and 2.8° to the upper right of Iota Aquarii (ι Aqr, m = 4.3).  Use a binocular to find the starry background and to observe Jupiter’s eastward trek compared to it.  In six mornings, Jupiter crosses into Aquarius. Twenty minutes after sunset, Venus (m = −3.9) is making its first naked-eye evening appearance. This prediction is from factors described by Jean Meeus’ book, Mathematical Astronomy Morsels.  Find it about 2° up in the west-northwest. In a darker sky, forty minutes later, the moon (8.0d, 48%) is over two-thirds of the way up in the southwest.  It is 5.0° to the lower left of Pollux.  The half-full moon, Pollux, and Castor (α Gem, m = 1.6) are in a line.  Meanwhile, farther west, Mars is about 40° up in the west.  It is 4.6° to the upper right of ζ Tau.

Read more about the planets during April 2021.