2021, April 13: Jupiter, Saturn Race Along Ecliptic Highway

2021, April 13: Morning Planets Jupiter and Saturn are in front of the stars of Capricornus.
2021, April 13: Morning Planets Jupiter and Saturn are in front of the stars of Capricornus.

April 13, 2021: One hour before sunrise, Jupiter and Saturn are low in the southeastern sky.  They are moving eastward in Capricornus.  Use a binocular to make daily observations of the eastward drive.

by Jeffrey L. Hunt

Chicago, Illinois:  Sunrise, 6:13 a.m. CDT; Sunset, 7:30 p.m. CDT.  Check local sources for sunrise and sunset times for your location.

Before sunrise, Saturn is 16.0° up in the southeast.  Bright Jupiter is 13.3° to the lower left of the Ringed Wonder.

Use a binocular to note the places of Saturn and Jupiter compared to the starry background.  Saturn is 1.8° to the upper right of Theta Capricorni (θ Cap on the chart).  Jupiter is 2.5° to the upper left of Deneb Algiedi, “the kid’s tail” (δ Cap), and 0.5° to the upper right of Mu Capricorni (μ Cap).

In two mornings, Mu Capricorni seems to intermingle with Jupiter’s moons.  While the star is farther away, the star and the planet’s moons appear along the same line of sight, like the rising sun near buildings at the horizon. Get your spotting scope or small telescope ready to observe Jupiter, its moons, and the distant star together.

During the next several mornings watch these giant planets move eastward compared to the starry background.

The planets seem to move along an imaginary line in the sky, known as the ecliptic.  The planets move nearly in the same plane like that of a pancake, with the sun at the center.  Since our planet is in that pancake, we see the planets elsewhere in the pancake, but along the thin height of the breakfast treat.

From the northern hemisphere the planets move along their paths toward the east, that’s from right to left as we face southward.  Each day the earth’s rotation causes them to rise in the east and set in the west, but their orbital motion is eastward.

Detailed Note: One hour before sunrise, Saturn is 16.0° up in the southeast.  Jupiter continues to slowly move away from the Ringed Wonder.  This morning the gap is 13.3°.  The Jovian Giant is over 11° above the east-southeast horizon.  Use a binocular during several mornings to estimate the speed of each planet compared to the starry background.  The changes are small but noticeable when observed across several mornings.  This morning Saturn is 1.8° to the upper right of θ Cap.  Jupiter is 2.5° to the upper left of Deneb Algiedi and 0.5° to the upper right of μ Cap.  Thirty minutes after sunset, the moon (1.9d, 3%) is nearly 12° up in the west. Thirty minutes later, it is less than 7° in altitude.  At this time, Mars is less than halfway up in the west between the horns of Taurus.  It is above a line from Elnath to ζ Tau.  The planet is 4.1° to the upper left of Elnath and 3.7° to the upper right of ζ Tau.

Read more about the planets during April 2021.


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