2021, July 20: A Five-Planet Feast

When the Curves Line Up | Podcast on Spotify

July 20, 2021: The five planets are visible during the nighttime hours.  Jupiter, Saturn, and Mercury are in the morning sky.  Venus and Mars hang above the western horizon after sunset, followed by Jupiter and Saturn return to the evening sky.

2021, July 20: Jupiter and Saturn are in the south-southwest about an hour before sunrise.
Chart Caption – 2021, July 20: Jupiter and Saturn are in the south-southwest about an hour before sunrise.

by Jeffrey L. Hunt

Chicago, Illinois:  Sunrise, 5:34 a.m. CDT; Sunset, 8:20 p.m. CDT.  Check local sources for sunrise and sunset times for your location.

Morning Sky

On this day when the curves lined up 52 years ago, five planets are visible during the nighttime hours.  Jupiter, Saturn, and Mercury can be found before sunrise.  Brilliant Venus and Mars are in the western sky after sunset.  Saturn and Jupiter are slowly entering the evening sky in the southeast.

One hour before sunrise, bright Jupiter and Saturn are in the southwestern sky.  Jupiter is over one-third of the way up in the sky above the south-southwest horizon.  The Jovian Giant is the brightest star in the sky this morning.

Jupiter is retrograding in Aquarius.  This is an illusion from our faster moving planet catching up to and passing the outer planets.  Earth passes between the sun and Jupiter on August 19.

Use a binocular to spot up to four of Jupiter’s largest satellites.

Saturn is 19.6° to the lower right of Jupiter.  Saturn is among the brightest stars in the sky this morning. Only Jupiter, Mercury, Arcturus, and Vega are brighter.

Saturn is retrograding in Capricornus. It is at opposition with the sun on August 2.

Many local astronomy clubs are resuming their public activities that include telescope nights at their local observatories or in parks or other public spaces with members’ personal telescopes.  Before the weather turns colder, go to one of these public events to view Saturn through a telescope.  Seeing Saturn and its rings through a telescope is a memorable experience.  Check this link for an astronomy club near your home.

Not as bright as Saturn, the star Fomalhaut is to the lower left of Jupiter, at about the same altitude above the horizon as Saturn.

2021, July 20: Bright Mercury is low in the east-northeast before sunrise. Betelgeuse is making its first morning appearance.
Chart Caption – 2021, July 20: Bright Mercury is low in the east-northeast before sunrise. Betelgeuse is making its first morning appearance.

As the sky brightens further, Mercury is low in the east-northeast.  It is quickly slipping back into bright sunlight on its way to its superior conjunction on August 1.  This occurs when the sun is between Mercury and Earth.  Inferior conjunction occurs when Mercury is between the sun and Earth.

Mercury, it seems, is hugging the sun. It hops from one side of the sun to the other, alternating from morning sky to evening sky and back again.  From the mid-northern latitudes, it rarely (unlike others’ uses of the term for astronomy events, this means nearly never) appears in a dark sky.

At about 45 minutes before sunrise, look for Betelgeuse as it is making its first appearance, heliacal rising. It is low in the eastern sky before sunrise.

Evening Sky

2021, July 20: Through a binocular, Venus is 1.6° to the upper right of Regulus and 4.3° to the upper left of Mars.
Chart Caption – 2021, July 20: Through a binocular, Venus is 1.6° to the upper right of Regulus and 4.3° to the upper left of Mars.

Brilliant Venus continues its slow entry into the evening sky, after its first appearance nearly two months ago.  Look for it low in the west-northwest at about 45 minutes after sunset.  Tomorrow evening it passes Regulus.  The brilliant planet passed Mars on July 12.

Because Regulus and Mars are not easily seen at this level of twilight, use a binocular to spot the trio.  Venus, Regulus, and Mars easily fit into a binocular’s field of view. Venus is 1.6° to the upper right of Regulus and 4.3° to the upper left of Mars.

2021, July 20: The bright moon is 8.2° to the left of Antares.
Chart Caption – 2021, July 20: The bright moon is 8.2° to the left of Antares.

As the sky darkens a little further, the bright moon (88% illuminated) is 8.2° to the left of Antares, “the rival of Mars.”  Imagining the celestial scorpion, Antares marks the heart of the critter.

Like Betelgeuse, Antares is a very large star near the end of its stellar life.

Saturn and Jupiter are entering the evening sky.  As mentioned in the morning note, both planets are nearing their oppositions.  At opposition, the planets rise at sunset and set in the western sky at sunrise.  Leading up to opposition, the planets rise after sunset.  This evening Saturn rises 39 minutes after sundown.  Jupiter rises 93 minutes after sunset. After opposition, Jupiter and Saturn rise before sunset and are well up in the sky as evening twilight dims.

As well as a its conjunction with Regulus, tomorrow is the Venus – Jupiter opposition.  The planets are 180° apart in their orbits around the sun, compared to Earth’s location.  Venus sets as Jupiter rises.  In a week or so, both planets are visible in the evening sky simultaneously, but in opposite directions.

2021, July 20: As the calendar day ends, Jupiter and Saturn are in the southeastern sky.
Chart Caption – 2021, July 20: As the calendar day ends, Jupiter and Saturn are in the southeastern sky.

As the calendar day ends, bright Jupiter is about 19° above the southeast horizon.  Saturn is to the Jovian Giant’s upper right above the south-southeast horizon.

Detailed Daily Note: One hour before sunrise, bright Jupiter is nearly 33° above the south-southwest horizon. Retrograding in Aquarius, it is 2.0° to the upper left of ι Aqr, 4.7° below θ Aqr, and 4.8° to the lower right of σ Aqr.  Jupiter is picking up speed and beginning to reduce the gap to Saturn.  The Ringed Wonder is 19.6° to the lower right of the Jovian Giant.  Saturn is retrograding in Capricornus, 3.0° to the lower right of θ Cap. Thirty minutes later, use a binocular to find Mercury (m = −1.1) over 5° up in the east-northeast.  Forty-five minutes after sunset, brilliant Venus is over 8° above the west-northwest horizon.  It is 1.6° to the upper right of Regulus and 4.3° to the upper left of Mars.  The trio fits into a binocular field.  As the sky darkens further, the bright moon (11.0d, 88%) in the south is 8.2° to the left of Antares (α Sco, m = 1.0).  Saturn rises 39 minutes after sunset. About 70 minutes after sunset, can you find Venus low in the west-northwest and Saturn about 5° above the east-southeast horizon. Venus sets as Jupiter rises, 93 minutes after sunset.  They are at opposition tomorrow when their celestial longitudes differ by 180°.  As midnight approaches, the bright moon is nearly 20° up in the south-southwest.  Farther eastward, Saturn is over 23° above the south-southeast horizon, with Jupiter to its lower left, nearly 19° up in the southeast.

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1 reply

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