1623: The Great Conjunction of Jupiter and Saturn

The Starry Sky
(NASA Photo)

The 2020 Great Conjunction of Jupiter and Saturn is the closest conjunction of these giant planets since the conjunction of them in 1623.

Was this conjunction observed?

The Jupiter – Saturn conjunction of 1623 occurred in the wake of the invention of the telescope, so observing was in its infancy; yet, the sky was full of planetary activity. A partial lunar eclipse (April 15, 1623) was visible throughout the Americas and in Central Europe, where the moon was setting as the eclipse reached its 90% magnitude. Venus passed Jupiter and Saturn in late June and Mercury passed the planetary pair less than two weeks later, when the planets were about 22° east of the sun. With the inner planets in the vicinity of the impending Great Conjunction and Mars reaching opposition (July 4, 1623), surely sky watchers were observing the planets’ locations to test and revise their planetary motion equations.

By the time of the Great Conjunction on July 16, 1623, the planetary pair was less than 13° east of the sun. By Civil Twilight, the pair was near the horizon at mid-latitudes. Without optical help, the conjunction likely went unobserved, even for those with recently minted telescopes. Even then, the observer needed some luck to find the conjunction.

In later years, two British publications stated that the 1623 conjunction was not observed. In 1886, the Monthly Notices of the Royal Astronomical Society state that the February 8, 1683, Jupiter – Saturn conjunction was the first observed “since the invention of the telescope” and that the 1623 passing went unobserved. The same statement was written in the Journal of the British Astronomical Association in 1897. Perhaps the conjunction was observed without optical aid and recorded from more southerly latitudes, when the planets were higher in the sky.

Did the two British publications make the statements out of parochialism, rather than from factual observations made around Europe regarding the first Great Conjunction observed with a telescope, or was this the first time that the conjunction fit into an eyepiece since the telescope’s invention? The February 24, 1643, conjunction was visible in the western sky during mid-twilight as well as the October 16, 1663, conjunction. At the second conjunction the planets were about 10° up in the southwest at one hour after sunset. However, at both conjunctions, the planets were nearly 1° apart. At the 1683 conjunction, the planets were close, about 0.2° apart, twice the separation of the upcoming event. While the two previous conjunctions were visible to the naked eye and individually in a telescopic eyepiece, the 1683 conjunction was the first observed with both planets simultaneously in an eyepiece. With a separation of 0.1°, the 1623 conjunction would have fit into telescopes eyepieces of that generation, but certainly those early telescopes were unwieldy to steer and hold steady, and the telescope operator needed some persistence during the days preceding the conjunction to follow the converging planets into bright twilight while they had sufficient altitude to observe them. So, while the British publications are accurate about viewing the planets simultaneously through a telescope, the two preceding conjunctions were visible to the unaided eye and individually through a telescope, and this does not speak to the issue as whether the 1623 conjunction when unobserved across all of humanity.

In recent times, Great Conjunctions occurred February 18, 1961; followed by a triple conjunction of the two planets in 1980-81; and the last occurred May 30, 2000, although this was difficult to observe.

Read the Great Conjunction of 2020 Article.

2020, February 14: Morning Planets Jupiter and Mars

Jupiter and Mars, February 14, 2020In a cold, clear sky with a gibbous moon, morning planets Jupiter and Mars shine from the southeastern sky.  Jupiter and Saturn are emerging from their recent solar conjunctions and heading for their Great Conjunction later in the year.

This morning,  Mars is nearly 18° to the upper right of Jupiter.  During the next 5 weeks watch Mars march eastward compared to the starry background and pass Jupiter on March 20 and Saturn, March 31.

Link to summary about February 2020’s morning planets.

Here’s the detailed note for this morning:

  • February 14: One hour before sunrise, the moon (20.6 days past New, 66% illuminated), nearly 36° up in the south-southwest is midway from Spica to Zubeneschamali (β Lib, m = 2.6) and about 2° to the left of Kappa Virginis (κ Vir, m = 4.2). Use a binocular to locate the dimmer stars this morning. Jupiter passes Pi Sagittarii (π Sgr, m =2.9), 1.4° to the lower right of the star. Mars is nearly 18° to the upper right of Jupiter, 1.6° to the upper right of 4 Sagittarii (4 Sgr, m = 4.1) – the western gateway to the bright nebulae in Sagittarius. Watch Mars move through this region during the next several mornings. The challenge is to find a reasonable time to view Mars among the nebulae so that it has enough altitude, but when the sky is still dark enough to find the faint clouds.  Forty-five minutes before sunrise, Jupiter is over 10° in altitude in the southeastern sky. Saturn is about 10° to Jupiter’s lower left, nearly 6° in altitude.

2020, March: Venus Brilliant Evening Planet

Venus moves past a galaxy and the planet Uranus

Venus is the bright planet shining in the west. Early in the month, Venus passes two celestial objects that are dim to the human eye. Use a binocular to see it pass a galaxy and the planet Uranus.

Link to Venus during March 2020 article.

On March 3, look for the brilliant planet about 4 degrees to the left of the galaxy. Holding a binocular steady, put Venus on the lower left side of the view. A cloudy oval with a starlike center, appears to the upper right of the view.

On March 7, brilliant Venus appears to the right of Uranus.  Uranus’ brightness is at the limit of human eyesight.  Through a binocular, it appears as a bluish star.  Put Venus to the right side of the binocular’s view. Uranus will appear to the left of Venus left of center of the view.

For more details about seeing the galaxy and the planet Uranus, see the daily notes that follow that match the dates on the chart above.

  • March 3: One hour after sunset brilliant Venus is over 30° in altitude in the west-southwest. It passes 4° to the lower left of M74 (NGC 628, m = 8.8, 8’ apparent size). Mallas in The Messier Album, describes the view, “This is a difficult galaxy for a 4” refractor, but it is easily seen in the 10 x 40 finder. A casual observer might miss this object completely, for the central condensation is starlike and the outer parts have very low surface brightness” (p. 146). Also look for Uranus, 5.3° to the upper left of Venus. 
  • March 4: One hour after sunset, Venus is over 30° up in the west-southwest. It moves into Aries, 4.3° to the lower right of Uranus.  
  • March 5:  One hour after sunset, brilliant Venus is over 30° up in the west-southwest, 3.5° to the lower right of Uranus. Through a telescope, Venus is 61% illuminated – an evening gibbous – and 20” across. 
  • March 6: One hour after sunset, the bright moon (12.4d, 90%), nearly 50° up in the east-southeast is in the middle of Cancer’s dim stars nearly midway from Pollux and Regulus (α Leo, m =1.3). At the same time, Venus is over 30° up in the west, 2.7° to the lower right of Uranus.
  • March 7: One hour after sunset, brilliant Venus is over one-third of the way up in the west. It is 2.3° to the right of Uranus. 
  • March 8: Daylight Saving Time begins today.  One hour after sunset, Venus (m = −4.4) over 30° up in the west, is 2.2° to the upper right of Uranus and 5.4° to the lower left of Gamma Arietis (γ Ari, m = 3.9). 
  • March 9: One hour after sunset, Venus is 32° in altitude, 2.6° to the upper right of Uranus. Brilliant Venus passes 6.7° to the lower left of Beta Arietis (β Ari, m = 2.6).
  • March 10: In the evening, one hour after sunset, brilliant Venus is over 32° up in the west and 3.3° to the upper right of Uranus. Through a telescope, Venus is 58% illuminated and 20” across. Three hours after sunset (about 10 p.m. CDT), the moon (16.5d, 97%) is nearly 16° up in the east-southeast. It is 2.2° to the lower left of Gamma Virginis (γ Vir, m = 3.4).
  • March 11: In the evening – one hour after sunset – brilliant Venus is over 32° up in the west, 4.1° to the upper right of Uranus and near the three bright stars of Aries. 


2020, March 28: Spectacular Grouping of Venus, Crescent Moon, and Pleiades

March 28, 2020: Venus, the crescent moon, and the Pleiades Cluster are near each other.

Venus appears near the moon and the Pleiades star cluster on the evening of March 28, 2020. 

Start looking for Venus and the moon about an hour after sunset.  As the sky darkens further, the Pleiades star cluster is fully revealed.  The trio makes a pretty triangle.  By the end of evening twilight, about 90 minutes after sunset, the sky is fully dark naturally and the grouping sparkles in the western sky.

The crescent moon is only 18% illuminated.  It is only 4.7 days past its New phase.

The star Aldebaran, the brightest in Taurus, appears to the upper left of the grouping.

Use tripod-camera to capture the triple grouping.  Exposures from 1-10 seconds will capture earthshine on the moon.  Reflected sunlight from Earth gently illuminates the night portion of the moon.

Link to Venus during March 2020 article.

2020, March 31: Saturn – Mars Conjunction


Mars passes Saturn, March 31, 2020

On March 31, Mars passes Saturn.  The trio of planets – Jupiter, Saturn, and Mars – span 6.1°.  This is the closest the three planets have appeared in the sky since April 14, 2000.

This morning is the Saturn – Mars conjunction! One hour before sunrise, Mars, 16° up in the southeast is 0.9° to the lower right of Saturn. Bright Jupiter is to the upper right of Saturn and Mars.

The Mars – Saturn gap grows after the conjunction: Apr 1, 1°; Apr 2, 1.4°; Apr 3, 1.9°; Apr 4, 2.5°; Apr 5, 3.1°; Apr 6, 3.7°; Apr 7, 4.3°; Apr 8, 5.0°.

Link to summary of March 2020 planetary activity.