Urban Astronomy – Conjunction in December

Posted December 2, 2020

The night sky is pretty much a mystery to most City Dwellers.  The glare of city light drowns out all but the brightest stars – and planets don’t do much better.  If you are interested, I can tell you where to look to see these far-off worlds.  If you were not interested, you would have stopped reading after the first sentence.  So, at this point, I know my audience. 

Urban Astronomy

Background: Occultations

Jupiter and Saturn were already close together in November.  Now they are bound for near-occultation in December.  An occultation is when one astronomical body passes in front of another.  It happens quite frequently with the moon passing in front of stars and sometimes planets.  Occasionally planets and asteroids do so.  Long ago, before space telescopes and sophisticated image processing, these occultations were used to characterize the shape and size of asteroids by distributing observers across the planet to time the disappearance and reappearance of stars as the asteroid passed in front of same.  To understand this, imagine the shadow cast by asteroid across the face of the Earth.  The durations observed by various locations measures the shadow precisely.  This was done in the case of near-Earth asteroid Eros and its shape was determined to be something like a fat cigar.

Much later, Eros was visited by a space probe called NEAR (Near Earth Asteroid Rendevous).  You see below that the shape was confirmed.

Near Earth Asteroid Eros: (remember, I said “something like…”)


I told you all that because it is interesting.  But that won’t happen with Jupiter and Saturn.  Rather, they will be so close in the sky that it will take near-perfect vision to see them as two objects.  Once again, I will use the moon as a sort of cursor to point out this event.

On December 16, 2020 at 6PM (this is Central Standard Time in Houston) you will see – low in the Southwestern sky –  a thin crescent moon near the pair of planets that will appear only a fraction of a degree apart.  Please remember that your thumb at arm’s length covers about one degree of sky.


An image of what you will see from The December 2020 Great Conjunction  By Graham Jones, appears below. 

A sky map – from Heavens-Above.com –  like those I’ve shown before, appears below:


Keep watching over the following week – you will not have the moon as a landmark, so, remember where Jupiter and Saturn were on the 16th and look there again. On December 21, the two will be about one tenth of a degree apart.  This close an approach of the two planets last happened on July 16, 1623.

Hasta Luego,


Artist’s conception:   https://www.timeanddate.com/astronomy/planets/great-conjunction

Heavens-Above (Houston):   https://heavens-above.com/main.aspx?lat=29.7382&lng=-95.6329&loc=13811&alt=0&tz=CST

Heavens Above (Oslo):     https://heavens-above.com/main.aspx?lat=59.9133&lng=10.739&loc=Oslo&alt=0&tz=CET

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