Monday, December 21, 2020

checked the split limit

I've been seeing and hearing about an aspect of the conjunction of Jupiter and Saturn that doesn't sound right. Purportedly, people are saying the two planets will merge to form one point of light. I don't think so.

Let's do a comparison. 

Mizar and Alcor are separated by about 12 minutes of arc (').

Mizar and Alcor at 12 arc-minutes separation

Jupiter and Saturn today at 6:37 PM Universal Coordinated Time will be about 6 arc-minutes apart.

Jupiter and Saturn 6 arc-minutes apart

The Moon, as previously discussed, is around 30 minutes.

From Observing and Measuring Visual Double Stars by R.W. Argyle (second edition), it is stated:

A normal pair of eyes should be able to see... 5.5 minutes without difficult and some may be able to make out... 3.6'.

This matches up with a very old note that I had.

The closest separation the eye can distinguish about 4 minutes of arc.

So, to conclude, people with good vision will be able to "split" the two planets. In other words, they will not merge.

A new vision test...


Updated from Dr Ralph Chou.

The "normal" minimum angle of resolution of the eye is 1 arc-minute - that is what is referred to as 20/20 vision.  Many young adults have 20/15 vision, a MAR of 0.75 arc-min.  [That] is for daylight-adapted (photopic) vision.  With dark adaptation, rod vision comes to the fore, and the MAR will become larger.  A limit of 4 arc-min seems reasonable for mixed rod and cone vision in mesopic conditions that are more typical of a city nightscape.

There you have it with 4' being reasonable.

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