Can shadows on a sundial go clockwise or counterclockwise, depending on the time of day? In the northern hemisphere, the sun is below a building casting a shadow, so when the earth rotates "east", the shadow starts at around 9 AM and finishes around 3 pm. Shadow went clockwise.
-
Show this thread
-
In the southern hemisphere, the sun is above a building casting a shadow. If you're observing this from the sun, the earth rotates to the right. The shadow starts at around 9 AM and finishes around 3 pm. Shadow went counterclockwise.
1 reply 0 retweets 0 likesShow this thread -
It turns out that, if you are near the equator, at certain times of the year, because of the tilt on the earth's axis, you seasonally (i.e. winter/summer) can go from counterclockwise shadows to clockwise shadows and vice versa.
1 reply 0 retweets 0 likesShow this thread -
So, for example, if you're in Caracas, Venezuela (north of the equator). For most of the year your shadows go clock wise, but during the peak of summer the earth tilts you down below the median of the sphere and you end up "below the sun" giving you counterclockwise shadows.
1 reply 0 retweets 0 likesShow this thread -
This app shows this pretty well: http://andrewmarsh.com/apps/staging/sunpath3d.html … So that's pretty cool. A fun visualization exercise.pic.twitter.com/30B3vHpq7f
1 reply 0 retweets 0 likesShow this thread -
Molson Hart Retweeted Patrick Collison
But here is what I do not understand. I don't see how this could be true without: 1. It being an illusion 2. The earth pulling a DJ scratch (going east then west then back east) 3. The sun popping up and down What am I missing/not understanding here?https://twitter.com/patrickc/status/1138615790012370944 …
Molson Hart added,
Patrick CollisonVerified account @patrickcWas very confused by the shadows on the ground in Singapore yesterday until I realized that, below 23.50 of latitude, shadows in the northern hemisphere can (in the summer) move both clockwise *and* counterclockwise, depending on the time of day.
(See http://andrewmarsh.com/apps/staging/sunpath3d.html ….)1 reply 0 retweets 0 likesShow this thread -
Molson Hart Retweeted Luis Batalha 🇵🇹 🇺🇸
This was cited as the reason for this occurring, but I can't find any evidence that the sun goes into retrograde (or the earth goes into retrograde from the vantage point of the sun). So basically I don't get it.https://twitter.com/luismbat/status/1138624307217588224 …
Molson Hart added,
Luis Batalha 🇵🇹 🇺🇸 @luismbatReplying to @patrickcThis was predicted by the Portuguese mathematician Pedro Nunes in 1537 at the time of the portuguese discoveries. It was also the first natural phenomenon to be predicted by math before being observed :) https://thatsmaths.com/2017/10/12/pedro-nunes-and-solar-retrogression/ …1 reply 0 retweets 0 likesShow this thread -
Technically, every day a year, every city close enough to the equator to experience a seasonal change in shadow direction, will have its shadows switch direction, but it would basically be unobservable because on that day the sun's position would mean shadows wouldn't rotate.
1 reply 0 retweets 0 likesShow this thread
Planets go retrograde because we're on the earth, which is not in direct orbit with the planet that we are observing, unlike the sun and moon.pic.twitter.com/VCM4Ag5wZ3
Loading seems to be taking a while.
Twitter may be over capacity or experiencing a momentary hiccup. Try again or visit Twitter Status for more information.