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Old 2021-10-31, 21:47   #23
a1call
 
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When it comes to atmospheric glare obscuring stars there are conflicting mainstream posits. Though not exactly the same as stars obstruction on Moon, it is perhaps related. There are those authoritative claims that you can absolutely not see stars from a bottom of a dark well during the day and there are plenty of 1st hand claims to the contrary:

Google Search
Quote:
you can see stars from the bottom of a well even in daylight.

Can you see stars in daytime, by looking up from the bottom of a well or a tall chimney? Surprisingly, you can actually see a few stars or planets in daytime, but unfortunately, looking through a long tube actually makes it harder.
A google Search a Decade ago would return results completely ruling it out.

ETA AFAIK, There are no claims that anyone has seen any stars during the daytime by looking through black pipes/tubes. There are claims that some can see stars in the daytime without any aids and by training. I also seem to recall that there are high powered telescopes that can see some stars in the daytime.

Last fiddled with by a1call on 2021-10-31 at 21:58
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Old 2021-10-31, 21:51   #24
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Quote:
Originally Posted by Dobri View Post
Earth's equatorial circumference = 40,075.017 km, (40,075.017 × 7.2)/360 = 801.5 km, which is the estimated distance between Aswan (Syene) and Alexandria (the actual distance is 843 km), and
Moon's equatorial circumference = 10,921 km km, (10,921 × 30)/360 = 910 km, so the distances are comparable indeed.
However, they would have difficulties when travelling along a straight line and measuring distances if there is no simple notion about North, South, East and West.
A single rotation of the Moon around its axis takes approximately four weeks and the stars would be spinning slowly during the night (lasting for two weeks) making it harder to select an equivalent of a Polar star.
There is no magnetic field to use a compass.
Unless they invent a long lasting gyroscope, their development would be greatly delayed as compared to our ancestors.
Ancient Chinese to the recue:

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The south-pointing chariot (or carriage) was an ancient Chinese two-wheeled vehicle that carried a movable pointer to indicate the south, no matter how the chariot turned. Usually, the pointer took the form of a doll or figure with an outstretched arm. The chariot was supposedly used as a compass for navigation and may also have had other purposes.
.....

The south-pointing chariot, a mechanical-geared, wheeled vehicle used to discern the southern cardinal direction (without magnetics), was given a brief description by Ma's contemporary Fu Xuan.[3] The contemporary 3rd century source of the Weilüe, written by the East Han Dynasty politician Yuan Huan also described the south-pointing chariot of belonging to the Chinese mechanical engineer and politician Ma Jun.[4] The Jin Dynasty (266–420) era text of the Shu Zheng Ji (Records of Military Expeditions), written by Guo Yuansheng, recorded that south-pointing chariots were often stored in the northern gatehouse of the Government Workshops (Shang Fang) of the capital city.[4] However, the later written Song Shu (Book of Song) (6th century) recorded the south-pointing chariot's design and use in further detail, as well as creating the background legend of the device's (supposed) use long before Ma's time, in the Western Zhou Dynasty (1050–771 BC). The book also provided a description of the south-pointing chariot's re-invention and use in times after Ma Jun and the Three Kingdoms. The 6th century text, translated by the British scientist and historian Joseph Needham, reads as follows (the south-pointing chariot is referred to as the south-pointing carriage):

.........
https://en.wikipedia.org/wiki/South-pointing_chariot
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Old 2021-10-31, 21:59   #25
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Quote:
Originally Posted by a1call View Post
When it comes to atmospheric glare obscuring stars there are conflicting mainstream posits. Though not exactly the same as stars obstruction on Moon, it is perhaps related. There are those authoritative claims that you can absolutely not see stars from a bottom of a dark well during the day and there are plenty of 1st hand claims to the contrary:

Google Search


A google Search a Decade ago would return results completely ruling it out.
But the moon has no atmosphere and the only glare you have to contend is the reflection of the landscape. it is not the lansdscape's reflection that prevents you from seeing stars during daytime as much as general luminosity of the atmosphere.
Being able to observe Venus 95% of the time would be very helpful .

Last fiddled with by rudy235 on 2021-10-31 at 22:10 Reason: Clarifying
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Old 2021-10-31, 22:01   #26
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Please see my ETA for post number 23.
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Old 2021-10-31, 22:26   #27
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On the Moon, without a significant atmosphere, I think you wouldn't need a tube, just a flat opaque light block of some sort below your field of view would be enough. Wait for your iris to adjust and now you can see the stars.

Perhaps some type of neck ring, like the ruff of old, would be sufficient. As long as your view of the surrounding landscape was completely blocked then there isn't any other stray light to obscure your view.
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Old 2021-11-01, 00:16   #28
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Found this from my old hangout:

Quote:
On the way there, they had been in sunlight so it was harder to see the stars. Neil's statements were made when they were in lunar shadow. From here:
https://forum.cosmoquest.org/showthr...59#post1885159



Quote:
071:59:20 Armstrong: Houston, it's been a real change for us. Now we're able to see stars again and recognize constellations for the first time on the trip. It's - the sky is full of stars. Just like the night side of Earth. But all the way here, we've only been able to see stars occasionally and perhaps through the monocular, but not recognize any star patterns.
071:59:52 McCandless: I guess it's turned into night up there really, hasn't it?
071:59:58 Armstrong: Really has.
https://history.nasa.gov/afj/ap11fj/...-approach.html

Last fiddled with by a1call on 2021-11-01 at 00:17
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Old 2021-11-01, 12:00   #29
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Quote:
Originally Posted by rudy235 View Post
Wouldn't a 1 meter long metal or wooden tube of 4 centimeter diameter (40 inches x 11/2 inches ø) be enough to avoid the glare? (Even better if it were in a binocular version.)
Presumably, if you could arrange no leakage around the eyes.

OTOH, astronomical equipment with sub-arcminute naked eye precision tends to be rather large and a pit would be only a small fraction of the cost and size of the observatory. Take Uraniborg as a terrestrial example.
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Old 2021-11-01, 12:07   #30
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Quote:
Originally Posted by Dobri View Post
Earth's equatorial circumference = 40,075.017 km, (40,075.017 × 7.2)/360 = 801.5 km, which is the estimated distance between Aswan (Syene) and Alexandria (the actual distance is 843 km), and
Moon's equatorial circumference = 10,921 km km, (10,921 × 30)/360 = 910 km, so the distances are comparable indeed.
However, they would have difficulties when travelling along a straight line and measuring distances if there is no simple notion about North, South, East and West.
A single rotation of the Moon around its axis takes approximately four weeks and the stars would be spinning slowly during the night (lasting for two weeks) making it harder to select an equivalent of a Polar star.
There is no magnetic field to use a compass.
Unless they invent a long lasting gyroscope, their development would be greatly delayed as compared to our ancestors.
There would be absolutely no problem determining the north-south axis or distances to precision attained by people 2000 years ago.

Us a plumb line to erect a vertical pole. Measure the length between the base of the pole and the tip of the shadow throughout the day. When it is shortest you have your axis. Euclidean geometry now tells you your latitude. As for geodesy, how do you think the old imperial length measuments of rods, links and chains got their names?

Amusing sideline: when I fixed an equatorial head to an old tree stump I used exactly the pole and shadow technique to find which direction was north. I couldn't see Polaris from that position in the garden.

Anyway, 2000 years ago Polaris wasn't a particular accurate way of determining either northwards or latitude. Ever heard of precession?

Last fiddled with by xilman on 2021-11-01 at 12:10
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Old 2021-11-01, 12:18   #31
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Quote:
Originally Posted by Dobri View Post
Earth's equatorial circumference = 40,075.017 km, (40,075.017 × 7.2)/360 = 801.5 km, which is the estimated distance between Aswan (Syene) and Alexandria (the actual distance is 843 km), and
Moon's equatorial circumference = 10,921 km km, (10,921 × 30)/360 = 910 km, so the distances are comparable indeed.
It's not the distances that are so important as the angles.

If the angles can be measured at least as accurately as on Earth, a 7.2 degree change in latitude will give the same measurement of shadows. The overland distance to be measured is then (40/11) = 3.6 times shorter, or 230km, and so even easier to measure than on the Earth.
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Old 2021-11-01, 13:10   #32
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Quote:
Originally Posted by xilman View Post
Us a plumb line to erect a vertical pole. Measure the length between the base of the pole and the tip of the shadow throughout the day. When it is shortest you have your axis. Euclidean geometry now tells you your latitude. As for geodesy, how do you think the old imperial length measuments of rods, links and chains got their names?
The only issue with this human approach is that on the Moon the Sun shines for two weeks during the lunar day so one has to wait quite some time to observe the shortest tip of the shadow.
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Old 2021-11-01, 13:21   #33
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Quote:
Originally Posted by xilman View Post
It's not the distances that are so important as the angles.

If the angles can be measured at least as accurately as on Earth, a 7.2 degree change in latitude will give the same measurement of shadows. The overland distance to be measured is then (40/11) = 3.6 times shorter, or 230km, and so even easier to measure than on the Earth.
Anyway, the travel restriction could make them think that they are living on some kind of a curved surface, not necessarily a sphere.
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