Robert W Williams
@robertwwilliams.bsky.social
Paleontologist / palynologist. Dinoflagellate taxonomy through 220 million years of evolution, which coincidentally is the time span of one Milky Way rotation.
Astrophotographer and telescope optics maker.
https://www.dinium.net/english/
Astrophotographer and telescope optics maker.
https://www.dinium.net/english/
Yes, you are correct. I think they are shadows of tall spruce on a hill 700 m behind our house, precisely where the sun set that October day.
December 8, 2025 at 3:07 PM
Yes, you are correct. I think they are shadows of tall spruce on a hill 700 m behind our house, precisely where the sun set that October day.
Often overlooked, but very beautiful. When the sky is clear, one can see the Earth's shadow rise in the east as the sun sets in the west. Looking eastward towards the mainland, here we see the shadow of the North Sea rising over the Ryfylke mountains of Norway. ðŸ”
December 8, 2025 at 10:51 AM
Often overlooked, but very beautiful. When the sky is clear, one can see the Earth's shadow rise in the east as the sun sets in the west. Looking eastward towards the mainland, here we see the shadow of the North Sea rising over the Ryfylke mountains of Norway. ðŸ”
Stunning discovery! The Vera C. Rubin Observatory arrives in the nick of time to help sort this out.
November 12, 2025 at 6:32 PM
Stunning discovery! The Vera C. Rubin Observatory arrives in the nick of time to help sort this out.
That would have been a winner photo. Here at 59°N in southwest Norway, the night sky has been overcast and rainy for nine weeks, minus 2 or 3 nights of intermittent non-cloudiness. Frustrating.
November 12, 2025 at 10:59 AM
That would have been a winner photo. Here at 59°N in southwest Norway, the night sky has been overcast and rainy for nine weeks, minus 2 or 3 nights of intermittent non-cloudiness. Frustrating.
Yeah, it's a lot of work. More than a regular solid glass disk. One must not exert much pressure on this kind of glass.
November 11, 2025 at 9:18 PM
Yeah, it's a lot of work. More than a regular solid glass disk. One must not exert much pressure on this kind of glass.
Reposted by Robert W Williams
Oh well, it's only takes years of trial and error studying various techniques and inhuman quantities of patience. Here's 2000 hours compressed to 30 seconds. 24 inch (62 cm) diameter f/3.4 paraboloid primary mirror.
November 11, 2025 at 12:58 PM
Oh well, it's only takes years of trial and error studying various techniques and inhuman quantities of patience. Here's 2000 hours compressed to 30 seconds. 24 inch (62 cm) diameter f/3.4 paraboloid primary mirror.
Oh well, it's only takes years of trial and error studying various techniques and inhuman quantities of patience. Here's 2000 hours compressed to 30 seconds. 24 inch (62 cm) diameter f/3.4 paraboloid primary mirror.
November 11, 2025 at 12:58 PM
Oh well, it's only takes years of trial and error studying various techniques and inhuman quantities of patience. Here's 2000 hours compressed to 30 seconds. 24 inch (62 cm) diameter f/3.4 paraboloid primary mirror.
Reposted by Robert W Williams
Precisely! These satellites are simply pinhole cameras producing an image of the sun, which at 600 km distance is 5 km in diameter. A "giant" 18-meter reflector is an imaging optic of focal ratio f/33333. That's not solar power boosting. It's a brighter than usual Iridium flash!
November 8, 2025 at 3:57 AM
Precisely! These satellites are simply pinhole cameras producing an image of the sun, which at 600 km distance is 5 km in diameter. A "giant" 18-meter reflector is an imaging optic of focal ratio f/33333. That's not solar power boosting. It's a brighter than usual Iridium flash!
Precisely! These satellites are simply pinhole cameras producing an image of the sun, which at 600 km distance is 5 km in diameter. A "giant" 18-meter reflector is an imaging optic of focal ratio f/33333. That's not solar power boosting. It's a brighter than usual Iridium flash!
November 8, 2025 at 3:57 AM
Precisely! These satellites are simply pinhole cameras producing an image of the sun, which at 600 km distance is 5 km in diameter. A "giant" 18-meter reflector is an imaging optic of focal ratio f/33333. That's not solar power boosting. It's a brighter than usual Iridium flash!
Thanks for the info. So it can be a rubble pile. I didn't know they could be so tightly packed!
September 19, 2025 at 5:17 PM
Thanks for the info. So it can be a rubble pile. I didn't know they could be so tightly packed!
Reposted by Robert W Williams
Assuming a rubble pile with a density of 1800 kg/cubic metre, the gravitational acceleration on its surface is 2,77e-6 metres per second squared. Spinning once in five minutes, the centrifugal acceleration is 870 times more than gravity. It couldn't exist as a rubble pile. Seems to be a solid body.
September 19, 2025 at 11:06 AM
Assuming a rubble pile with a density of 1800 kg/cubic metre, the gravitational acceleration on its surface is 2,77e-6 metres per second squared. Spinning once in five minutes, the centrifugal acceleration is 870 times more than gravity. It couldn't exist as a rubble pile. Seems to be a solid body.
Assuming a rubble pile with a density of 1800 kg/cubic metre, the gravitational acceleration on its surface is 2,77e-6 metres per second squared. Spinning once in five minutes, the centrifugal acceleration is 870 times more than gravity. It couldn't exist as a rubble pile. Seems to be a solid body.
September 19, 2025 at 11:06 AM
Assuming a rubble pile with a density of 1800 kg/cubic metre, the gravitational acceleration on its surface is 2,77e-6 metres per second squared. Spinning once in five minutes, the centrifugal acceleration is 870 times more than gravity. It couldn't exist as a rubble pile. Seems to be a solid body.
Yes! In addition to moons in movies and TV, ever since the Renaissance, nocturnes have rarely shown a gibbous moon, favoring a crescent or full moon instead.
September 7, 2025 at 9:25 AM
Yes! In addition to moons in movies and TV, ever since the Renaissance, nocturnes have rarely shown a gibbous moon, favoring a crescent or full moon instead.
#15 MoviesToGetToKnowMe
2001: A Space Odyssey
2001: A Space Odyssey
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2001: A Space Odyssey
2001: A Space Odyss...
2001...
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2001...
Arrival
2001: A Space Odyssey
2001: A Space Odyssey
2001: A Space Odyssey
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2001: A Space Odyssey
2001: A Space Odyssey
2001: A Space Odyssey
2001: A Space Odyssey
2001: A Space Odyssey
2001: A Space Odyss...
2001...
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2001...
Arrival
August 17, 2025 at 7:32 AM
#15 MoviesToGetToKnowMe
2001: A Space Odyssey
2001: A Space Odyssey
2001: A Space Odyssey
2001: A Space Odyssey
2001: A Space Odyssey
2001: A Space Odyssey
2001: A Space Odyssey
2001: A Space Odyssey
2001: A Space Odyssey
2001: A Space Odyssey
2001: A Space Odyss...
2001...
2001...
2001...
Arrival
2001: A Space Odyssey
2001: A Space Odyssey
2001: A Space Odyssey
2001: A Space Odyssey
2001: A Space Odyssey
2001: A Space Odyssey
2001: A Space Odyssey
2001: A Space Odyssey
2001: A Space Odyssey
2001: A Space Odyssey
2001: A Space Odyss...
2001...
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Arrival
Yes, thats why all the giant observatories are at low attitudes. Most are between apprx 28 deg north (Hawaii & Canary Islands)) and south (Chile & South Africa). One can see both the northern and southern skies. Ah yes, a mobile phone + eyepiece will do the Moon, Venus, Mars, Jupiter and Saturn.
August 3, 2025 at 6:06 PM
Yes, thats why all the giant observatories are at low attitudes. Most are between apprx 28 deg north (Hawaii & Canary Islands)) and south (Chile & South Africa). One can see both the northern and southern skies. Ah yes, a mobile phone + eyepiece will do the Moon, Venus, Mars, Jupiter and Saturn.
Thanks. The northern hemisphere offers enough nebulae, galaxies and star clusters to keep one busy for a lifetime. The beauty of the southern hemisphere is that the core of the Milky Way passes overhead, instead of only appearing low on the southern horizon. The core is truly sublime. Breathtaking.
August 3, 2025 at 5:07 PM
Thanks. The northern hemisphere offers enough nebulae, galaxies and star clusters to keep one busy for a lifetime. The beauty of the southern hemisphere is that the core of the Milky Way passes overhead, instead of only appearing low on the southern horizon. The core is truly sublime. Breathtaking.
🤣It would seem so! However, mainland Norway's latitude (58-71 N) is not optimal for optical astronomy. No total darkness from April to September, and winter skies are often overcast. North of 65 degrees, the aurora is a problem. What's more, the beautiful southern sky is always below the ground.😞
August 3, 2025 at 2:15 PM
🤣It would seem so! However, mainland Norway's latitude (58-71 N) is not optimal for optical astronomy. No total darkness from April to September, and winter skies are often overcast. North of 65 degrees, the aurora is a problem. What's more, the beautiful southern sky is always below the ground.😞
Thanks so much! 🙂
August 3, 2025 at 8:51 AM
Thanks so much! 🙂
Yes, I built the machine myself. It is based on the "fixed-post" or "spindle grinder/polisher" concept. My goal was twofold: Make it 1) much more stable than necessary, and 2) pleasing to the eye. The former is always a good idea in optics and the latter is simply because it's possible! 🙂
August 3, 2025 at 8:49 AM
Yes, I built the machine myself. It is based on the "fixed-post" or "spindle grinder/polisher" concept. My goal was twofold: Make it 1) much more stable than necessary, and 2) pleasing to the eye. The former is always a good idea in optics and the latter is simply because it's possible! 🙂
Thanks. I hope to finish it by the end of September. Then it's off to Hamburg for aluminizing.
August 2, 2025 at 11:14 PM
Thanks. I hope to finish it by the end of September. Then it's off to Hamburg for aluminizing.
Many thanks.🙂
August 2, 2025 at 10:22 PM
Many thanks.🙂
Since I recently retired, I can gleefully work all day figuring and testing my 62 cm (24 inch) cellular primary mirror. Having produced a good spheroidal figure, it's finally ready to parabolize. Amazingly, this is Norway's largest optical telescope. ðŸ”
August 2, 2025 at 6:34 PM
Since I recently retired, I can gleefully work all day figuring and testing my 62 cm (24 inch) cellular primary mirror. Having produced a good spheroidal figure, it's finally ready to parabolize. Amazingly, this is Norway's largest optical telescope. ðŸ”
I feel your enthusiasm; that would induce squee! However, my inner pedant says that to subtend 1/2 a degree when held at arm's length, the disk must have a diameter of half the width of our little finger.
May 26, 2025 at 6:10 AM
I feel your enthusiasm; that would induce squee! However, my inner pedant says that to subtend 1/2 a degree when held at arm's length, the disk must have a diameter of half the width of our little finger.
Elegant idea! A quick, qualitative documentation of seeing at a particular time and altitude above the horizon.
February 10, 2025 at 11:24 PM
Elegant idea! A quick, qualitative documentation of seeing at a particular time and altitude above the horizon.
It is. Yes it is.
January 28, 2025 at 9:10 PM
It is. Yes it is.