Posts by AlphaCephei@mastodontech.de
(DIR) Post #AUeFgjZpwUXUAYmU4m by AlphaCephei@mastodontech.de
2023-04-14T16:29:08Z
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@zdfheute Und das ist gut so!https://www.ardalpha.de/wissen/umwelt/nachhaltigkeit/lichtverschmutzung-lichtsmog-nacht-himmel-licht-sterne-tiere-insekten-100.html
(DIR) Post #AXUocniV5whgo9y7d2 by AlphaCephei@mastodontech.de
2023-07-08T20:50:22Z
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@Revertron Absolutely right. The big bang happened everywhere at the same time and space has been expanding ever since. The speed of expansion depends on the distance. Some galaxies are so far away that space grows faster than light between us and them. Light needs to travel through the expanding space to reach us - like an ant crawling between 2 points on a balloon while it is inflated. That's why it takes so long to reach us although the galaxies were 10-20x closer when they emitted that light
(DIR) Post #AXUpKDwlRpeWbxLWbY by AlphaCephei@mastodontech.de
2023-07-08T20:55:16Z
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@Revertron Where these galaxies are: all around us. When we look into the distance, we look into the past. Space expands with equal speed in all directions, so equal distance means equal lookback time. The big bang happened everywhere, so you would see it all around you, if you could - but we can only "see" (with radio telescopes) up to the cosmic microwave background, basically the fireball of the big bang that became eventually transparent so light could travel in straight lines afterwards.
(DIR) Post #AYQxy3V84i92D3DYYK by AlphaCephei@mastodontech.de
2023-08-05T22:08:22Z
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@Revertron But that IS exactly the standard explanation of #darkenergy , that it is an inherent property of space. Without Dark Energy, the expanding matter would pull space with it and slow down the expansion, with or without an eventual stop and rebound. But Dark Energy gives an extra push that overwhelms the mutual attraction of galaxies and makes them speed up. There is just no quantifiable explanation as to what effect causes this push. Vacuum energy is a candidate but 10^120 too strong...
(DIR) Post #AYR647eIMjBoRcuPUO by AlphaCephei@mastodontech.de
2023-08-05T23:39:12Z
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@Revertron Actually, it is an expansion of space, no actual pushing via F=m*a. Objects stay in place, but more space is created between them. Like a cake with raisins expanding while being baked. An object could actually slip over the expansion of space away from another object by just moving at the same speed that space grows between them in the opposite direction. Other forces and the required fine balancing neglected, it would keep the same distance forever with no propulsion required.
(DIR) Post #AZCf4TSyaApm4kkbKa by AlphaCephei@mastodontech.de
2023-08-28T22:22:32Z
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@ZDF Was sind nochmal Disketten?
(DIR) Post #AZEfWnK4jrkk5G0lgu by AlphaCephei@mastodontech.de
2023-08-29T21:23:59Z
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@ankedb@linksfraktion.de Kam meines Wissens nach ursprünglich aus einer Meldung einer niederländischen Zeitung, die eine Äußerung der Sprecherin der Küstenwache (dass sich an Bord Elektroautos befänden, die schwerer zu löschen seien) falsch wiedergab (dass das Feuer vermutlich an einem E-Auto begann). Reuters verbreitete sie dann weiter. Nicht nur die Bild, auch NDR und ARD behaupteten danach, dass das Feuer durch ein brennendes Elektroauto ausgelöst worden sei.
(DIR) Post #Aa2JrKy48WoDjJ6Dbs by AlphaCephei@mastodontech.de
2023-09-22T20:29:53Z
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@deutschlandfunk Ausgerechnet die Fußgänger zu blockieren ist wieder mal so eine Schnapsidee. Ich bin ja eigentlich für deren Einsatz und verteidige sie meistens, es soll ja auch weh tun (die Klimakatastrophe tut noch viel mehr weh) aber solche Mittel entweihen den Zweck.
(DIR) Post #AaoBjnnRTD7T3qWspk by AlphaCephei@mastodontech.de
2023-10-15T22:45:27Z
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@freemo Not entirely true. You are confusing (overall) brightness with surface brightness. Surface brightness, that is light power received per unit solid angle, does not decrease with distance, but since luminous area decreases with distance squared, so does overall brightness = solid angle * surface brightness. For this reason, photographing the Moon (same distance from Sun as Earth) requires the same exposure settings as a sunlit landscape, but Saturn (10x distance) 100x more (+6.6 EV)
(DIR) Post #AaoC4oitDihK13Q98i by AlphaCephei@mastodontech.de
2023-10-15T22:48:00Z
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@freemo Also, on the surface of the Sun, the area from with light reaches you, is 180°x180°, way more than the 0.5x0.5° as seen from Earth. So you will be toast within a fraction of a second, although a 0.5x0.5° piece of the Sun would be the same brightness as seen from Earth.
(DIR) Post #AaoCS1N0MhDjttFUJM by AlphaCephei@mastodontech.de
2023-10-15T22:53:27Z
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@freemo Well, you will certainly be toast very quickly, but you didn't define what "brightness" means, so the post was not unambiguous. To a layman, brightness usually means how bright something is lit by the light source (at a particular distance, that is). Surface brightness is a concept that needs to be introduced.
(DIR) Post #AaoCz2RNPE0cmE2Nou by AlphaCephei@mastodontech.de
2023-10-15T22:59:24Z
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@freemo Perceived brightness of a *particular viewing angle smaller than the viewing angle of the object*. The object in whole expanse, as long as it fits the field of view, does in fact get brighter when it is closer, because the viewing angle increases. And therefore, it lights up closer objects (say, Mercury) more than objects farther away (e,g. Saturn)
(DIR) Post #AaoDEjNo1sICIuqlqC by AlphaCephei@mastodontech.de
2023-10-15T23:02:16Z
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@freemo True, the heat production of a particular volume of the solar core has been likened to that of a dunghill of the same volume. The Sun is very ineffective at fusing hydrogen, that's why it last so long. But it is also a very big dunghill, so to say...😁
(DIR) Post #AaoE1sAi8pI9kf9pxY by AlphaCephei@mastodontech.de
2023-10-15T23:11:08Z
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@freemo That's surface brightness again. Each retina cell receives the same amount of light, but more cells receive light, so the *object* gets brighter *overall*. The projection of the Sun inside the eye is something else again than the illumination of a piece of surface like a planet.I know all that, I know that a telescope will not make the Andromeda galaxy appear brighter per unit area as naked eye but it will increase contrast to the background & large objects are easier to see than small.
(DIR) Post #AaoENPOhnuigseyMcK by AlphaCephei@mastodontech.de
2023-10-15T23:13:06Z
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@freemo I'm dropping out here, it's 1:12 am, need to go to bed now. Have a good night and clear skies!🌌
(DIR) Post #Aap0e7aG5FKsM5PZ8y by AlphaCephei@mastodontech.de
2023-10-16T08:15:53Z
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@freemo Nope. This only holds for point sources. Ojects get brighter in telescopes the less magnification is used (more light in less area). However, the *exit pupil* of the telescope also gets larger as mag. decreases. Exit pupil > eye pupil wastes light outside the eye pupil. The optimal mag. (Mo) for aperture D is at exit pupil=eye pupil Ø (≈7mm). Exit pupil = D/M, so Mo = D/7mm. A gains (D/7mm)^2 more light but extends object area by Mo^2=(D/7mm)^2 which cancels. Seehttps://www.rocketmime.com/astronomy/Telescope/SurfaceBrightness.html
(DIR) Post #Aapb8rvJQ6Ogi12MZk by AlphaCephei@mastodontech.de
2023-10-16T08:16:54Z
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@freemo Therefore, D=N*7mm yields same surface brightness as D=7mm, only at Nx magnification. This is the reason why there are 7x50 glasses but no 6x50. It's basically the same principle as in your initial post: telescopes make things appear closer. That's why I thought we are on the same line here. It's different for photography where exposure time depends on f-stop number (focal length/D), or point sources where all light ends up in 1 retina cell. I know telescopes for ~50 years, I have 3.
(DIR) Post #Aapb8tsCAf5mkvatzk by AlphaCephei@mastodontech.de
2023-10-16T08:20:00Z
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@freemo I have even studied astronomy for a couple of semesters. I would have become an astronomer if computer science which I also loved wouldn't have been more promising financially. But I'm still an amateur astronomer and write articles on astronomical topics. I know what I'm talking about.
(DIR) Post #Aaq32PSx6n5dQeTqu8 by AlphaCephei@mastodontech.de
2023-10-16T20:17:23Z
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@freemo Correct, as the surface brightness is constant. Which is what the light meter measures. You could also take the Moon as the bonfire. 1/250 s at f/16 and ISO 100 will give you a nicely exposed image. You could use the same setting on Earth (in sunshine) - or on the surface of the Moon.However, the *overall* brightness of the Moon as seen fro Earth is barely enough to read a newspaper headline, while on the Moon, you could easily read the newspaper in reflected Moonlight.