lurker2718 @ lurker2718 @lemmings.world

Posts

0

Comments

41

Joined

2 yr. ago

I just want to say, i loved Dragon's Egg for this level of detail to the physics. I even did some quick calculations why you want 6 compensator masses not less to reduce the effect of tidal forces. Or the black holes inside the sun, at first i thougt, this is impossible. Then i read some more on it an noticed its well researched.

The links are actually only random images from an image search with the terms "solar eclipse through tree leaves" and "iss in front of sun".

I think you have in mind, that the rays are not parallel because they have to arrive at different positions. As you say, this is negligible, and it can even be avoided by the tilting of the mirrors. However, the rays start from different parts of the sun, and as the sun is huge, this angle is not so small.

I'll try to explain it in more detail, sorry for the wall of text, it got longer than expected. In this case, we can use simplified ray optics and ignore the wave nature of light. This means, the light of the different mirrors or even pieces of mirrors just adds to one another. An important point, even if obvious, is that each point on the mirror surface can only have one orientation. Now we "select" the orientation of this point, we orient it in a way, that it reflects the rays from the center of the sun¹ directly on the sun.² But until now, we have ignored the rays which come from the rim of the sun. These rays start at a different position, namely the sun radius (695700 km). Due to different starting position, the rays have a different angle to arrive at the power plant, arcsin(sun radius / sun-earth-distance), which is 0.27°. Now we already oriented the mirrors parts in a way, that the rays from the center of the sun are reflected onto the satellite, but the rays from the rim of the sun come at an 0.27° differing angle. If the incidence of the ray on a mirror is changed by an angle, the outbound ray is also changed by the same angle. This leads reflected rays leaving in a direction 0.27° offset from the direction to the satellite. Assuming the satellite is at a height of 300 km and directly above, it is 300 km away, the smallest realistic distance. With this angle, it leads to a miss of plant-satellite-distance sin(angle) leading to 1.4 km. This thought is valid for all points on the rim. Similarly, the rays between the rim and the center land between the satellite and 1.4 km off target. Hence the plant projects an image of the sun onto the satellite with a radius of 1.4 km.

¹ Well they actually do not come directly from the sun, they still come from very close to the surface, but they seem to come from the center of the sun and for rays it is not important how far they have already traveled. We can just assume the sun is a disc.
² If we assume the mirror is optimally shaped, we can reflect every ray, which seems to come from the center of the sun, perfectly on the satellite. Such a mirror would be part of an ellipsoid, with focal points at the center of the sun and the center of the satellite. In practice, it would be practically indistinguishable from a paraboloid with the satellite (deviance of 1.5 µm with a guessed plant size of 1 km). This is possible as the rays through the center of the sun falling onto the plant are, as you say, almost parallel.

Yes, you are right, considering the rays emerge from a point. And yes, each panel or all panels in unison can act like a magnifying glass. However, if they focus the light on a point at the height of the satellite, they work like a magnifying glass, or telescope with a focal length of the satellite – power plant distance, so at least 300 km. Considering the angular size of the sun, this telescope would lead to an image of the sun, the size of 3 km.

No sun rays are not parallel. If you looked at the sun (don't, it will burn your eyes), would you see it as a point or a disc? As a disc. Why? Because even looking in slightly different directions, you see the sun. So the rays from the sun are not almost parallel, the rays from other stars are, they look point like.

Two interesting images for you: A solar eclipse viewed trough tree leaves: You can see the partial sun disc by using the small free points in the tree cover as pinhole cameras. Sure, the tree cover does not have lenses, but they only make the image sharper, not smaller. In this image the focal length is only the height of the trees and the image is already a few cm across. It also shows that the rays from the sun are not parallel. If they were, all rays going through the small free spots in the tree cover would end up at the same spot on the ground.

International Space Station, ISS, flying in front of the Sun: As the sun and the satellite are far away, we can assume that the angular size of the original sun and the virtual sun image are approximately the same when viewed from the power plant. Hence, this image shows how the mirrors would form an image of the sun, where only a small part of it hits the sun.
As the sun is much larger than the ISS, the angle of rays which come from the sun is much larger than the angle of rays which hit the ISS.

Yes i am, because it is unimportant if the light comes from the sun or the moon or a 3km large satellite (assuming they would have the same radiance). It would be important if the power plant were ten times larger, the satellite would be closer or larger. However in this case the limit to the power is is the etendue of the light at the satellite. The maximum power is the etendue at the satellite times radiant flux of the sun.
If you want a fun and interesting read which does explain a related "problem", there is a relevant xkcd

I could explain it to you in at least five different ways in detail, three of them i have already done in short here in the comments. However, you never argued directly against my point. You don't talk to me seriosly but laugh about it.
This is not what a serious disussion looks like like. If you want an explaination, i would be motiviated to take the time and explain it in detail.
Note that i listened to your point, considered it and argued why it plays no role. You have not considered my explainations.

No i am talking about all the mirrors as one surface, no matter they are really one or consist of small pieces

For the 65 W/m^2 i already used the size of the whole system, so all 10000 mirrors.

The sun has a angular diameter of 32 arcmin. (see here) Hence, the rays hitting one point of the one mirror, have come from different angles, namly filling a circle with this angular diameter. By reflection, the directions of the rays changes. But rays hitting the same spot on the mirror which were misaligned before by 32 arcmin are also misaglined by 32 arcmin after the mirror, independent of its shape. Therefore, the rays emerging from the power plant diverege by at least 32 arcmin. This is not a problem for operation, as this leads to a size of 4.6 m at an estimated maximum distance of 500 m between tower and mirrors. When the mirrors point at a satellite however, a distance of 300 km leads to a beam diameter of 2.8 km calculation

Even an ideal mirror can only project a point source onto a point. It is impossible to focus the rays of an extended source onto one point. See https://en.wikipedia.org/wiki/Etendue if you want to know details. With conservation of etendue you can also calculate this in a similar way.

The problem is the size of the sun. If you could look at the sun (don't, try the moon its approximately the same size in the sky), you see it has a relatively large angular size. Its not just a point in the sky.

So the problem, the rays from one point of the sun are almost parallel. But the rays from the different points of the sun are not. So they also aren't parallel after your mirror. They spread in an angle similar to the size of the sun on the sky. And this is much larger than a satellite. So you cannot focus all energy on a satellite.

It holds if the light spreads wider than the target. So also for directed light sources at large enough distances. Even a perfect mirror must spread the light in the same angle as it is incoming. Hence the beam would at least 3 km wide at the satellite. Therefore the satellite can only recieve a Illumination of ~65W/m^{2 which is a few percent of the normal sun brightness of 1300 W/m}2 in space.

Another way to look at it, the mirrors cant make the sun seem brighter only larger. From the tower you see a large solid angle around you the mirror, therefore, it can seem like you are at the surface of the sun. However, fro. the position of a satellite, the power plant only takes a small solid angle, so it seems like a "smaller" sun. Assuming 400 MW and 1 kW/m^{2 (at surface) solar power, it has an area of 400000 m}2, so a solid angle of 4.5e-6 sr from 300km while the sun has 70e-6 sr. So ten times smaller, therefore weaker. Note however here i did not account for attenuation in the atmosphere

It holds if the light spreads wider than the target. So also for directed light sources at large enough distances. Even a perfect mirror must spread the light in the same angle as it is incomming. Hence the beam would at least 3 km wide at the satellite. Therefore the satellite can only recieve a Illumination of ~65W/m^{2 which is a few percent of the normal sun brightness of 1300 W/m}2.

Another way to look at it, the mirrors cant make the sun seem brighter only larger. From the tower you see a large solid angle around you the mirror, therefore, it can seem like you are at the surface of the sun. However, fro. the position of a satellite, the power plant only takes a small solid angle, so it seems like a "smaller" sun. Assuming 400 MW and 1 kW/m^{2 (at surface) solar power, it has an area of 400000 m}2, so a solid angle of 4.5e-6 sr from 300km while the sun has 70e-6 sr. So ten times smaller, therefore weaker. Note however here i did not account for attenuation in the atmosphere

Yes colors have a meaning. However, they change ober time and culture. So why not use the word which describes exactly what we mean?

I agree, nowadays blacklist/whitelist has practically nothing to do with skin color. However i do think it is weird to use the same words for describing the appearance of people and good/bad.

Well i would be indifferent to the renaming to primary, because it doesn't really matter to me what they call their branches, as long as it is descriptive. primary also conveys the meaning. I would probably continue using main/dev because i see no reason to change.
I am not someone who says "You should change this!". I just say, think of it, there are some reasons to change and the only reason to keep it, os that we did it always like this. I think there are reasons for selecting better words. And I am only annoyed by people who are outraged by things others do, which does not really affects them negatively. I get it that someone wants to continue using blacklist, master, etc. and I am ok with that.

Even ignoring the question of racism, they are still stupid names.

Imagine teaching a child about this and it asks: Why is white allowed and black not? The only answer is, because it is like this for a long time. If we name them allowlist and denylist, it is obvious to all English speaking people. Shouldn't we strive for descriptive names in programming?

However, if you use names whitelist an blacklist, you need to make the implicit connection white-positive black-negative. Yes obviously this does not make you racist if you do this in programming. But is it good?

Yes that is the point. They made the choice to change their default. You can still make the choice to name your branches, especially the main one, as you like. Setting it for a project is less work than complaining about it.

I cannot recommend mindfulness enough, as already suggested by many others in this thread.

I think, you said you are already in therapy? In this case, I would definitely talk with your therapist about this and things you want to adopt beforehand. If you want a simple concrete tip, you could try the "mindfulness coach" by the US department of veteran affairs. I liked it a lot and the apps from there get good privacy recommendations from mozilla.

I am a bit suprised by the many people recommending to just stop giving fucks. Is this what you really want? Or do you just want avoid the emotions of taking control?

You do not need to be that hard to yourself when your feeling "wrong". Yes it is probably better for yourself if you don't overreact. However you cannot really cotntrol your feelings. So it is still better to accept your anger. First, as you said, it drives up the frustration, because now you are also worried about your feelings. And second your original emotion wants to be "noticed". I read and experienced a few times myself, the "wrong" emotion disappears often quickly when you accept it. It is an essential concept of mindfulness, to accept your emotions.

Edit: As far as i understand it and experienced it, saying to yourself "no i shouldn't be angry about this" won't change your thinking

I think I understand you. I also think there are needs for extreme emotional response. However, I would be interested how often they helped you in, and how often the only effect of these was making you feeling worse?

I did some therapy in this direction. And I am generally more content. I can enjoy way more time of my life than a year ago, even in similar situations.
But if we talk about the status of the world, I am at least as angry and sad as before. And I also do at least as much to change it as before. Which, to be honest, is not as much as I would like.

Edit: I think I can actually experience emotions more intense now, while not being overwhelmed by them.

I want to thank you for your messages here. I agree with promethil that you need to consoder yourself, i think texts like yours can do quite something good. Sure you won't heal someone with a few messages. However, I was brought to a mindfulness training* mostly by a reddit chain of comments and this helped me, along other things, a lot, getting out of difficult times.

*An app called "Mindfulness Coach" by the US Department of Veterans Affairs

I understand your point, and I also think a bit in this direction. But i think there may be two counterpoints.

First you beeing depressed over the status and worrying at home and online about it, is not really helping your or doing anything against your boss.

Second, as i understand it, the goal is not to get really content, but to get more control over your feelings. It is perfectly fine if zou feel sad or angry over the situation. It shows you what you want or do not want. But this doesn't need to control your life. If you have the possibility you should definitely use your anger to give you energy for the fight for better working conditions. But if you can not, you should your feelings taking complete control over you

As far is i understand it, yes this is the point of therapy. I mean which problem could your therapist really solve? The can't tell you what to do to get for example a better job.
They can help you to find the root cause of your problems and may help you find a way to solve them. However, as you said, many of the problems can't be solved by oneself. But is it useful to be in depression over this? I don't think so. Is it useful to be sad or angry about this? Yes, i do think so. In principle this feeling shows you, that there is a problem. This anger may help you in some situations to get what you want. I do not think therapists want you to do away with the feelings. But where they want and can help you, is that these feelings do not take full control over your thinking. For example, when you a lie in bed, these feelings do nothing good.

relevant xkcd

I recently started reading the discworld series by Terry Prattchet and I'm really enjoying it. It has just so absurd humor.

Your book reminded me of "Harry Potter and the methods of Rationality", which i read a few years ago. The setup is lously based on Harry Potter, however Harry tries to take a scientific and rational view on magic. It is one of my favourite books.

I don't know your exact experiences, but I had a similar feeling in the past. However, recently I noticed it was a lot of how i behaved to them. I started speaking more openly with my male friends and noticed, they also value my emotions. The main difference was, that my friendships with women started on an emotional level making it a lot easier to open up for me. With my male friends, I needed to just say how i feel, which i have not dared for a long time. My own stereotypes probably played a larger role than the gender of the people involved.

However as others have said, if they do not take you seriously when you open up, they are bad friends. (Edit: Bad friends is a bit harsh, more like friends for having fun together, not to rely on. This is also nice even if it can be hard to accept)