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Old 06-30-2015, 06:47 PM   #1
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Default Galileo Galilei

Hello, recently I have been watching lectures on modern-history which are presented by a professor from the Great Courses, and one thing really puzzled me. How could Galileo see the moons of Jupiter with such low magnification (x30)? Over the internet I've read that you need at least x100 magnification power to see Jupiter.

How was this accomplished?
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Old 06-30-2015, 08:19 PM   #2
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Default Re: Galileo Galilei

Because you don't need 100x to see Jupiter. You can probably see Jupiter and its moons with a pair of binoculars. You need ~100x to see significant detail in Jupiter , in which case you want a telescope. (at 30x it'll be a disk without any features)
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Old 07-09-2015, 10:46 AM   #3
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Default Re: Galileo Galilei

I was looking at planets once and they just moved to fast to look at in the telescope :/
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Old 10-29-2015, 01:22 AM   #4
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Default Re: Galileo Galilei

Hmm, okay... My other question would be how could he see the sun-spots without going blind? According to this website, he had done several very detailed drawings on different days looking through his telescope: http://galileo.rice.edu/sci/observat..._drawings.html
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Old 10-29-2015, 09:48 AM   #5
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Default Re: Galileo Galilei

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Hmm, okay... My other question would be how could he see the sun-spots without going blind? According to this website, he had done several very detailed drawings on different days looking through his telescope: http://galileo.rice.edu/sci/observat..._drawings.html
Because everything on the internet has to be true right? wow for a paranoid person your not so paranoid
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Old 10-29-2015, 10:39 AM   #6
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Default Re: Galileo Galilei

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Hmm, okay... My other question would be how could he see the sun-spots without going blind? According to this website, he had done several very detailed drawings on different days looking through his telescope: http://galileo.rice.edu/sci/observat..._drawings.html
The link says Galileo made series of drawings of sunspots on the sun. It doesn't mention his telescope or looking through it. It turns out Galileo did use his telescope but didn't look through it directly at the sun. You're right, that would cause damage to your eyes. Instead he apparently used his telescope to project an image of the sun inside his house. I found this info here
http://galileo.rice.edu/sci/observations/sunspots.html
It's not entirely clear from the link exactly how he set up the telescope, but it's definitely a thing you can do. (on another note it's entirely possible to make naked eye observations of the sun in cases in which the sun is partially obscured. e.g. clouds or the horizon. This has been happening for literally centuries before Galileo)

Also @flatoutlie: if the info is published by Rice, more often than not the info is legit.
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Old 10-29-2015, 05:21 PM   #7
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Default Re: Galileo Galilei

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Because everything on the internet has to be true right? wow for a paranoid person your not so paranoid
I am not paranoid! I'm simply curious about how he could achieve such an action as looking through his telescope to look at sunspots and obviously that wasn't the case. Though I've heard during watching lectures of historians and astronomers, Alex Fillippenko for one, that the story of Galileo's sun spotting experience was done through him looking through a telescope, though I could be wrong. I have to re-watch these lectures to make sure. Not everything is as it seems, and I am just trying to find an explanation for such a case. Being paranoid is by checking every packet of food for traces of titanium, this is not paranoia but curiosity of a strange case.

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Old 10-29-2015, 07:44 PM   #8
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Default Re: Galileo Galilei

Sea monkeys response sounds right
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Old 10-29-2015, 09:09 PM   #9
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Default Re: Galileo Galilei

But it would be interesting if they had invented a sunlight filter back in the 17th century. We don't always know a lot of what happened in our history. There are cases like this: https://en.wikipedia.org/wiki/Antikythera_mechanism And sometimes we have no idea how such an old civilization could have created this when this sort of precision was only officially achieved in the modern era. Curiosity, not paranoia.

Last edited by REACTOR; 10-29-2015 at 10:08 PM. Reason: 17th not 16th century
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Old 12-18-2015, 05:48 PM   #10
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Default Re: Galileo Galilei

On the topic of the sun, I'm wondering how much of its power would be reduced if it reflected on a shiny surface such as water/metal and a dull surface such as paper? And also, what is the least amount of power the sun must be reduced be in order to watch it safely for an hour? I tried searching for it on the internet, and looking back at my lectures, but I found nothing on it.
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Old 12-19-2015, 02:39 AM   #11
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Default Re: Galileo Galilei

The amount of power reflected is predicated off of material properties of the object being reflected in question. It has to do with the composition of the object, and it depends on what frequencies of light are converted into thermal energy (not heat), and which frequencies are reflected off of the object. Coincidentally this is how color works. Certain materials are very close to reflecting all light - they're used to reflect light into solar panels in order to use less solar panels.

Your second question is much harder to figure out. It has a bunch of factors - composition of the light in question, and how intense it is, and your eye, specifically its luminosity function. It turns out your eye sees light as more or less bright depending on it's frequency - even if the light is at the same intensity. This is why there's significant work put into computer monitors to adjust for this. Additionally there is the issue of intensity which varies over time and longitude. Angle of incidence is a pretty big deal - and is the reason we have seasons. Lastly there is of course the amount of atmosphere the light has to travel through to get to you which is important because of Raleigh scattering.
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Old 12-19-2015, 09:00 PM   #12
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Default Re: Galileo Galilei

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Originally Posted by seamonkey View Post
The amount of power reflected is predicated off of material properties of the object being reflected in question. It has to do with the composition of the object, and it depends on what frequencies of light are converted into thermal energy (not heat), and which frequencies are reflected off of the object. Coincidentally this is how color works. Certain materials are very close to reflecting all light - they're used to reflect light into solar panels in order to use less solar panels.

Your second question is much harder to figure out. It has a bunch of factors - composition of the light in question, and how intense it is, and your eye, specifically its luminosity function. It turns out your eye sees light as more or less bright depending on it's frequency - even if the light is at the same intensity. This is why there's significant work put into computer monitors to adjust for this. Additionally there is the issue of intensity which varies over time and longitude. Angle of incidence is a pretty big deal - and is the reason we have seasons. Lastly there is of course the amount of atmosphere the light has to travel through to get to you which is important because of Raleigh scattering.
Oh, I see. Well thank you for that insight seamonkey.
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