Famous people: Galileo Galilei

for Christmas I got some nice books and now I am reading first one which is called: 10 Physicists who transformed our understanding of reality. It seems that it is very good book and I am behind the first chapter which was about Galileo Galilei so I decided that I will write about him.

So Galileo Galilei is very famous astronomer but why? Because of Galilean moons, yes that is right and also because of his first telescope and probably even because of his conflict with church.
Galileo technikou vědecké metody učinil významné objevy ve fyzice a astronomii.Galileo was born 15.2.1564.
It was time when most people thought that everything is made up of four elements and the fifth, quintessence was present in the sky. Not many people questioned those ideas. Lot of stuff was based only on thinking because it was thought that sense was easily fooled in experiment.

Galileo was born in Pisa to his father who was lute player. First he wanted to be priest but father rather wanted him to become a doctor.
Galileo had private teacher as did other mid class kids and soon he discovered that he was more curious about science than in priesthood.

He started to visit university in Pisa when he was seventeen.
There are some stories about his curiosity for all the things around, like throwing stuff from the Pisa tower or watching how pendulums swing.

For example he soon discovered that it is not true that bigger things will hit the ground first like Aristotle thought.

He left the university because his biggest concern clearly was not medicine but rather mathematics. He took some courses to become professor.

In 1595 he started to investigate the problem with tides. Nobody was able to explain them properly before because they were such a strange event, high and low tide twice a day.. geocentric model which was the only one recognized back then was not able to explain it.

This seems to be the first time that Galileo started to think about the heliocentric model first proposed by Copernicus.
Galileo wrote Kepler when he read his pro-heliocentric book. They were writing letters to each other for some time when Kepler told him that he should try to investigate stellar parallax[1].

Galileo finally did not even try because he thought that there are already people, who tried hard enough so he would not be able to measure it. It was measured for the first time in the year of 1838.

Instead of investigating stellar parallax he returned to pendulums and started to make experiments about their swing. It seemed like paradox that no matter the angle of the swing the swing will always take the same time. This was about when he discovered the first law of motion and inertia.

In geocentric model it is thought that Earth is the middle of Universe with everything rotating around it in some kind of shells. The sky is unchangeable so everything that changes must be in sub-lunary sphere[2].

It was October 1604 when supernova was seen from Earth. Galileo thought it is new star but he “knew” that the sky can not be changed so it hat do be in atmosphere where he would clearly see that parallax which I mentioned earlier.

Galileo measured its position on few places in Europe and it did not change, so clearly this model of world was wrong.

After this he constructed his best telescope with magnification of 20x. First of all he found out that the surface of Moon is not smooth as it was thought. Then finally he started to watch Jupiter.

First of all he saw three star like object around it. He thought that those are just normal stars but few days later one of them disappeared and another was visible. This was how he found Galilean moons.

It was another breakthrough since before it was thought that everything has to be orbiting Earth.
Another thing that ensured him of heliocentric model was Venus. He found out that Evening Star also goes through the cycle of “new moon” and “full moon” as Moon does. This was not possible if Venus should be orbiting Earth and at the same time rise as evening and morning star. Also he found out that when Venus is going to be in full moon it is also smaller than in new moon (it is farther away!).

The problem with these revolutionary ideas was that it was clear that church wont like to hear it.
First he only said it to Kepler but than he wrote some books.
Galileo was deeply religious man so he did not want to discredit church but rather show that there were some “small” mistakes.

Galileo thought that when he will show both sides of argument it will be perfectly fine but finally church called him for trial in Rome.
The final sentence was to put him under home arrest and that he will have to rewrite the offensive parts of the book.

I read that there is myth that when they said that he was to be at home arrest he said: “And yet it moves. (the Earth)” but as they stated in the book, he was not stupid to mutter such a thing and there is no evidence for it.

He died in January 8th 1642.

Galileo clearly was really great mind who not only explained perfectly heliocentric model but also showed the ways modern science works.


Galileo Galilei picture.

[1]Stellar parallax is something you see everyday and it has to do with the position of the things around you. When you are driving car the stuff close to you is moving faster than the stuff which is far away from you. It is called stellar because of the different parallax when you are looking from various point on the orbit of Earth.

[2]Sub-lunary sphere is what lies under the orbit of Moon. It is changeable while supra-lunary sphere is what is above the Moon’s orbit. It is regular and it can not be changed.

Moons of our Solar System: Callisto

here it comes, here it goes after a lot of other posts I have decided to write again about moons and this time I continue to really cold piece of giantic rock and 2nd biggest moon of Jupiter and 3rd largest in whole Solar System right after Titan. It is Callisto not The Spear of Vengeance.

Měsíc CallistoCallisto was found with other Galilean moons by Galileo Galilei and independently Marius. Marius gave her this name. Instead of Callisto, Jupiter IV was used. I am really glad that it changed.
Callisto was one of many lovers of Zeus or Jupiter for Roman`s.

As you can see on the picture below, Callisto is really just a little smaller than Mercury.
It is smaller just by few kilometers but it has just a third of Mercury`s weight. As you can see it depends a lot on the stuff from which the object is made.

Callisto orbits at really big distance. 1.88 million kilometers which is almost 1/75 of the distance between Sun and Earth. For moon it is a big number, more than 4 times between Moon and Earth.

It is actually very important that it is so far away because the rest of the Galilean moons are orbiting in resonance which means that they are creating heat in their interior because of friction of the liquids inside.

Callisto can be described as very cold and hard place. There is no volcanism or tectonic activity on its surface to smooth all the features. But there are also no mountains since they are caused by tectonic activity.
Only things you can find there are craters and there is lot of them. Actually the number can not increase a lot because they will almost always overlap so the ones that are old will erode and disappear.

Crater which you can see on the right is called Valhalla crater and this one is the largest. The middle is only 600 kilometers wide but with the rings from the rest of the collision you can say that Valhalla has 1800 kilometers. Another huge guy is Asgard with 1600 km.

The surface is very old and also very cold with temperatures oscillating between -130 and -190 degrees of Celsius.
Most of the surface is covered by water ice.

Under the surface it is assumed that there is thick salty ocean.

Callisto has really thin atmosphere which is made up of carbon dioxide which is the same for Mars. The atmosphere is actually so thin that it has to be powered from dry ice which is evaporating from surface, otherwise it would disappear completely.

There is mission planned to go for Galilean moons in 2020. It is called Europa Jupiter System Mission and it would be founded by NASA and ESA (European Space Agency). More than Callisto, Europa is the moon of interest since there is much higher probability of live because there is this heat from friction.


1st and 3rd picture
2nd picture

Moons of our Solar System: Jupiter´s moons, Prologue

today I will continue to write about moons. Now I will be stucked on the moons of Jupiter for while since it seems that there are about 8 worth a separate posts so this will take some time and today I will try to introduce them.

So for now there are 67 confirmed moons of Jupiter which is most in the whole Solar System. They are named after Jupiter/Zeus´s lovers daughters etc.
After while we run out of those names so we started to repeat them with little changes like: Ganymede>>Ganymed
Callisto>>Kallisto and so on. All moons of Jupiter are tidaly locked.
Those moons are in different groups and the most important are Galilean moons.

Galilean moons are four moons discovered by Galileo Galilei. He discovered them in the year of 1610 even that there are some informations saying that before him chinese https://upload.wikimedia.org/wikipedia/commons/5/5a/Galileans.PNGastronomer found them. What is sure is that independently day after Galileo, Simon Marius found them too and he was the one who gave them the names we use now (before we called them Jupiter I, Jupiter II…).
From left to right you can see on the picture: Io, Europa, Ganymede, Callisto. All of them except Callisto interact through gravitation, they heat each other´s interior through friction.

On the right you can see Galilean moons from Celestia with their orbits. The pie graph shows mass of moons.
Second group really worth mentioning is Amalthea group (beatiful name). Those are inner satellites which orbit really closely to Jupiter.
Members of this group are: Amalthea, Thebe, Adrasthea, Metis.

Amalthea PIA02532.pngBelow you can see picture of Amalthea.

On last picture are the other moons with their irregullar orbits, there arises a question how much should they be considered moons when they are so small.


Pictures taken from:
https://en.wikipedia.org/wiki/Moons_of_Jupiter —> here you can find table of all Jupiter´s moons.

Crash Course video Jupiter´s moons