Happy Pi Day everyone.
From Wikipedia’s post on Uranus:
Sir William Herschel announced its discovery on March 13, 1781, expanding the known boundaries of the solar system for the first time in modern history. This was also the first discovery of a planet made using a telescope.
Sir William Herschel was not the first person to observe Uranus – John Flamsteed beat him to it. But Flamsteed did not recognise Uranus for what it was. The credit for the discovery therefore goes to Herschel.
Utklipp fra Wikipedia’s entry for Galileo Galilei:
On 7 January 1610 Galileo observed with his telescope what he described at the time as “three fixed stars, totally invisible by their smallness”, all within a short distance of Jupiter, and lying on a straight line through it. Observations on subsequent nights showed that the positions of these “stars” relative to Jupiter were changing in a way that would have been inexplicable if they had really been fixed stars. On 10 January Galileo noted that one of them had disappeared, an observation which he attributed to its being hidden behind Jupiter. Within a few days he concluded that they were orbiting Jupiter. He had discovered three of Jupiter’s four largest satellites (moons): Io, Europa, and Callisto. He discovered the fourth, Ganymede, on 13 January. Galileo named the four satellites he had discovered Medicean stars, in honour of his future patron, Cosimo II de’ Medici, Grand Duke of Tuscany, and Cosimo’s three brothers. Later astronomers, however, renamed them Galilean satellites in honour of Galileo himself.
The significance of the above is the following…
This was one of the earliest known astronomical observations using a telescope. The discovery that Jupiter had moons orbiting it was pivotal in displacing the Aristotelian Cosmology which held that all heavenly bodies circle the Earth. This discovery supported the Copernican model of the Solar System where the Sun and not the Earth is at the centre. Galileo’s discovery in September of the same year that Venus displayed phases like the Moon showed that Venus orbited the Sun, not the Earth.
Johannes Kepler (1571-1630) played a major role in the scientific revolution. He is best known as the discoverer of the three Laws of Planetary Motion. He did this by studying the observations made by Tycho Brahe (1546-1601) of planetary motion.
Kepler was instrumental in replacing our Geocentric – Earth centered – view of the Universe with a heliocentric – Sun centered – view. This heliocentric view would later fall. Two major mileposts on our way towards a modern view of our Universe.
Kepler’s three laws are stated in our times thus:
The orbit of every planet is an ellipse with the sun at a focus.
A line joining a planet and the sun sweeps out equal areas during equal intervals of time.
The square of the orbital period of a planet is directly proportional to the third power of the semi-major axis of its orbit. Moreover, the constant of proportionality has the same value for all planets.
The first law describes the shape of a planet orbit. The second law tells us that a planet moves faster when closer to the Sun than when further away. The third law tells us that the length of a planet’s year depends on its distance from the Sun. The further out a planet orbits the Sun; the longer its year is.
Isaac Newton was later able to derive these laws using his Theory of Gravitation.
Did you notice that a Scientific Law describes how natural phenomenon behave?
A Scientific Theory on the other hand explains why things follow the laws they are observed to follow.
The scientific use of the words law and theory differ from the common use of these words. In common use a Law is a rule agreed upon by common agreement and a theory is an untested idea that has not been proved. In common use a theory is weaker than a law. In science the opposite is true.
Note that scientific theories are never proved to be true. Theories can either be proved false (rare) or (more commonly) replaced by a new theory that explains natural phenomenon even better. Newton’s Laws of Gravitation have not been replaced by Einstein’s General Theory of relativity. Relativity is just more accurate than Newton’s Theory in extreme situations. When sending a probe to the Moon; Newton’s Theory of Gravitation works just fine. Sending a probe into orbit round a black hole on the other hand would require use of Einstein’s General Theory of Relativity because the velocities in question are much closer to the speed of light and therefore more extreme.
Ada Lovelace (Augusta Ada King, Countess of Lovelace) was born this day in 1815.
The following quote is taken from Wikipedia’s entry for Ada Lovelace.
She is mainly known for having written a description of Charles Babbage‘s early mechanical general-purpose computer, the analytical engine. She is today appreciated as the “first programmer” since she was writing programs — that is, manipulating symbols according to rules—for a machine that Babbage had not yet built. She also foresaw the capability of computers to go beyond mere calculating or number-crunching while others, including Babbage himself, focused only on these capabilities.
Programming language Ada was named after her.
Now the largest spacecraft ever built, the orbital assembly of the space station began with the launch from Kazakhstan of its first bus-sized component, Zarya, on Nov. 20, 1998. The launch began an international construction project of unprecedented complexity and sophistication.
In the photograph above of the International Space Station, Zarya is the third “bit” from the bottom. It’s solar panels are folded up. below it is Zvezda with it’s solar panels ‘horizontal’ and below that is ESAs Automated Transfer Vehicle Jules Verne with it’s X-shaped solar cells. Jules Verne has been deorbited so it is no longer docked to the ISS. Below is a detailed image of Zarya.
The orbit of ISS is inclined about 51-52 degrees which means it never passes directly overhead where I live (above 60 degrees North). Here we see it passing in the South low on the horizon about every 14 days or so. Even so it is great fun to see this man made object brighter than the brightest stars. I visiteed the South of France earlier this year and had the opertunity of watching the ISS pass over the zenith. Jules Verne was about to dock so we saw that pass over about 10-15 degrees in front of ISS. The ISS has been continually staffed since 2nd November 2000. Think about that. Humans have been continually in space for the last eight years.