Understanding “Heavenly Bodies” Day
Over the years, we have had some April 28 heroes who have added to our understanding of the solar system.
Here are three: 
On this day in 1686, the first volume of Isaac Newton’s Principia was published in London, England.
The two-volume work had a Latin name that translated into Mathematical Principles of Natural Philosophy; when we call it Principia, we are just shortening the title to “Principles.”
The masterpiece explains Newton’s laws of motion and his law of universal gravitation, thereby setting out the foundation of “classical mechanics,” or classical physics. The word classical here means physics before Einstein’s special relativity and before quantum mechanics.
Newtonian principles are mathematical, but they are easier to understand than relativity or quantum physics because they generally deal with things that are medium sizes and that go medium speeds—and we’re used to that medium world. When we hear about relativity’s effects of super-fast speeds, they just seem wrong, and when we learn about the quantum world of teeny-tiny particles, that seems confusing and wrong, too.
Apparently, one reason we even have Principia is because of a bet among three intellectuals. Architect Christopher Wren, “naturalist philosopher” Robert Hooke, and astronomer Edmund Halley made a wager about who could get Kepler’s laws about planetary motions from a law of gravitation. Wren offered a prize of 40 shillings (which was about two weeks’ pay) for the winner.
Hooke claimed he had the proof but didn’t want to spoil the others’ fun by showing it to them. He never did show them, though, and we can assume that he had never proved it. In the meantime, Halley really wanted to solve the problem, and finally, about half a year after the wager was made, he visited his friend Isaac Newton and told him about the bet.
Newton had already done the math and had computed the elliptical orbits of the planets. He’d done it 20 years before and had never published it or even shown it to anybody! 
Apparently Newton found it hard to find his notes, but he came up with the equations again, and a few months later he showed Halley the equations. Halley was so impressed that he begged Newton to publish. Newton holed up in his house and wrote for the better part of two years, and Principia is the result.
The funding for publishing Newton’s book had dried up because the Royal Society had had a very costly flop called The History of Fishes the year before. Halley paid his own money to get Newton’s book published—and he was paid back in copies of The History of Fishes!!!
On this date in 1900, Jan Hendrik Oort was born in the Netherlands.
He grew up to be a physicist and astronomer who is most famous for two hypotheses: he suggested that the Milky Way galaxy was rotating (evidence has since shown that this is the case), and he suggested that there is a cloud of comets and other material at the outer edge of the solar system. Now called the “Oort Cloud,” this gigantic area may contain several trillion icy objects, and every once in a while, something comes close enough to the solar system that its gravitational influence “bumps” one of them out of the Oort Cloud and down to inner solar system, where we can see it as a comet traveling around the sun in a very stretched-out oval orbit.
On this date in 1928, Eugene M. Shoemaker was born in Los Angeles, California.
He grew up to be a planetary geologist who contributed to our understanding of the moon, asteroids, and comets. He discovered the Shoemaker-Levy comet, and he named the moon’s layer of soil and broken rock regolith. He studied impact craters and the impact of “his” comet with Jupiter in 1994. While looking for impact craters on earth, Shoemaker tragically died in an auto accident in 1997, and in 1998 a small capsule of his ashes were launched aboard Lunar Prospector to the moon. The brass foil wrapping of the memorial capsule has a quote from Romeo and Juliet:
“And, when he shall die
Take him and cut him out in little stars
And he will make the face of heaven so fine
That all the world will be in love with the night
And pay no worship to the garish sun.”
So far, Shoemaker is the only person “buried” on the moon.
Match ‘Em Up, Up, Up
For millennia, people have been looking up, up, up into the night sky and wondering about the wheeling and wandering lights they saw there. Match up each of the “heavenly bodies” below with their definitions:
1.asteroid
2.comet
3.galaxy
4.moon
5.nebula
6.planet
7.star
DEFINITIONS:
A. an enormous ball of gas undergoing fusion or burning
B. a relatively small body, usually rocky, that circles the Sun
C. a body that circles a planet
D.a body that circles a star that is round and that is large enough to clear its orbit of other bodies
E. a relatively small body made mostly of ices, usually on a long oval orbit around the Sun; when it nears the sun, it displays a “head” and “tail” made of the ice burning off into a gas
F. a huge collection of stars held together by gravity, often in a globular or spiral shape
G. a “cloud” of gas in space
ANSWERS:
1.B – 2.E – 3.F – 4.C – 5.G – 6.D – 7.A
Play space games on NASA’s website.
- Here is a fun “slider” puzzle with beautiful photos of nebulae and galaxies.
- Type space words in this tricky but fun game.
- Try this quiz game about comets.
Read a space book about the planets of the solar system.
There are other space books to read here.
