http://www.upworthy.com/a-smartypants-scientist-makes-an-easy-analogy-about-our-planet-and-now-im-scared

LIGHT IS A FORM OF ENERGY THAT HAS BOTH WAVE AND PARTICLE PROPERTIES.

WE CAN CHARACTERIZE LIGHT BY ITS WAVELENGTH.

VISIBLE LIGHT HAS WAVELENGTHS THAT RANGE FROM 400 TO 700 nm (NANOMETERS).

THE VISIBLE PART OF THE SPECTRUM IS A SMALL PART OF THE ELECTROMAGNETIC SPECTRUM.

THE SUN EMITS MOST OF ITS LIGHT IN THIS REGION, AND OUR EYES ARE ADAPTED TO THIS.

LIGHT ENERGY IS INVERSELY RELATED TO THE WAVELENGTH.

THIS MEANS THAT AS THE WAVELENGTH INCREASES, THE ENERGY PER PHOTON (PARTICLE) OF LIGHT DECREASES.

ENERGY = E = hn = hc/l where h = constant

c = speed of

light

l = wavelength

ANOTHER PROPERTY OF LIGHT IS THAT ANY OBJECT ABOVE ABSOLUTE ZERO EMITS LIGHT.

AS TEMPERATURE INCREASES, THE WAVELENGTH THE OBJECT EMITS SHIFTS TO SHORTER WAVELENGTHS.

SOMETHING THE TEMPERATURE OF A WARM BLOODED ANIMAL (HUMAN) WOULD EMIT IN THE INFRARED.

THE SUN EMITS IN THE UV AND VISIBLE REGION OF THE SPECTRUM.

SOLIDS EMIT LIGHT IN CONTINUOUS BANDS.

GASES EMIT LIGHT AT DISCRETE (INDIVIDUAL) WAVELENGTHS.

THIS IS IMPORTANT, AS ASTRONOMERS CAN USE THE CONTINUOUS SPECTRA OF STARS TO TELL THE TEMPERATURE.

THEY CAN USE THE LINE SPECTRA TO DETERMINE WHAT ELEMENTS THE STAR CONTAINS.

SCIENTISTS USED THE FACT THAT ATOMS IN THE GASEOUS STATE EMIT LINE SPECTRA TO COME UP WITH A MODEL OF THE ATOM.

THE MODEL THAT NIELS BOHR CAME UP WITH IS THE “SOLAR SYSTEM” MODEL OF THE ATOM.

IN IT, THE PROTONS AND NEUTRONS ARE IN THE NUCLEUS AND THE ELECTRONS ARE IN ORBIT AROUND THE NUCLEUS.

IF WE COULD LOOK AT THE DISTANCES INSIDE AN ATOM, WE WOULD QUICKLY REALIZE THAT AN ATOM IS MOSTLY EMPTY SPACE.

IF WE WERE TO EXPAND A HYDROGEN ATOM SO THAT THE PROTON WAS THE SAME SIZE AS A HUMAN, THE ELECTRON WOULD BE AT A DISTANCE OF ABOUT 2 MILES AND WOULD BE THE SIZE OF A SMALL BIRD.

PARTICLE MASS Amu Location ChargeNeutron 1.67 x

10-24

1 Nucleus 0

Proton 1.67 x 10-24

1 Nucleus +1

Electron 0.0009 x 10-24

0 Shells outside nucleus

-1

IMPORTANT FACTS ABOUT ATOMS:

1) THE NUMBER OF PROTONS IN THE NUCLEUS (ATOMIC NUMBER, Z) DETERMINES THE ELEMENT.

2) ALL ATOMS OF A GIVEN ELEMENT HAVE THE SAME ATOMIC NUMBER.

3) ISOTOPES ARE ATOMS OF THE SAME ELEMENT WITH DIFFERENT ATOMIC MASSES (DIFFERENT NUMBERS OF NEUTRONS).

EDWIN HUBBLE, THE ASTRONOMER, NOTICED THAT WHEN HE STARTED STUDYING GALAXIES THAT THE LINE SPECTRA FOR ELEMENTS COULD BE SHIFTED TO HIGHER OR LOWER WAVELENGTHS THAN ONE WOULD OBSERVE ON EARTH.

HE REASONED THAT GALAXIES WITH SPECTRA SHIFTED TO LOWER WAVELENGTHS WERE MOVING TOWARDS US.

GALAXIES WITH SPECTRA SHIFTED TO HIGHER WAVELENGTHS WERE MOVING AWAY FROM US.

THIS IS CALLED THE DOPPLER SHIFT.

HUBBLE ALSO NOTICED THAT EXCEPT FOR A FEW GALAXIES IN OUR IMMEDIATE NEIGHBORHOOD, ALL GALAXIES WERE MOVING AWAY FROM US.

HIS OBSERVATIONS LED SCIENTISTS TO DEVELOP THE BIG BANG THEORY.

IF YOU REWIND THE EXPANSION, YOU REACH A TIME IN THE DISTANT PAST WHERE THE UNIVERSE OCCUPIED A SINGLE POINT IN SPACE, THE SINGULARITY.

SCIENTISTS ESTIMATE THE AGE OF THE UNIVERSE AT 13.7 BILLION YEARS.

INITIALLY THE UNIVERSE CONTAINED HYDROGEN, HELIUM AND A TRACE OF LITHIUM.

ALL OF THE OTHER ELEMENTS WERE FORMED IN THE CORES OF STARS.