H-Astronomy-003.htm

Astronomy 1700-1950

Astronomy Technology

Major contributors during this period were:

Herschel 1768-1823 Maps Milky Way and finds binary stars.

Bunson 1811-1899 worked with Kirchoff

Kirchoff 1824-1887 defined rules for spectral lines

Higgens 1824-1910 Found hydrogen lines in light from stars.

Balmer 1825-1898 “Balmer Lines” atomic signatures

Mach 1838-1916 Concepts on physics used by Einstein

Plank 1850-1947 Planks constant & quantum mechanics

Rutherford 1871-1937 X-Rays

Bohr 1885-1951 Modeled the atom

Einstein 1879-1953 1905 Theory of Reletivity E=mc² Built on Mach’s concepts

Hubble 1899-1953 Measured distances to stars and galaxies. Light spectrum and brightness is message in start light.

Herzsberg 1873-1973 Hersberg-Russell diagram showing life of stars

Russell 1879-1957 above

Shapely 1885-1972 Proved location of the sun in galaxy, not at the center.

Gamo in 1947 proposed the Big Bang concept

Dispersion, Reflection & Refraction of Light

Newton, in addition to defining laws of motion, inertia, gravity paved the way to dealing precisely with light. He discovered that ordinary light is made up of many colors and defined it’s behavior – inventing the reflecting telescope in the process. These discoveries permitted accurate measurements in the field of Astronomy.

Inverse square law of dispersion: Intensity = luminosity / distance squared

Law of Reflection

Law of Refraction

Speed of Light

Speed of Light: = 186,000 miles per second.

Roemer 1644-1710 measured the speed of light using the time required for light, by measuring the time for one of Jupiter’s moons to pass through Jupiter’s shadow when measure from close and far Earth orbit.

Michelson (1855-1931) measured the speed of light used a rapidly rotating mirror with many faces, and a distant fixed mirror. A flash of light from one face of the rotating mirror passed to the fixed mirror, which returned it just in time to be reflected from the next face of the rotating mirror. Michelson could then find the speed of light simply by dividing the distance covered (twice the distance between rotating and fixed mirrors) by the time elapsed, for the mirror to turn from one face to the next. The rotating mirror was on Mt Wilson and the fixed on Mt San Antonio , CA.

Telescope angle method: To keep a telescope on a specific target the telescope must be set at an angle such that light traveling down it’s tube does not hit the sides. Imagine yourself walking in the rain, holding a tube in your hand, for a raindrop to pass through without hitting the side you will need to hold the tube at an angle that matches your speed of walk and the raindrops rate of fall.

Light travels about 5.880,000,000,000 miles in one year. So large is our own Galaxy, we see looking into the Milky Way, that it would take 1,000 centuries for light to travel across it.

From the Inverse square law of dispersion: Intensity = luminosity / distance squared

If the distance to known star is established, then the distance to another star can be determined if it’s “magnitude”, it’s relative luminosity is known. A small close star can look like a far large star – unless by detective work the magnitude of the stars can be determined.

What is light?

The electrons of an atom reside in their normal shell unless excited by heat, light or collision; at which time they can be driven to a higher shell. They drop back to their normal shell state unless energy is applied to keep them in an excited state. When the electrons drop from a higher shell to a lower shell they emit photons. The amount of energy, and the wave length, depend on what shell they come from and drop to. By selection of elements used, computer monitors and light emitting diodes can be created to give off desired colors.

c= speed of light, f = frequency, l = wave length. E=energy of photon, h = Planck’s constant = 6.62 x 10 ^-27 ergs/sec

Black Body Emission/Absorption is given by Stefan-Boltzmann law

E(T) ergs/cm²/sec, s = 5.672 x 10 ^–5 Stephan-Boltzman constant, T in deg Kelvin

What we see as light

Visual Spectrum seen by humans

Light is a form of electro magnetic radiation. Longest waves are radio waves, shortest waves are heat.

Spectrum seen by plants

Three Laws of Spectral Analysis

Kirchhoff’s First Law: A luminous solid or liquid emits light of all wavelengths, thus producing a continuous spectrum.

Kirchhoff’s Second Law: A rarefied luminous gas emits light whose spectrum shows bright lines, and sometimes a faint superposed continuous spectrum.

Kirchhoff’s Third Law: If the white light from a luminous source is passed through a gas, the gas may abstract certain wavelengths from the continuous spectrum so that those wavelengths will be missing or diminished in its spectrum thus produce dark lines.

Examples of the three laws

If the source is moving away the lines will be shifted to the right (longer), if the source is moving toward the observer, the lines will be shift left (shorter)

They were now able to define the sizes of each of the planets in our solar system.

By looking at distant galaxies they could construct an image of our galaxy

1700-1950 was an age of technical and astronomical discovery. Data was being gather in preparation for exploring Einstein’s Theory of Relativity and the entrance into Cosmology. The Big Bang had just been proposed and it was found that Einstein’s model of a static universe was wrong – everything was expanding, moving away from each other.