Astronomy
Light - form of electromagnetic energy visible to the human eye that is radiated by moving charged
particles
Electromagnetic radient energy – forms of energy that travel at the speed of 300,000 kilometers (186,000
miles) per second, each form having a different frequency and wavelength.
Electromagnetic spectrum – the total range of (visible and invisible) electromagnetic energy
(electromagnetic radiation) waves that is emited by the sun; from radio waves to gamma rays.
Longest - Radio waves – wavelengths up to several kilometers
Shortest – Gamma rays – wavelengths as short as 1/1,000,000 of a centimeter
Visible Light – between Infared and Ultraviolet -- deep red (longest wavelength) to deep blue or violet
(shortest wavelength)
Energy emitted by the sun (sunlight) at the Earth’s surface:
~ 50% is visible electromagnetic waves
~ 3% is ultraviolet
~ 47% is infrared
Spectroscopes – a telescope that uses a prism to separate visible light and determine the chemical
composition of a star
Astronomical Unit (AU) – distance from the earth to the sun, ~ 150,000,000 km (~93,000,000 miles)
Light speed - 299,792,458 meters per second (about 186,000 miles per second)
Light year – distance that light travels in one year, at approximately 300,000 km/sec (186,000 mi/sec), or
9,461,000,000,000 km (5,880,000,000,000 mi).
[One parsec is equal to 3.26 light-years and to 206,265 astronomical units]
Stars
Star – point of light in the night sky; massive shining sphere of hot gas
Constellation – group of stars that appears to form a pattern in the sky
Circumpolar constellations – constellations that appear to never set below the horizon in the
northern latitudes (Ursa Major, Ursa Minor, Cassiopeia); appear to circle clockwise around Polaris,
the northern star.
Mass, size …. Density
Smallest stars are smaller than the earth
Largest stars are over 2,000 times larger than our sun
Color
Ranges: red (cooler) to blue (hottest) – depends on the star’s surface temperature
Composition
Determined by spectrum analysis: mainly hydrogen & helium
Brightness
Apparent magnitude – brightness as seen from earth with the unaided eye (brightest <1; faintest >6)
Luminosity – true brightness, depends on size and temperature
Absolute magnitude – expresses luminosity of stars as if they were seen from the same distance –
32.6 light years from Earth. (our sun = 4.8; average vs. Rigel = -6.4)
Life Cycle of a star
Big Bang Theory – the universe began to expand with the explosion of concentrated matter and energy and
has been expanding ever since. 15 to 20 billion years ago an explosion shot concentrated matter and energy
in all directions.
Origin of a Star
Nebula – huge cloud of gas and dust in space
Gravity caused the gas in the nebula to contract to form a protostar
(Protostar – very young star that is not hot enough to shine by nuclear fusion)
As gravity packs matter more tightly – the protostar’s temperature rises until it reaches a
temperature high enough for nuclear fusion to begin.
Nuclear Fusion – 2 hydrogen nuclei fuse together to create 1 helium nuclei and releases
electromagnetic radiant energy as a by-product)
Main Sequence Stage
When the release of electromagnetic radiant energy (pushing out) reaches a balance with the
gravity (pulling in) the star stops contracting and reaches the stable state.  main sequence star
a star will remain constant will remain fairly steady until the hydrogen is used up and the star will
collapse without the radiating energy
Our sun is a main sequence star for 5 Billion years and will be using up its hydrogen for about 5
billion more years – it will change little during that time
The original mass of the star determines its temperature and the color: large – glows blue; medium
– glows yellow-orange; small – glows orange
Final Stages (dependent on mass)
Red Giant, Giant or Super Giant - the hydrogen is used up, the core’s temperature goes as high as 100
million ºC the star expands. Nuclear fusion begins: helium(3) to carbon(1).
White dwarf– when the helium is used up, the giant collapses and the nuclei squeeze together.
Nova – sometimes a white dwarf flares up brilliantly for a short time and then fades.
Surper nova – fusion continues until the core becomes iron; the star cools and collapses. During the
collapse, the pressure and temperature within the core increases dramatically – iron gets fused with heavier
elements. The speed of the collapse increases and the star explodes - temperature is so hot that it explodes
to incredible brightness. The explosion blasts much of the star’s matter into space.
Neutron Star – contraction of remaining matter after a supernova explosion. This matter is extremely
dense – 1 teaspoon of a Neutron star weighs more than all the people on earth.
Pulsar – a rotating neutron star, radiation is received in regular rapid pulses
Black hole – the most massive stars, after their super nova, collapse into a very small volume. The gravity
is so strong that light cannot escape.
Telescopes;
 can collect far more light than the unaided eye
 can magnify images
Optical Telescope – use lenses and mirrors to gather and focus starlight
Refracting Telescope – bends or refracts starlight through the first lens to focus the image through the
second lens, the eye piece
Reflecting Telescope – uses one large curved mirror to focus starlight
Multiple-Mirror Telescope (MMT) – many reflecting mirrors working in unison to produce larger, higher
resolution images
Schmidt Telescopes – uses both reflecting mirrors and refracting lenses
Hubble Telescope – reflector orbiting Earth, unparalleled resolution and usable for ultraviolet detection
that isn’t possible at the surface
Electromagnetic Spectrum – the entire range of visible and invisible electromagnetic waves, from radio
waves to gamma waves
Spectroscopes – telescope that uses a prism to separate visible light and determine the chemical
composition of a star
Radio Telescopes – very large telescope that picks-up radio waves emitted by quasars and pulsars
Solar System: system of nine planets & many other objects that orbit our sun
Inner Planets – Terrestrial Planets: the 4 solid, rocky planets closest to the sun
Mercury: 1st planet,
moon-like in appearance,
4500C during the day, -1750C at night,
orbital period – 88 days,
turns on its axis once every 59 days,
no atmosphere,
weak gravity
Venus: 2nd planet, Earth-like,
dense CO2 atmosphere (runaway greenhouse effect),
clouds of concentrated sulfuric acid,
surface pressure 90 times greater than the earth.
Earth: 3rd planet,
150 million km from the sun, or 1astronomical unit (AU)
nitrogen –oxygen atmosphere
only planet where water is abundantly present in all three states
23.5 degree tilt from vertical
Mars: 4th planet,
red iron-oxide surface
687 days orbital period
270C during the day, -1250C at night,
95% Carbon dioxide atmosphere
polar ice caps and layer of subsurface permafrost exist
Outer Planets – Jovian Planets (gas giants): the 5 planets farthest from the sun (the first 4 are very
large and made up of predominantly gas)
Jupiter: 5th planet – Jovian planet,
largest in solar system,
gas planet composed of liquid hydrogen, helium & some ammonia, methane and water vapor
11.9 earth years orbital period
rotates once every ten hours
striking feature: The Great Red Spot
strongest known magnetic field
Saturn: 6th planet – Jovian planet,
Extensive ring system
lowest density, gaseous (could float on water – if there ever was enough)
orbital period 30 earth years
rotates once every 10.7 hours
Uranus: 7th planet – Jovian planet,
gas planet with rotation axis almost parallel to its revolution plane
84 year orbital period
surface temp -2000C
rotates once every 17.2 hours
magnetic field in 60 degrees from its orbital axis
Neptune: 8th planet – Jovian planet,
gas planet similar to Uranus
methane gas giving the blue color
rotates 16.1 earth hours
orbital period 165 earth years
Magnetic field is tipped 47 from rotational axis AND offset from the center of the planet
Surface temp -214C
Pluto: 9th planet,
dense atmosphere surrounds a solid, rocky surface
smallest and coldest ‘planet’
orbital period 248 years
highly elliptical orbit (inclined 17 degrees)