AST 115 Day 2
Ch. 1 Discovering the Night Sky
What can we see from a dark site on a clear, moonless night?
It turns out that there are many illusions which we must be careful to interpret properly.
(1st Illusion) The night sky is filled with apparent patt
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Nicholas Copernicus (1473-1543) Poland
He re-proposed the concept if the sun-centered solar system.
His book De Revolutionibus was published in 1543
In it he established the correct order: Sun, Mercury, Venus, Earth, Mars
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5th Illusion Retrograde Motion
Usually a planet moves slowly eastward in the sky with respect to the stars. (Not the daily
motion which carries all objects on the CS toward the west).
However, for a time when the planet is closest to the Ear
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Sun-Earth-Moon arrangement (Full Moon)
1. Penumbral Moon passes through the outer, lighter portion of Earths shadow. Cant
see with eye.
2. Partial Moon passes into the umbra of the Earths shadow, but does not get totally
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Sir Isaac Newton (1643-1727) England
He contributed new ideas to many fields: Optics, heat, mechanics astronomy
He was co-inventor of calculus!
He published important results in his book The Principia included his:
Three Laws of Motion
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Many civilizations have produced a variety of calendars-Maya, Aztec, Anasazi, Stonehengeall
to keep track of the seasons.
Main problem: There are NOT an exact number of days per year.(spins per orbit)
1 year = 365.24219 days
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Properties or Powers of a Telescope
1. Magnification-The ability to make objects look larger and seem closer. cfw_Depends on
focal length of objective
M=Focal Length of objective
Focal Length of Eyepiece
2. Light-gathering Power-The ability
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Phases of the Moon
When the Sun shines on any sphere there is always a sunlit hemisphere and an unlit hemisphere.
Thus, phases are caused as the Moon orbits the Earth and we see a changing portion of the sunlit
Note that the phases of
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Astronauts in the Space Station appear to float around.
Mass x Velocity x Distance from axis = constant
(i.e., angular momentum is conserved)
Newtons revision to Keplers 3rd Law:
(units must be: a in A.U.s, P in years, and M
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What causes the changing seasons on Earth?
Earths rotational axis is tilted ~23.5 degrees with respect to the perpendicular to its orbit.
The seasons are caused by this tilt being maintained throughout Earths orbit of the sun.
Measuring the Distances to the Stars
Stellar parallax = the apparent shift in position of a star as we change our vantage point due to the Earth
orbiting the Sun
Distance= 1/stellar parallax angle d=1/p
Angle must be in arc seconds(")
Stellar Explosions: Observations of Phenomena
Many nearby stars have low luminosity, high surface temperature
companions known as white dwarfs
Ex. Sirius B
Properties of a White Dwarf Star
Diameter: 10,000 km (6,000 miles) *very similar
The True Nature of
Astronomers used to not be aware of other galaxies
Ex. Messier 51 The Whirlpool
Catalogs of Nebulas
The Messier Catalogue: M numbers
NGC = New General catalogue
Herschel and son John)
what are the nebulas?
Cosmology is the
study of the origin, structure, and evolution of the Universe
= everything there is including: stars, comets, planets, gas, and dust,
galaxies, etc, and SPACE
if the universe is
Life Beyond Earth?
Life = carbon-based, water-based
life as we know it
Carbon can join with up to 2 other atoms in long molecules that
have strong, yet flexible bonds.
These organic molecules are plentiful on Earth:
Earth is a water-world covered with vas