Astronomy 1

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Astronomy 1

• Midterm 1 Review

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Scientific Method

• demands systematic observations
• uses mathematically based theories
• experimentally tests ideas
• is subject to independent verification

• Observe, theorize, predict, test, modify!

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Pseudoscience vs. Science

• Pseudoscience does not use the scientific method
• Science uses the scientific method

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Constellations are maps in the sky
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Astrology or Astronomy?

• Uses the positions of planets to predict human
  behavior
• Is a branch of Physics
• Uses the scientific method to interpret
  observations
• Is considered a pseudoscience
• A detailed study of all the celestial bodies in
  the Universe, including planets, moons, stars,
  galaxies, etc.
• Associates the signs of the zodiac with
  personality traits

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A Few Definitions

• planet A celestial body of substantial size
  (more than 1000 km across), basically
  non-radiating and of insufficient mass for
  nuclear reactions to ever begin, ordinarily in
  orbit around a star.
• solar-system A collection of celestial objects
  (e.g. planets, comets, asteroids) orbiting around
  a common star
• galaxy A collection of stars, gas, and dust
  that are gravitationally bound together
• Universe Consists of everything around us

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Sizes
From smallest to largest...
planet
star
solar system
galaxy
Universe
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Scientific Notation

• express very small or very
• large numbers in powers of ten
• Format . X 10
• Rule count the number of zeros to the
• left or right of the decimal point

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The Finite Speed of Light
Average Distance from the Earth to the Sun ?
Astronomical Unit
1 A.U. 1.5 X 108 km
Distance that light travels in a year ? Light Year
Because of the finite speed of light, we are
able to look backwards in time!!!
Thus, the more distant the object, the longer it
takes for the light to reach us and the further
back in time we are looking!!!
The finite speed of light gives us a fossil
record of the history of the Universe!!!!
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These coordinates can be used to describe the
position of stars locally
Altitude angular distance of object from the
horizon
Azimuth angular distance with respect to North
Zenith the point that is straight up above you
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Celestial Sphere Imaginary sphere that
surrounds the Earth Celestial Equator circles
the sky on the celestial sphere halfway between
the celestial poles (analogous to Earths
equator)
Right Ascension Lines that cross the celestial
equator perpendicularly and goes through the
North and SouthCelestial Poles (analogous to
longitude lines)
Declination Lines that are parallel to the
celestial equator (analogous to latitude lines)
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Motion of the Stars
Earths counter- clockwise rotation also causes
the Sun and stars to appear to move from East to
West
There are no West and East Stars only the North
Star remains fixed in the sky!!
We cannot see the South Star from the Northern
Hemisphere!!!
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Motion of Stars at the Equator
Motion of Stars at the North Pole
The North Star is located at the zenith!!
The North Star is located at the horizon!!
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What about the Sun? It seems to move across the
celestial sphere on a path called the ecliptic.
The ecliptic is also the path of the Earths
orbit around the Sun
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The seasons are caused by the tilt of the Earths
axis of rotation
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Seasons

• Summer Solstice Sun is highest in the sky
• at noon, more than 12 hours of sunlight
• Winter Solstice Sun is lowest in the sky
• at noon, less than 12 hours of sunlight
• Equinox during spring and autumn equal days and
  equal nights

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In other words ...

• The Earths rotation on its axis determines the
  length of the day
• The Earths orbit around the Sun (revolution)
  determines the length of the year
• The Earths 23.5o tilt with respect to the
  ecliptic causes the seasons.

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Precession is a slow, circular motion of the
Earths axis of rotation witha period of
26,000years
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Although the Moon is always ? lit from the Sun,
we see different amounts of the lit portion from
Earth depending on where the Moon is located in
its month-long orbit.
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Eclipses occur only when the Moon crosses the
ecliptic during the new or full phase
But they do not occur every month because the
moons orbit of revolution is inclined 5 degrees
with respect to the ecliptic.
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Lunar eclipses because the Earth blocks the light
from the sun from hitting the moon!
Lunar eclipses happen when the moon is in the
full phase!
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Lunar Eclipses
The moon is not completely dark during a total
lunar eclipse since small amount of light is bent
around the edge of the Earths atmosphere!!!
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Solar Eclipses
Moon 400 X smaller than the Sun, but 400X closer
The moon subtends the same angle as the Sun!
Solar eclipses occur when the moon crosses the
orbital plane of the Earth and when it is
between the Earth and the Sun this happens
during New Moon!!!
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Solar eclipses
Diamond Ring Effect
Total Eclipse
Never look directly into the Sun during an
eclipse unless you have a special solar filter
or during totality!!!