Chapter E Exploring The Heavens

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Chapter EExploring The Heavens

• AST1002 Introduction to Astronomy
• Dr. Mike Reynolds

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What is Astronomy?

• Astronomy, simply stated, is the study of the
  Universe.
• Astronomers classify objects into numerous groups
• Some of these groupings like stars are easy
  to understand scientifically
• Others are more difficult

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Basic Objects in the Universe

• Stars glowing balls of gas that undergo nuclear
  fusion
• Planets moderately-large objects orbiting a star
• May be rocky or gaseous
• Visible due to reflecting light
• What is the size to be a planet?
• Usually somewhat spherical, regular-shaped
• Satellite orbits a planet four major groups
• Also called a moon
• Earths satellite Moon (proper noun)

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Basic Objects in the Universe

• Asteroid relatively small, rocky/metallic object
  usually orbiting a star
• Comet relatively small, icy object usually
  orbiting a star
• Solar System Sun and all the objects which orbit
  the Sun, including the planets
• Star or Stellar System A star and other objects
  such as planets and/or other stars and other
  materials that orbit it

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Basic Objects in the Universe

• Moving beyond our Solar System
• Galaxy large island of stars
• Few hundred million to over a trillion stars!
• Galactic Cluster collection of galaxies
  gravitationally bound
• Supercluster region where galaxies and galactic
  clusters are tightly packed
• Universe all matter and energy
• Also called the Cosmos

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Some Questions To Ponder

• Can a planet become a star?
• Can a planet be declassified as a planet?
• Can a moon become a planet? Or a planet a moon?
• Does a galaxy have to have stars with planets to
  be a galaxy?

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Scale of the Cosmos

• BIG!!!
• Start with Our Solar System
• Earth-Moon distance mean 230,000 miles
• Earth-Sun distance mean 93,000,000 miles
• 1 Astronomical Unit or 1 AU 93,000,000 miles
• The Suns diameter is about 850,000 miles
• The Earths diameter is just under 8,000 miles
• Imagine if the Sun was an Orange

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Motion

• Terms you have heard or will hear
• Rotation the spinning of an object around its
  axis
• Earth rotates once every 24 hours (approx.)
• Jupiter rotates once every 10 hours (approx.)
• Revolution One object orbiting a second
• Earth revolves around the Sun every 365.24 Earth
  Days approx. 1 year
• Jupiter revolves around the Sun every 11.86 Earth
  Years approx. 1 Jovian year

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The Constellations

• Early peoples told stories about the shapes they
  saw in the stars
• These shapes are called Constellations
• Today astronomers recognize 88 official
  Constellations
• Some Constellations are easy to recognize
• Most are not!
• We cannot see all 88 constellations from here we
  would need to be at the equator

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Constellations Over the Centuries

• Many peoples identified patterns in the stars
• One example Orion the Hunter, the official
  Constellation
• China Shen, supreme warrior
• India/Hindus Skanda, celestial general riding a
  peacock
• Egypt Osiris
• Most of todays 88 official constellations are
  Western European in design

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Other Patterns

• Asterism Star pattern within a Constellation
• Not an official Constellation
• The Big and Little Dippers
• within Ursa Major and Ursa Minor
• Pleiades within Taurus
• The Seven Sisters
• Japanese Subaru
• Navajo Dilyehe
• Hawaiian Makahiki or many little eyes

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Our Night Skies

• Celestial Sphere an imaginary sphere on which
  all the objects in the sky appear to lie when
  observed from a specific place
• This sphere appears to surround the Earth
• The Celestial Sphere appears to move
• The Sun and Moon (as well as the bright planets)
  also appear on the Celestial Sphere, moving
  independently

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Divisions in the Celestial Sphere

• North and South Celestial Poles the points at
  which the Celestial Sphere appears to turn/rotate
• An extension of Earths axis
• Stars rotate about these points
• Pole Shorthand
• North Celestial Pole NCP
• South Celestial Pole SCP

Polaris
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What Points Do We SeeLooking Up?

• Local Sky sky we see from where we stand
• Ecliptic Suns annual path across the Celestial
  Sphere
• Why is the Ecliptic not on the Celestial Equator?
• Zenith point directly overhead
• Meridian imaginary line from due north to the
  zenith to due south
• The Meridian divides the sky into halves

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Other Moving Objects

• The Sun
• Ecliptic path
• Constellations along Ecliptic historically 12
  but officially 13 are called the Zodiac
• When the Sun is in Leo will the stars
  surrounding Leo be visible?
• The Moon
• Also travels along the Ecliptic
• Sometimes in the evening sky, sometimes in the
  morning, sometimes not visible at all

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Measuring the Sky
How the Sun and Moon Appear to Us in the Sky

• Astronomers use Degrees, Minutes and Seconds to
  measure distances across the sky or sizes
• Referred to as Angular Sizes the angle the
  object appears to span or distance between
  objects
• Sun and Moon appear to be about ½ degree
• Not their true sizes just how they appear to us
• 60 arcseconds 1 arcminute
• 60 arcminutes 1 degree

½ degree 30 arcminutes
½ degree 30 arcminutes
But in the Real Universe the Sun is 400 times
bigger than the Moon!
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Seasonal Changes

• Seasons occur on a planet or moon because the
  axis of rotation remains tilted in one direction
  during its orbit
• The tilt is relative to the planets or moons
  orbit
• This tilt results in a planet or moon having
  Seasons
• Earths axis is tilted about 23 ½ degrees
• Uranus axis is tilted about 98 degrees

Orbital Plane
Earth 23 ½o tilt
Uranus 98o tilt
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Seasons on Earth

• Nothing to do with the distance to the Sun
• Summer in the Northern Hemisphere
• Winter in the Southern Hemisphere
• Winter in the Northern Hemisphere
• Summer in the Southern Hemisphere
• Sun angles in the Summer and Winter make for
  differences in temperature

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Seasonal Terms

• Summer Solstice Suns rays are most-direct
• Winter Solstice Suns rays are least-direct
• Spring or Vernal Equinox Equal day and night,
  going from shorter to longer days
• Fall or Autumnal Equinox Equal day and night,
  going from longer to shorter days

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Some Other Seasonal Stuff

• At the Equinoxes, the Sun rises due east and sets
  due west only at the Equinoxes
• Noan egg will not stand on end because its the
  1st day of Spring (or Fall)
• Summer the day is longer, the night shorter
• Extreme at far latitudes midnight Sun
• Winter the day is shorter, the night longer
• Extreme at far latitudes no Sun!

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Will Seasons Always be the Same?

• No! Orientation of Earths axis changes
• Precession the circular motion of a planets
  tilted axis
• Slow process Earth 26,000 years to complete
  one precession
• What are the effects of precession?
• Celestial poles change
• Timing of Seasons change
• Nutation A wobble in the wobble!

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The Moon in Our Sky

• It takes 27 1/3 days for the Moon to go around
  Earth one time
• From new Moon to the next new Moon takes 29 ½
  days.
• Moonth month!
• Why? Earth has also moved through space and the
  Moon has to catch up with that starting position.
• Roughly the same side of the Moon faces Earth
• 1 lunar rotation 1 lunar revolution
• One half of the Moon is always illuminated by the
  Sun

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The Phases of the Moon

• We see the Moon go through its phases due to the
  position of Earth-Moon-Sun relative to each other
• NOT
• Clouds
• Moon moves closer or the Sun further away
• Little Green Men aliens

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Moon Phase Terminology

• Crescent Moon less than 50 illuminated
• Gibbous Moon more than 50 but less than 100
• Waxing Growing larger
• New Moon up to Full Moon
• Waning Growing smaller
• Right past Full Moon to New Moon
• Full Moon 100 illuminated
• New Moon 0 illuminated no Moon

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More Moon

• Can you see the Moon in the daytime?
• Yes!
• Does the Moon keep a constant distance from
  Earth?
• No, varies from a Perigee of about 225,000 miles
  to an Apogee of about 243,000 miles
• Perigee? Apogee? Refers to the Moons closest and
  farthest distances

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Lunar Eclipses

• A Lunar Eclipse occurs when Earth lies directly
  between the Sun and the Moon, so that Earths
  shadow falls on the Moon
• Three types
• Penumbral
• Partial
• Total
• Entire night side of Earth can see the eclipse
• Total lunar eclipses can vary in color and
  brightness due to Earths atmosphere
• Red to Copper to Orange to Black!

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July 1982 Total Lunar Eclipse trail Photograph
by Jay Anderson
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Solar Eclipses

• Four Types
• Partial
• Annular or Ring Eclipse
• Annulars are like a type of partial
• Total
• Total-Annular or Hybrid
• Must be within the eclipse zone to see even a
  partial solar eclipse

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Annular Sequence Photos 10 May 1994
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Total Solar Eclipses

• Moon totally blocks all harmful solar light and
  radiation at totality (not during partial)
• Daytime becomes nighttime
• Moons shadow, sunrise/sunset effect
• Animal reactions
• Several events and solar features visible
• Bailys Beads
• Diamond Ring
• Corona
• Prominences

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Total Solar Eclipses simply the most-spectacular
astronomical event (in my humble opinion)
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Total Solar Eclipses

• Others have been profoundly affected by a total
  solar eclipse
• St. Benedict
• A total solar eclipse so impacted him that he
  started his still-famous work the Benedictine
  Society

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