Basic Observations in Astronomy

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Basic Observations in Astronomy
Welcome to

• Classes without Quizzes
• -Alumni Weekend at Otterbein-
• June 8-10, 2007
• Dr. Uwe Trittmann

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Basic Astronomy

• Possible topics
• Basic observations
• Star Maps
• Telescopes
• The Night Sky in June
• Eclipses

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Basic Observations in Astronomy

• Positions of objects (sun, moon, planets, stars
  )
• Motion of objects
• with respect to you, the observer
• - with respect to other objects in the sky
• Changes (day/night, seasons, etc.)
• Appearance of objects (phases of the moon, etc.)
• Special events (eclipses, transitions, etc.)
• ? All in the sky, i.e. on the Celestial Sphere

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Whats up in the night sky?

• The Celestial Sphere
• An imaginary sphere surrounding the earth, on
  which we picture the stars attached
• Axis through earths north and south pole goes
  through celestial north and south pole
• Earths equator
• Celestial equator

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Celestial Coordinates

• Earth latitude, longitude
• Sky
• declination (dec) from equator,/-90
• right ascension (RA) from vernal equinox, 0-24h
  6h90
• Examples
• Westerville, OH 40.1N, 83W
• Betelgeuse (a Orionis) dec 7 24
  RA 5h 52m

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Whats up for you?

• Observer Coordinates
• Horizon the plane you stand on
• Zenith the point right above you
• Meridian the line from North to Zenith to south

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depends where you are!

• Your local sky
• your view depends on your location on
  earth

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Look North in Westerville
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Look North on Hawaii
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Daily Rising and Setting

• Due to the rotation of the Earth around its axis
• Period of rotation 1 siderial day
  23h56m4.1s
• 1 solar day (Noon to Noon) 24h
• Stars rotate around the North Star Polaris

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Solar vs Siderial Day

• Earth rotates in 23h56m
• also rotates around sun
• ? needs 4 min. to catch up
• Consequence stars rise 4 minutes earlier each
  night
• after 1/2 year completely different sky at night!

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Another Complication Axis Tilt!

• The Earths rotation axis is tilted 23½ degrees
  with respect to the plane of its orbit around the
  sun (the ecliptic)
• It is fixed in space ? sometimes we look down
  onto the ecliptic, sometimes up to it

Rotation axis
Path around sun
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Position of Ecliptic on the Celestial Sphere

• Earth axis is tilted w.r.t. ecliptic by 23 ½
  degrees
• Equivalent ecliptic is tilted by 23 ½ degrees
  w.r.t. equator!
• ? Sun appears to be sometime above (e.g. summer
  solstice), sometimes below, and sometimes on the
  celestial equator

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The Seasons

• Change of seasons is a result of the tilt of the
  Earths rotation axis with respect to the plane
  of the ecliptic
• Sun, moon, planets run along the ecliptic

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The Zodiac throughout the Year

• Example In Winter sun in Sagittarius, Gemini at
  night sky in summer sun in Gemini, Sagittarius
  at night sky

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Constellations of Stars

• About 5000 stars visible with naked eye
• About 3500 of them from the northern hemisphere
• Stars that appear to be close are grouped
  together into constellations since antiquity
• Officially 88 constellations
  (with strict boundaries for
  classification of objects)
• Names range from mythological (Perseus,
  Cassiopeia) to technical (Air Pump, Compass)

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Constellations of Stars (contd)

• Orion as seen at night Orion as
  imagined by men

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Constellations (contd)

• Orion from the side
• ?Stars in a constellation are not connected in
  any real way they arent even close together!

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Understanding and using Star Maps

• The night sky appears to us as the inside of a
  sphere which rotates
• Problem find a map of this curved surface onto a
  plane sheet of paper
• Lets explore our turning star map!

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Fixed and unfixed Stuff

• The stars are fixed to the rotating sky globe
• ?They move from East to West and also from near
  to the horizon to higher up in the sky
• The Solar System bodies (Sun, Moon, Planets,
  Asteroids, Comets) move with respect to the fixed
  stars
• SSBs have complicated paths their own motion is
  added to the overall motion of the celestial
  sphere

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Motion of Sun, Moon and other Planets

• All major bodies in the Solar System move around
  ecliptic
• Slow drift (from W to E) against the background
  of stars

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Reason All planets move in same plane!
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Motion of the Moon

• Moon shines not by its own light but by reflected
  light of Sun
• ? Origin of the phases of the moon
• Moon revolves around the Earth
• period of revolution 1 month

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Phases of the Moon
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Phases of the Moon (contd)

• Moon rotates around earth in one month
• Moon rotates around itself in the same time
• ? always shows us the same side!
• ? dark side of the moon (not dark at all!)

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Motion of the Planets

• Along the ecliptic as Sun and Moon
• But exhibit weird, retrograde motion at times

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Strange motion of the Planets

• Planets usually move from W to E relative to
  the stars, but sometimes strangely turn around in
  a loop, the so called retrograde motion.
  

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The heliocentric Explanation of retrograde
planetary motion

• See also SkyGazer

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SkyGazer

• A computer program that simulates the vision of
  the sky during day and night
• Things to observe
• Set your position on Earth observe how view of
  sky changes as you move E,W, N,S
• Note the distribution of sunlight on Earth!
• Rotation is around Polaris which is not in zenith

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SkyGazer

• Things to observe (contd)
• Sun, moon, planets, stars rise (E) and set (W)
• In the southern hemisphere the sun is highest in
  the north
• Planets sometimes move backward
• Moon phases
• Planets have phases, too!

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Telescopes

• Light collectors
• Two types
• Reflectors
• (Mirrors)
• Refractors (Lenses)

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Refraction

• Lenses use refraction to focus light to a single
  spot

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Reflection

• Light that hits a mirror is reflected at the same
  angle it was incident from
• Proper design of a mirror (the shape of a
  parabola) can focus all rays incident on the
  mirror to a single place

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Newtonian Telescope

• Long tubes (approx. focal length)
• Open at front
• Eyepiece on side

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Schmidt-Cassegrain Telescope (CAT)

• Very compact easy to use
• Closed (Corrector plate)
• Resonably priced

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Refractor

• Two lenses -gt inverted image
• Long tube (approx. focal length of objective)
• Usually pretty expensive

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Binoculars

• Erect image -gt good for terrestrial viewing
• Prisms needed to produce erect image
• Typical specs 8x60, means magnifies 8x and
  objective lens is 60 mm in diameter

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A good starting point

• A pair of binoculars and a star map will keep you
  busy for a long time anywhere!
• constellations
• Planets
• Moon
• Orion nebula
• Andromeda Galaxy
• star clusters

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The Night Sky in June

• The sun is at its highest -gt shortest nights!
• Summer constellations are coming up Hercules,
  Scorpius, Ophiuchus (Snake Bearer), Snake
• ? lots of globular star clusters!
• Center of the Milky Way in Sagittarius
• Jupiter, Saturn Venus are easily seen

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Moon Phases

• 6 / 8 (Last Quarter Moon)
• 6 / 14 (New Moon)
• 6 / 22 (First Quarter Moon)
• 6/ 30 (Full Moon)

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Today at Noon

• Sun at meridian, i.e. exactly south

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10 PM
Venus

• Typical observing hour, early June
• no Moon
• Jupiter
• Pluto (experts only)

Saturn
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South-West

• Virgo and
• Coma
• with the Virgo-Coma galaxy cluster

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Virgo-Coma Cluster

• Lots of galaxies within a few degrees

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M87, M88 and M91
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Zenith

• Big Dipper points to the north pole

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South

• Canes Venatici
• Corona Borealis
• Bootes
• Serpens

• Globular Star
• Clusters
• M 3
• M 5
• M 13

• Galaxies
• M 51
• M 101
• M 64 (Bl. Eye)

M 5
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South-East

• Hercules
• Ophiuchus
• Serpens

• Globular Star
• Clusters
• M 13
• M 92
• M 12
• M 10

Summer is Globular Cluster time!
M 5
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M13 Globular Cluster
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South-East

• Ophiuchus
• Serpens
• Scorpius

• Globular Star
• Clusters
• M 4
• M 19
• M 62
• M 80

Summer is Globular Cluster time!
M 5
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Appendix Eclipses
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Eclipses

• One celestial object hidden by other or in the
  shadow of another
• Solar eclipse sun hidden by the moon
• Lunar eclipse moon in earths shadow (sun hidden
  from moon by earth)
• Also eclipses of Jupiters moons, etc.
• Most spectacular because moon and sun appear to
  be the same size from earth

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Solar Eclipses

• Umbra region of total shadow
• Penumbra region of partial shadow
• Totality lasts only a few minutes!
• Why isnt there a solar eclipse every month?

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Solar Eclipse
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Solar Corona
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Question

• Why isnt there an eclipse every month ?
• Answer because the Moons orbit is inclined
  w.r.t. the ecliptic

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Lunar Eclipses

• Moon moves into earths shadow

and out of it (takes hours!)
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Partial Eclipse
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Not an Eclipse !
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Towards Totality
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Almost total
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Totality
Totality