Transcript constellations - Otterbein University

Patterns in the Sky & Constellations
WebAssign, etc.
• Course Homepage:
http://faculty.otterbein.edu/UTrittmann/IS24
03-02/index.htm
• Username: first initial plus last name, no
space
– Uwe Trittmann  utrittmann
• HW #1 due Friday 8pm
Review Sun’s Shadow and
Position
• Tangent = ratio of 2 sides of triangle
• Sun is never overhead in Westerville
What is Astronomy?
• The science dealing with all the celestial bodies in
the Universe
– Cosmology is the branch of astronomy that deals with
the cosmos, or Universe as a whole
• The medieval list of the Liberal Arts: grammar,
rhetoric, logic (trivium); arithmetic, music,
geometry and astronomy (quadrivium)
• Is an “exact science” for ~5000 yrs
– Most rapid advancements in astronomy have occurred
during the Renaissance and the 20th century
– Success has been a result of development and
exploitation of the scientific
method
Astronomy and Culture
• Astronomy had and has an enormous
influence on human culture and the way we
organize our lives
• For example:
– The year is the rotation period of the Earth
around the Sun
– The year is subdivided into months, the period
of the Moon around the Earth
– The weeks seven days are named after the
seven bodies in the solar system known in
antiquity: Sunday, Monday, Saturday (obv.),
Tuesday=Mardi, Wednesday = Mercredi,
Thursday=Jeudi, Friday=Vendredi
Our vantage point: Earth
Basic Observations in Astronomy
• We see (on clear days!):
– A very bright disk that is up about 12 hours. It comes up in
a specific direction, rises higher until it reaches a maximal
altitude in a second direction, then sinks lower until
disappearing in a direction opposite of the direction where
is came up
– A less bright object that changes its appearance and is also
up for a (different) duration of 12 hours. Same rise/set
pattern as very bright object.
– When the very bright disk is not visible, we see many tiny
specs of light of different brightness and color
Basic Observations in Astronomy
• We see further:
– The tiny specs move across the sky as the hours go by. One
group moves across the sky in 12 hours. Same rise/set
pattern as bright object.
– The position of the specs wrt other specs is fixed, but they
move wrt to the ground
– Careful observation reveals a handful of exceptions from
this rule:
• some bright specs move slowly wrt to the other fixed specs, and also
are visible 12 hours. Same rise/set pattern as bright object.
• One spec sits at the center of this motion and does not move
Conventions
• These patterns repeat every day, let’s name
them
–
–
–
–
–
–
Sun
East, South, West
Moon
Daytime + Nighttime = Day (needs to be revisited later!)
Planets
Polaris, the North Star
More names, now that we’ve seen
Observer
Coordinates
• Horizon – the
plane you stand on
• Zenith – the point
right above you
• Meridian – the
line from North to
Zenith to south
Hypothesis
• During a day, it looks like all “lights in the
sky” travel around us, like the are fixed to
an (invisible) sphere that turns around us.
• Call it The Celestial Sphere
Further Observation
• If we move to a new observing place on
Earth, the pattern remains the same (bright
light rises & sets, etc.), but:
– Position of North Star changes
– Maximal altitude of Sun, special stars changes
Conclusion: Earth’s coordinates
projected onto Sky
The Celestial Sphere
• An imaginary sphere
surrounding the earth,
on which we picture the
stars attached
• Axis through earth’s
north and south pole
goes through celestial
north and south pole
• Earth’s equator 
Celestial equator
Celestial Coordinates
Earth: latitude, longitude
Sky:
• declination (dec)
[from equator,+/-90°]
• right ascension (RA)
[from vernal equinox,
0-24h; 6h=90°]
Examples:
• Westerville, OH
40.1°N, 88°W
• Betelgeuse (α Orionis)
dec = 7° 24’
RA = 5h 52m
Confusing! Let’s go with Patterns
in the Sky!
• We can group specs of light together to form
triangles, squares, etc.
• This allows us to find them the next night and
follow their motion
• Talk to other observers, and give them
names: Bear, Bull, Lion, Hunter, Queen, etc.
 The Constellations
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)
Constellation 1: Orion
Orion as seen at night
Orion as imagined by men
Orion “from the side”
Stars in a constellation are not connected in
any real way; they aren’t even close
together!
Constellation 1: Orion
• “the Hunter”
• Bright Stars:
D) Betelgeuze
E) Rigel
• Deep Sky Object:
i) Orion Nebula
Constellation: Gemini
• “the Twins”
• zodiacal sign
• Brightest Stars:
I) Castor
J=K) Pollux
Define Noon
• I.e. agree on the word “noon” meaning
(being equivalent to) “time when the sun
reaches the highest altitude in the observer’s
sky”
• Note that this time is
– different when you are further east or west
– the same when you are further north or south
• Note that the sun culminates in the North in
the southern hemisphere!
Define South
• Either opposite of direction to the North
Star
• Or: direction in which the sun culminates
Why are Polaris and the Sun in
opposite directions?
• They are not exactly, because “the north
direction” and “the south direction” do not
exist
• Their positions are related because
– the direction of Polaris defines the rotation axis
of the celestial sphere
– The sun is somewhere on the sphere
– From a “skewed” perspective everything on the
sphere culminates on the meridian
Reminder: Observer Coordinates
• Horizon – the
plane you stand on
• Zenith – the point
right above you
• Meridian – the
line from North to
Zenith to south
What you see depends on where you are!
• Your local sky –
your view depends on your location on earth
Look
North in
Westerville
Look
North on
Hawai’i
Pete at the Pole
You’re stranded on a desert island. You
locate the pole star. It is 17 degrees above
the northern horizon. What is your latitude?
•
•
•
•
73 degrees south
17 degrees north
Depends on the time of the day
Depends on the time in the year
Activity: Angles
• See also iSkylab Manual, Moon Option
Sun Measurement - 01
• We measured at 11:30 am on Jan 29, 2014
• Length of the shadow of a meter stick was
1.72m
• Trigonometry: 30.2 degrees (sig figs!)
Sun Measurement - 02
• We measured at 2:00 pm on Jan 29, 2014
• Length of the shadow of a meter stick was
1.69m
• Trigonometry: 30.6 degrees (sig figs!)
Is this good or bad or what?
• Compare to expected value:
– Westerville location 40° N latitude
– Celestial equator 90° off of that
• “that” being North AND 40° above horizon
– Sun’s celestial (not observer!) coordinates on
January 29: -18°, i.e. south of Celestial Equator
(see YourSky)
– So: 40° + 90 °+18 ° = 148° above N horizon
= 32° above S horizon