Patterns in the Sky & Constellations

Daily Homework & Warm-Ups

• Before class (8am): answer warm-up

questions online about reading for the day

– http://neutrino.otterbein.edu/~tagg/Courses/Too

ls/WarmupDB/Astronomy_Section_1

• After Class: use WebAssign, an online

homework system daily!

– Password & username: first initial plus last

name all lowercase, e.g. utrittmann

• Course Homepage from my homepage

Some of Today’s Warm-Up Answers

• What is a constellation?

– S. One: A constellation is a pattern formed by a

collection of stars. Most often they are named

after the shape they make up or a figure in

Greek mythology.

• Why is the Celestial North Pole directly

"above" the earth's (geographic) north pole?

– Thad Guy: The celestial north pole is an

extension of the Earth's geographic north pole

and therefore always lies directly above it.

Peer Instruction: How it works

• Peer instruction is learning by instructing your fellow students and being instructed by them

• The process involves 6 steps:

– Mini-lecture by course instructor

– Conceptual multiple-choice question is put up

– Flash-cards are used to “poll the audience”

– A few minutes of discussion between students

– “Final answer” via flash-cards

– The instructor explains the correct answer

Who was the first man on the

Moon?

• Yuri Gagarin

• Buzz Aldrin

• Neil Armstrong

• John Glenn

Concept Questions

• Concept questions maybe easy to answer, but are not simple

• You need background knowledge to answer them

• They teach you how to use facts and knowledge to find the answer to a problem

• They test if you got the concept rather than just knowing facts

It is New Moon. In one week, what

will the phase of the Moon be?

• New Moon

• First Quarter Moon

• Full Moon

• Last Quarter Moon

Why it works • Carefully chosen questions

• It is easier to be convinced and to convince

if the reasoning is sound and hence the

answer correct

1

2

3

4

5

Right to right

Wrong to right

Right to wrong

No 2nd answer

wrong to wrong

How

answers are

revised in a

typical

question

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

Why study Astronomy?

• Practical reasons: seasons, tides, navigation, space technology, satellite communication

• Idealistic reasons: cosmological questions (“Where do we come from?”), aesthetics, curiosity

“Two things fill the mind with ever new and increasing

admiration and reverence, the more frequently and enduringly the reasoning mind is occupied with them: the star spangled sky over me and the moral law in me.” (I. Kant)

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