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Ancient astronomy & celestial sphere ASTR 1010 Lecture 3.

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Ancient astronomy & celestial sphere ASTR 1010 Lecture 3
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Page 1: Ancient astronomy & celestial sphere ASTR 1010 Lecture 3.

Ancient astronomy & celestial sphere

ASTR 1010

Lecture 3

Page 2: Ancient astronomy & celestial sphere ASTR 1010 Lecture 3.

In this lecture, you will learn2-1 The importance of astronomy in ancient civilizations around

the world

2-2 That regions of the sky are divided around groups of stars called constellations

2-3 How the sky changes from night to night

2-4 How astronomers locate objects in the sky

Page 3: Ancient astronomy & celestial sphere ASTR 1010 Lecture 3.

Naked-eye astronomy

Although physical properties of celestial objects cannot be obtained from naked-eye astronomy, questions like

• why are there seasons?• why the night sky changes over

time?• why the night sky looks different at

different places on Earth?

can be addressed and studied with our bare eyes.

Page 4: Ancient astronomy & celestial sphere ASTR 1010 Lecture 3.

Ancient positional astronomy

Positional astronomy : the study of the positions of objects in the sky.

Stonehenge – ancient British Sun Dagger – ancestral Puebloans Machu Picchu Egyptian pyramids (3000BC) tomb of Shih Huang Ti (~250BC)

Mayan Astronomy : Could measure the period of Venus (584 days versus 583.92 days)!

Venus being associated with wars, and need to predict the best dates for attack.

Lead into the divisions of the night sky into constellations.

Sun Dagger at Chaco Canyon : a band of light strikes the center of the spiral on the first day of summer (about 1000AD)

Page 5: Ancient astronomy & celestial sphere ASTR 1010 Lecture 3.

Constellations On a clear night, with 20/20 vision, one can see about 3,000 stars at a given time. Ancient astronomers traced out “pictures” using groups of these stars. “Group of

Stars” in Latin constellations

Page 6: Ancient astronomy & celestial sphere ASTR 1010 Lecture 3.

Constellations International Astronomy Union (IAU) divided the entire night sky into 88

constellations. Helpers to find a way around the sky. Connection to the ancient astronomy, and good tool to naming stars (e.g., alpha

Orioni the brightest star in Orion) stars in a constellation only appear to be close in the projected sky. In reality, most

of these stars are not related each other (not even close in 3D).

Page 7: Ancient astronomy & celestial sphere ASTR 1010 Lecture 3.

Diurnal Motion = daily motion of celestial objects At any moment, half of

Earth is illuminated by the Sun day-side and night-side.

Seen from North Pole, Earth rotates from West to East making one complete rotation in 24 hours. for a person on Earth, the sky appears to rotate from east to west

“west to east” rotation is not a good expression. Seen from the North Pole, Earth rotates counter-clockwise!

Page 8: Ancient astronomy & celestial sphere ASTR 1010 Lecture 3.

Diurnal Motion (animation) Stars do not move!

We are the one that move!

This image…o day in Asiao America &

Europe = night

For a person in California, Cygnus is directly overhead

Page 9: Ancient astronomy & celestial sphere ASTR 1010 Lecture 3.

Diurnal Motion (animation) 4 hours later…

since Earth rotated 60 degrees, now a different constellation (Andromeda) is directly overhead now.

Page 10: Ancient astronomy & celestial sphere ASTR 1010 Lecture 3.

Yearly Motion As Earth orbits around the Sun, the nighttime

side of the Earth gradually turns toward different parts of the sky. Hence, the particular stars that you see in the night sky are different at different times of the year.

Winter constellation = Orion Spring constellation = ? Summer constellation = Autumn constellation = ?

Page 11: Ancient astronomy & celestial sphere ASTR 1010 Lecture 3.

North Star and Big Dipper

Page 12: Ancient astronomy & celestial sphere ASTR 1010 Lecture 3.

Winter Triangle

Page 13: Ancient astronomy & celestial sphere ASTR 1010 Lecture 3.

Summer Triangle

Try…

Stellarium

stellarium.org

Free planetariumsoftware

Page 14: Ancient astronomy & celestial sphere ASTR 1010 Lecture 3.

Ancient people believed that all stars are at the same distance from Earth and they are “attached” to the hollow sphere called “celestial sphere” and this celestial sphere rotates once a day.

In truth, the diurnal motion is due to the Earth rotation.

Visible stars to naked-eye range from 4.2 Ly to ~1,000 Ly.

Celestial sphere is an imaginary sphere in the sky which has an infinite radius.

celestial polescelestial equator

Celestial Sphere

Page 15: Ancient astronomy & celestial sphere ASTR 1010 Lecture 3.

Ancient people believed that all stars are at the same distance from Earth and they are “attached” to the hollow sphere called “celestial sphere” and this celestial sphere rotates once a day.

In truth, the diurnal motion is due to the Earth rotation.

Visible stars to naked-eye range from 4.2 Ly to ~1,000 Ly.

Celestial sphere is an imaginary sphere in the sky which has an infinite radius.

celestial polescelestial equatorzenithhorizon

Celestial Sphere

Page 16: Ancient astronomy & celestial sphere ASTR 1010 Lecture 3.

For an observer at the northern hemisphere…

stars sufficiently close to the the celestial north pole never set (i.e., always stay above the horizon). These stars are known as circumpolar stars.

Some stars sufficiently close to the celestial south pole will never rise above the horizon.

Apparent motion of stars can tell use about the latitudes of the observer (and the direction of the observation).

Motions of the Celestial Sphere

Page 17: Ancient astronomy & celestial sphere ASTR 1010 Lecture 3.

Mid-latitude, looking North

Apparent motion of Stars

Page 18: Ancient astronomy & celestial sphere ASTR 1010 Lecture 3.

mid-latitude looking south

Star trails…

Star trails over the Gemini Northern Telescope dome. The glow from the eruption of the Kilauea volcano is seen on the left. The trail of a meteor is visible in this photograph.

Page 19: Ancient astronomy & celestial sphere ASTR 1010 Lecture 3.

Star trails…

Page 20: Ancient astronomy & celestial sphere ASTR 1010 Lecture 3.

Star tails at middle northern latitudes

Looking West Looking East

Page 21: Ancient astronomy & celestial sphere ASTR 1010 Lecture 3.

In summary…

Important ConceptsAncient positional astronomyConstellationCelestial SphereDiurnal MotionSeasonal starsStar trails

Important TermsCelestial sphereCelestial North PoleCelestial South PoleCelestial EquatorHorizonZenith

Chapter/sections covered in this lecture : sections 1.1, 1.2, 1.4, 2.1, 2.3


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