stars and star names. 88 official constellations
TRANSCRIPT
Stars and star names
88 official constellations
α alpha i iota ρ rhoβ beta κ kappa σ sigmaγ gamma λ lambda τ tauδ delta μ mu υ upsilonε epsilon ν nu φ phiζ zeta ξ xi χ chiη eta ο omicron ψ psiθ theta π pi ω omega
Constellation PossessiveAries ArietisTaurus TauriGemini GeminorumCancer CancriLeo LeonisVirgo VirginisLibra LibraeScorpius ScorpiiSagittarius SagittariiCapricornus CapricorniiAquarius AquariiPisces Piscium
Betelgeuse = a - Orionis = HIP 27989 = etc….
Mintaka = d - Orionis = HIP 29530 = etc…..
Objects move daily across the sky. Why?
North pole
(Right hand rule)
Because we live on a ball that’s spinning!
Because we live on a ball that’s spinning:
N
up
E
W Rise in the East
because we live on a ball that’s spinning:
up
N
E
N
up
N
E
W
Sets in the West
So, everything appears to move from east to west.(On a daily basis)
Two kinds of day!
Solar day: The time it takes the earth to rotate once with respect to the sun.
Trouble: The solar day changes with the time of the year!
Mean Solar day: The average of the solar day over a year.
Our clocks measure mean solar time (MST):
1 hour = 1/24th of a mean solar day 1 min = 1/60th of an hour 1 sec = 1/60th of a min
Sidereal Day: time between a star’s meridian crossings
1 sidereal day = 23 hr 56 min and 4.091 sec (MST)
If the sidereal day is constant, why not use it to calibrate our
watches?
sidereal day also divided up into hour, minutes, sec (sidereal)
The Celestial Sphere
We can think of all these stars as fixed on a big celestial sphere
C.S. fixed
Earth spinstowards East
OR …
We can think of all these stars as fixed on a big celestial sphere
Earth fixed
C.S. spinstowards West
What we see from our specific locale
The natural (local) way:
Apparent S Horizon
Apparent N Horizon
Zenith
N pole S pole
Apparent horizons depend on your
height, mtns etc …
The natural (local) way:
Zenith
N pole S pole
‘True’ (local) horizon
celestial N pole
celestial S pole
celestialequator
celestial sphere rotates
Polaris
celestial N pole
celestial S pole
celestialequator
local horizon
zenith
Earth’sequator
latitude
celestial N pole
celestial S pole
celestialequator
local horizon
Make Earth very small (Since everything is so far
away!)
zenith
latitude
Polaris
latitude
local horizon
celestial N pole
celestial S pole
celestialequator
local horizon
celestial sphere rotates (instead of the earth)
Motions of the stars relative to the fixed earth!
celestial N pole
celestial S pole
celestialequator
local horizon
zenith
Blue area is below observer’s horizon
celestial N pole
celestial S pole
celestialequator
local horizon
zenith
celestial N pole
celestial S pole
celestialequator
local horizon
zenith
celestial N pole
celestial S pole
celestialequator
local horizon
zenith
celestial N pole
celestial S pole
celestialequator
local horizon
zenith
celestial N pole
celestial S pole
celestialequator
local horizon
zenith
celestial N pole
celestial S pole
celestialequator
local horizon
zenith
celestial N pole
celestial S pole
celestialequator
local horizon
Circumpolar!
celestial N pole
celestial S pole
local horizon: observer at earth’s equator
Observer’s zenith
No circumpolar
celestial N pole
celestial S pole
local horizon: observer at 45˚ N
Observer’s zenith
celestial N pole
celestial S pole
local horizon: observer N pole
zenith
All circumpolar
Putting the sun’s position on the celestial sphere
(The ecliptic)
Earth’s tilted by 23 ½ °
Sun’s daily motion
Sun’s yearly motion on celestial sphere
The seasons
Earth’s tilted by 23 ½ °
Relative to the plane of its orbit around the sun
Axis always points in the same direction (celestial N pole)
celestial N pole
(N) summer solstice≈ June 21
celestial N pole
Equinox:
(N) Autumn (Autumnal) ≈ September 22
(N) Spring (Vernal)≈ March 21
celestial N pole
(N) winter solstice≈ December 21
Why is winter cold and summer hot?
“Precession of the equinox”
The Earth isn’t a perfect sphere!Non-zero torque from sun and moon!
Spinning objects subjected to a torque precess!
Precession of the North celestial pole.