Download Astro 1 ppt - Red Hook Central Schools

Astronomy
Contents of the universe
We live in the solar system.
Earth orbits the sun every yr in
elliptical orbit.
Distance Earth to sun 1 AU
Birth of the Solar System
Solar system born ~4.5 BYA
2 min
http://www.youtube.com/watch?v=
qfdDWdZcpOw
Our Solar System
planets/moons/asteriods
Asteroid Belt mars-Jupiter
Icy Comets
-All orbit the sun
-very elliptical orbits
Solar system is part of the
milky way galaxy. Orion Arm.
The galaxy revolves around
black hole. Sun revolution ~ 250
million y.
Galaxies –large aggregates of stars, gas,
& dust containing ~ 100 billion (1011)
stars ranging in diameter from 1,500 to
300,000 light-years across. Orbit central
point. Av distance btw stars 10 ly.
Stars can form stellar clusters w/i
galaxies – smaller groups of stars held
by gravity. ~ 1000’s of stars.
Constellations – star groups not
necessarily near each other.
Galaxies form groups too.
Galactic Clusters
• Nearest cluster = Virgo cluster
Open Cluster
• also galactic cluster- a group of up to a
few thousand stars that were formed
from the same giant molecular cloud
and have roughly the same age. Contain
gas and dust
Globular Cluster - older
• Generally outside Milky Way in Halo.
Nebulae
• Gas clouds – Star nurseries
• Formed after Big Bang
• from supernova
It’s a long way btw stars.
Use Light Years LY
The d light travels in 1 yr.
• 1 LY = 9.46 x 10 15 m.
• 1 AU = 1.5 x 10 11m
• 1 pc parsec = 3.09 x 1016 m
Powers of 10 Film 6:30 min
http://www.youtube.com/watch?v=tnhken4_-A0
Earth’s Rotation makes
stars appear to rotate on
fixed sphere.
Rotation is around Polaris on
24 h cycle.
Sun/planets wander through
stellar backdrop.
From Earth Stars Appear to be
embedded in sphere.
Stars rotate around Polaris
24 hr cycle rise east set west
Stars appear fixed on sphere relative to
each other.
http://www.youtube.com/watch?v=JCr_Pz4h2Bw
Planetary Motion Wanderer &
Retrograde
• Know the planets in order, their relative
sizes, the asteroids, Kuiper belt.
• Clusters, galaxies, nebula
Measuring Stellar Distances
• Stellar Parallax few hundred pc
• Absolute & Apparent Magnitudes
• Spectroscopic Parallax
• Cepheid variables
distance
Stellar Parallax
• Hold up pencil
• Blink eyes
• Pencil moves against backdrop.
• Look at post.
• Blink eyes.
Earth’s motion in orbit causes parallax.
1 AU
Sun
Measure Parallax Angle
• Angles are very small – measured in arc seconds.
Angular Measurements
• expressed in degrees, arc-minutes
or arc-seconds.
• 360o in circle
• 1° = 60 arc minutes.
• 1 arcminute = 60 arc sec.
• 1 pc= distance where an object has
a parallax angle (p) of one arc
second.
Stellar Parallax
d = 1/p
p = 1/d
d (dist) – #parsecs
p (parallax angle) – #arc-seconds.
Ex 1: The nearest star to Earth is Alpha Centauri,
which is at a distance of 4.37 ly. Calculate the
parallax angle that was measured to obtain
that distance.
• 4.37 LY / 3.26 = 1.34 pc.
• p = 1/d
• 0.746 arc-sec
1/1.34 pc
Ex 2: A star has a parallax of 0.66 arc sec.
A. What is this in parsecs?
B. Meters?
• d = 1/p
• d = 1/ 0.66 = 1.5 pc.
• 4.63 x 1016 m.
Why can’t stellar parallax be used to
measure very distant stars?
• Angle gets too small. Few hundred pc
upper limit.
Parallax Method Clip 11 min
• https://www.youtube.com/watch?v=XUQAI
ldqPww