Spaceship Earth How is Earth moving in our solar system? How is our solar system moving in the Milky...
-
Upload
erick-clifford-jefferson -
Category
Documents
-
view
214 -
download
1
Transcript of Spaceship Earth How is Earth moving in our solar system? How is our solar system moving in the Milky...
Spaceship Earth
How is Earth moving in our solar system? How is our solar system moving in the
Milky Way Galaxy? How do galaxies move within the
universe? Are we ever sitting still?
Our goals for learning:
How is Earth moving in our solar system?
Contrary to our perception, we are not “sitting still.”
We are moving with Earth in several ways, and at surprisingly fast speeds.
The Earth rotates around its axis once every day.
Earth orbits the Sun (revolves) once every year:
• at an average distance of 1 AU ≈ 150 million kilometers.• with Earth’s axis tilted by 23.5º (pointing to Polaris)
It rotates in the same direction it orbits, counterclockwise as viewed from above the North Pole.
Our Sun moves randomly relative to the other stars in the local solar neighborhood…
• typical relative speeds of more than 70,000 km/hr• but stars are so far away that we cannot easily notice their motion
… and orbits the galaxy every 230 million years.
How is our Sun moving in in the Milky Way Galaxy?
More detailed study of the Milky Way’s rotation reveals one of the greatest
mysteries in astronomy:
How do galaxies move within the universe?Galaxies are carried along with the expansion of the universe. But how did Hubble figure out that the universe is expanding?
Hubble discovered that:
All galaxies outside our Local Group are moving away from us.
The more distant the galaxy, the faster it is racing away.
Conclusion: We live in an expanding universe.
Are we ever sitting still?
What have we learned? How is Earth moving in our solar
system? It rotates on its axis once a day and
orbits the Sun at a distance of 1 AU = 150 million kilometers.
How is our solar system moving in the Milky Way Galaxy? Stars in the Local Neighborhood move
randomly relative to one another and orbit the center of the Milky Way in about 230 million years.
What have we learned? How do galaxies move within the
universe? All galaxies beyond the Local Group are
moving away from us with expansion of the universe: the more distant they are, the faster they’re moving.
Are we ever sitting still? No! Earth is constantly in motion, even
though we don’t notice it.
Discovering the Universe for Yourself
Patterns in the Night Sky
What does the universe look like from Earth?
Why do stars rise and set? Why do the constellations we see
depend on latitude and time of year?
Our goals for learning:
What does the universe look like from Earth?
With the naked eye, we can see more than 2000 stars as well as the Milky Way.
Constellations
Constellations
A constellation is a region of the sky.
Eighty-eight constellations fill the entire sky.
Constellations
Thought Question
The brightest stars in a constellation:
A. all belong to the same star cluster.
B. all lie at about the same distance from
Earth.
C. may actually be quite far away from each
other.
Thought Question
The brightest stars in a constellation:
A. all belong to the same star cluster.
B. all lie at about the same distance from
Earth.
C. may actually be quite far away from each
other.
The Celestial SphereStars at different distances all appear to lie on the celestial sphere.
The 88 official constellations cover the celestial sphere.
The Celestial Sphere
Ecliptic is the Sun’s apparent path through the celestial sphere.
The Celestial SphereNorth celestial pole is directly above Earth’s North Pole.
South celestial pole is directly above Earth’s South Pole.
Celestial equator is a projection of Earth’s equator onto sky.
The Milky WayA band of light making a circle around the celestial sphere.
What is it?Our view into the plane of our galaxy.
The Milky Way
The Local SkyAn object’s altitude (above horizon) and direction (along horizon) specify its location in your local sky.
The Local Sky
Zenith: the point directly overhead
Horizon: all points 90° away from zenith
Meridian: line passing through zenith and connecting N and S points on horizon
We measure the sky using angles.
Angular Measurements• Full circle = 360º• 1º = 60 (arcminutes) • 1 = 60 (arcseconds)
Thought Question
The angular size of your finger at arm’s length is about 1°. How many
arcseconds is this?
A. 60 arcsecondsB. 600 arcsecondsC. 60 60 = 3600 arcseconds
A. 60 arcsecondsB. 600 arcsecondsC. 60 60 = 3600 arcseconds
Thought Question
The angular size of your finger at arm’s length is about 1°. How many
arcseconds is this?
Angular Size360 degrees
angular size = physical size 2 distance
An object’s angular size appears smaller if it is farther away.
Why do stars rise and set?
Earth rotates from west to east, so stars appear to circle from east to west.
Our view from Earth:• Stars near the north celestial pole are
circumpolar and never set.• We cannot see stars near the south celestial
pole.• All other stars (and Sun, Moon, planets) rise in
east and set in west.
Thought Question What is the arrow pointing to in the photo below?A. the zenithB. the north celestial poleC. the celestial equator
Thought Question What is the arrow pointing to in the photo below?A. the zenithB. the north celestial poleC. the celestial equator
Why do the constellations we see depend on latitude and time of
year?
• They depend on latitude because your position on Earth determines which constellations remain below the horizon.
• They depend on time of year because Earth’s orbit changes the apparent location of the Sun among the stars.
Coordinates on the Earth Latitude: position north or south of equator Longitude: position east or west of prime
meridian (runs through Greenwich, England)
The sky varies with latitude but not with longitude.
Altitude of the celestial pole = your latitude
Thought Question The North Star (Polaris) is 50° above
your horizon, due north. Where are you?
A. You are on the equator.B. You are at the North Pole.C. You are at latitude 50°N.D. You are at longitude 50°E.E. You are at latitude 50°N and longitude
50°E.
Thought Question The North Star (Polaris) is 50° above
your horizon, due north. Where are you?
A. You are on the equator.B. You are at the North Pole.C. You are at latitude 50°N.D. You are at longitude 50°E.E. You are at latitude 50°N and
longitude 50°E.
The sky varies as Earth orbits the Sun As the Earth orbits the Sun, the Sun appears to
move eastward along the ecliptic. At midnight, the stars on our meridian are opposite
the Sun in the sky.
What have we learned? What does the universe look like
from Earth? We can see over 2000 stars and the Milky
Way with our naked eyes, and each position on the sky belongs to one of 88 constellations.
We can specify the position of an object in the local sky by its altitude above the horizon and its direction along the horizon.
Why do stars rise and set? Because of Earth’s rotation.
What have we learned? Why do the constellations we see
depend on latitude and time of year? Your location determines which
constellations are hidden by Earth. The time of year determines the
location of the Sun on the celestial sphere.