Chapter 10

Chapter 10What we know about the universe has taken us thousand of years1Celestial BodiesCelestial Body: a natural object out in space such as a planet, a moon, an asteroid, a comet, or a star

Star: like our sun, give off heat and light and are thousands of years away

Planets: a celestial body that orbits one or more stars, is large enough that its own gravity holds it in a spherical shape, and is the only body occupying the orbital path.

2Constellations

ConstellationsConstellations: a distinctive pattern in the night sky formed by a group of stars. It often looks like a familiar object like an animal.Examples: Ursa Major or the great bear, Ursa Minor or the little bear, Orion the hunter,

Asterisms: smaller groups of stars forming patterns within the constellations. Example: the big dipper (found in Ursa Major)4Ursa Major

5Orion

Orion is one of the brightest constellations and is a mythological characterAccording to Greek myths, Orion was a hunter who used to brag all the time. This bother the gods.When the gods were tired of him, the sent a scorpion to bite and kill him.The gods felt bad for doing having Orion killed, they placed him in the skyUrsa Minor

Motion of Cellestial bodiesSun follows the same path through the sky everyday and the path is called ecliptic.

Ecliptic: the path followed by the Sun through the sky, as seen from Earth.

8Apparent path of the Sun as seen from Earth

9Motion of planetsThey follow an ecliptic path called orbits around the Sun,which are long, slightly flattened circles.These orbits result from gravitational forces As the Earth revolves around the Sun, it appears that the Sun is moving against the background of stars As the planets revolve around the Sun, they move at different rates along an ecliptic path depending on their distance from the sun

10Planet motion

11Motion of PlanetsThose inside Earths orbit (Mercury and Venus) appear to race through the sky and appear to be close to the SunThose beyond Earths orbit are slower (Mars) and appear far from the Sun in the sky. Seem to move against the background of stars in the sky

12Motion of Asteroids and Comets Both Orbit around the sunAsteroids: one of many small rocky bodies in our solar system, most of which orbit the Sun between Mars and Jupiter.

13Comet orbitThe orbits of comets can be above or below the orbit of Earth, for this reason we do not always see the comet on the eclipticThey can orbit in different planes (unlike all other planets)

Visit to explore the orbits of comets and asteroids www.spaceplace.nasa.gov/en/educators/comet_orbits_cnsr.pdf14Comets Orbit the Sun

15Motion of the MoonThe moon orbits around Earth once every 28 days.

16Other motion..Planets, suns (stars) and moons spin on a central axis. Earth spins on its axis, which is an imaginary line from the North Pole to the South PoleRemember:celestial bodies move in cyclic paths called orbits and that these orbits result from gravitational forces.Example: the Earth spins on its axis towards the east. Stars, including the Sun, all generally move from east to west.

17Early Models and Evidence Gathered about the UniverseAristotle: saw the universe as geocentric the Earth at the center and the sun, moon, planets and stars revolving around it.

Patterns of stars does not change so he thought the Earth was in a fixed place

During a lunar eclipse, the shadow cast on the moon had curved edges so Earth must be a sphere.

18Aristotles Evidence that Earth is Sphere

1920Early models

Ptolemy: He noticed that the motion of Mars in the sky over several weeks creates a loop in the sky. This change in direction is called retrograde motion.21Early modelsTo explain this motion, Ptolemy proposed that each planet revolved around a point on its orbit, called an epicycle, to explain its motion through the heavens

22Early modelsCopernicus: he thought the earlier observations could be explained in a simpler way by a model in which Earth rotated on its axis once daily and revolved around the Sun once a year. (Heliocentric model)

The Earths motion around the Sun is relatively recent (1543)

23Galileo: First person to turn a small telescope towards the sky and publicly report what he saw.Observed craters on the moon, spots on the sun, and four stars orbiting Jupiter.

Galileo also observed that Venus had phases like our moon does and this could only happen if Venus orbited the Sun

25Johannes Kepler: with the help of Tycho Brahe, made observations of Mars orbit and found that it modeled an ellipse (oval shape)Kepler developed three laws of planetary motion

26Sir Isaac NewtonHe was the first to show mathematically that the force of gravity reaches far beyond the surface of Earth and affects all celestial bodiesThis force causes the bodies to remain in orbit around larger bodiesInvented the reflecting telescope which allowed more precise observations.27Early Technologies for observations Stone Circles: possibly used to make simple astronomical observations. For example, Stonehenge. On midsummers day the Sun rises directly over a particular stone in Stonehenge. Marking the longest day of the year.

Sun rising over a stone 28Early TechnologiesAstrolabe: around the time of Ptolemy, they were used to help locate and predict the positions of the Sun, Moon and starsUsing a compass and an astrolabe, they were able to describe the position of any celestial body in relation to the direction North as well as in relation to the horizon.

ASTROLAB ACTIVITY: http://cse.ssl.berkeley.edu/AtHomeAstronomy/activity_07.html

29TechnologiesTelescope: Refracting telescope (uses lenses to gather and focus light) was used by Galileo to make his observations (Sun centered universe)

Reflecting Telescope: (uses mirrors to gather and focus light) was developed by Newton to make even more precise observations and this design is used today, called the Newtonian design30Core LabStrolling Through the Solar System31