1. Devil physics The baddest class on campus IB Physics

2. Astrophysics Tsokos Option E-1 Introduction to the universe

3. IB Assessment Statements
Option E-1, Introduction to the Universe: E.1.1. Outline the general structure of the solar system. E.1.2. Distinguish between a stellar cluster and a constellation. E.1.3. Define the light year.

4. IB Assessment Statements
Option E-1, Introduction to the Universe:
E.1.4. Compare the relative distances between stars within a galaxy and between galaxies, in terms of order of magnitude.
E.1.5. Describe the apparent motion of the stars/constellations over a period of a night and over a period of a year, and explain these observations in terms of the rotation and revolution of the Earth

5. Objectives Describe the main features of the solar system.
Name the main objects making up the universe.
Give the definition of a light year.

6. Objectives
State the average distances between stars and between galaxies.
Outline the main facts about the motion of stars as they appear to an observer on earth.

7. Order of Magnitude
Scales of the Universe

8. The Solar System
OBJECTIVE: Describe the main features of our solar system
Called a solar system because it is a system of planets and moons that rotate around a star, specifically the sun

9. The Solar System
The sun has a mass of 1.99x1030 kg and a radius of 6.96 x 108 m
The Sun is a main sequence G2 star that contains 99.86% of the system's known mass.
Its two largest orbiting bodies, Jupiter and Saturn, account for 91% of the remainder.
Consists of 8 major planets in elliptical orbits around the sun
Pluto now considered a “dwarf planet”
The sun constitutes one of the two foci of the elliptical orbits
The earth’s orbit is nearly circular
The orbit of Mercury is the most elliptically shaped

10. The Solar System
Consists of 8 major planets in elliptical orbits around the sun
Pluto now considered a “dwarf planet”

11. Relative Orbit Radii This is the inner solar system
The sun constitutes one of the two foci of the elliptical orbits
The earth’s orbit is nearly circular
The orbit of Mercury is the most elliptically shaped

12. Relative Orbit Radii
This is the outer solar system

13. Relative Orbits
The planes of the orbits of the planets differ only slightly from the plane of the earth’s orbit
The exception to that is Mercury which has a 7-degree inclination
All the planets and most of the comets orbit the earth in the same direction
The most famous exception to this is Halley’s comet

14. Laws of Gravitation and Planetary Motion

15. Kepler’s Laws
The motion of an object that is attracted and bound to a heavier mass is, according to the law of gravitation, an ellipse or circle.
Planets sweep out equal areas in equal times.
The period of a planet around the sun is proportional to the 3/2 power of the orbit radius.
Motion of the planets and comets about the sun is dictated by Kepler’s Laws
The moons that orbit the planets also follow Kepler’s laws

16. Moons
All the planets except Mercury and Venus have moons that orbit around them
The earth’s moon has a period of 27.3 days
Jupiter has 16 moons, 4 of which are as big as our moon

17. Moons
Saturn has 17 moons

18. Saturn
Because of it’s size, Saturn attracts a large amount of objects (in the millions) that orbit the planet in a coplanar circular ring

19. Pluto Pluto was thought to have only one moon, Charon
Since Charon is nearly as large as Pluto, the two may be thought of as a binary system where they rotate about their center of mass

20. Asteroid Belt
In the region between the orbits of Mars and Jupiter is an asteroid belt
Consists of thousands of small objects, really small planets, in orbit around the sun
The largest of these is Ceres which has a diameter of 770 km

21. Characteristics of Planets
Relative sizes of the planets
Listed in order of their distance from the sun
Mass is proportional to radius
Period is proportional to radius IAW Kepler
Note that Neptune has a period of just under 164 years

22. Characteristics of Planets
List of the planets by size from smallest to largest

23. Characteristics of Planets
Size and acceleration due to gravity relative to the earth
In other words, if the earth’s radius is 1, Jupiter’s radius is 11.2 times the earth’s radius, it has 318 times the mass of the earth and the gravity on the surface is 2.6 times that of earth.

24. Objective
Name the main objects making up the universe

25. Beyond the Solar System
Here is a half of the list of terms which you will become acquainted with by the end of this unit
The list is on page 490 of the book
You should read through it now so that the terms are familiar when they come up

26. Beyond the Solar System
Here is the other half of the list

27. Objective
Give the definition of a light year

28. Light Year
The distance light will travel in one year

29. Objective
State the average distances between stars and between galaxies

30. Parsec (pc) Represents the average distance between stars in a galaxy
Parsec is a useful number to have
The average distance between stars is 1pc
The distance to the nearest star, Proxima Centauri, is about 1.3pc from earth which is 4.3ly and 4x1016 m away
The distance between galaxies in the same cluster is about 100pc, and a few Mpc between galaxies of different clusters

31. Objective
Outline the main facts about the motion of stars as they appear to an observer on earth

32. Motion of the Stars
Observing the movement of the stars is complicated by the fact that the earth is also moving
You may notice that stars seem to move from east to west, but their relative position remains the same
Early notion of a celestial sphere rotating about the earth
Polaris, the north star, doesn’t appear to move because it is aligned with the North Pole of the earth’s axis of rotation

33. Motion of the Stars
The earth’s axis precesses in a circle that traces out a cone
The period of the precession is about 26,000 years
In AD 14,000, the earth’s axis will point to the start Vega

34. Motion of the Stars
Using a long exposure, this is the pattern stars will trace in a given night.

35. Motion of the Stars
As the earth rotates about the sun in the course of the year, different portions of the night sky appear visible
The position of the stars change by about 1-degree per day
This is where the astrological charts come from
The different months correspond to the different constellations that are visible

36. Objectives Describe the main features of the solar system.
Name the main objects making up the universe.
Give the definition of a light year.

37. Objectives
State the average distances between stars and between galaxies.
Outline the main facts about the motion of stars as they appear to an observer on earth.

38. IB Assessment Statements
Option E-1, Introduction to the Universe: E.1.1. Outline the general structure of the solar system. E.1.2. Distinguish between a stellar cluster and a constellation. E.1.3. Define the light year.

39. IB Assessment Statements
Option E-1, Introduction to the Universe:
E.1.4. Compare the relative distances between stars within a galaxy and between galaxies, in terms of order of magnitude.
E.1.5. Describe the apparent motion of the stars/constellations over a period of a night and over a period of a year, and explain these observations in terms of the rotation and revolution of the Earth

40. questions?

41. Homework
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