Download Chapter 18 - Department Of Computer Science

Phys141 Principles of Physical Science
Chapter 18
The Universe
Instructor: Li Ma
Office: NBC 126
Phone: (713) 313-7028
Email: [email protected]
Webpage: http://itscience.tsu.edu/ma
Department of Computer Science & Physics
Texas Southern University, Houston
Nov. 24, 2004
Topics To Be Discussed

The Sun
 The Life Cycle of Stars
 Galaxies
 Skip
– §18.2 The Celestial Sphere
– §18.3 Classifying Stars
– §18.6 Cosmology
The Universe

The totality of all matter, energy, and space
 In this chapter, stars, galaxies, and the
celestial sphere will be discussed
 Milky Way Galaxy is only a tiny part of our
universe
 Our solar system only occupies a very small
volume of Milky Way Galaxy
The Sun
The Sun is a star – a self-luminous sphere of
hot gas
 The hot gas is held together by gravity and
energized by nuclear reactions in its core
 The diameter of the Sun is almost four times
the distance between the Earth and the Moon

The Sun (cont)

Table 18.1 on page 460
– diameter, mass, density, distance from the Earth,
and so on

Figure 18.1 on page 460
– A cross-sectional view of the Sun

The bright, visible “surface” of the Sun is
called photosphere
– The distinct feature of the Sun’s surface is the
periodic occurrence of sunspots
The Sun (cont)

Sunspots are huge patches of cooler material
on the surface of the Sun
– Figure 18.2 & 18.3 on page 461

The number of sunspots appearing on the
Sun varies over an 11-year sunspot cycle
The Life Cycle of Stars
In general, a star’s life cycle is: be born,
radiate energy, expand, possibly explode, and
then die
 The exact details depend on a star’s mass
and its composition
 The greater the mass of a star, the faster it
moves through its life cycle

The Life Cycle of Stars (cont)

The life cycle of low-mass stars is:
protostar, main-sequence star, red giant,
planetary nebula, and finally white dwarf
 Stars may increase in brightness by a factor
of 100 to millions in hours
 A star undergoing such a drastic increase in
brightness is called a nova, or “new” star
The Life Cycle of Stars (cont)

A nova is the result of a nuclear explosion on
the surface of a white dwarf
 Supernova is a gigantic explosion of stars
 A Type II supernova results from the
collapse of the iron core of a massive red
supergiant, leaving behind either a neutron
star or a black hole
The Life Cycle of Stars (cont)

Evolution of a high-mass star is: when they
leave the main sequence, they become
supergiants and eventually explode as Type II
supernova, scattering much of their material
into space and leaving behind a neutron star,
or in the case of most massive star, a black
hole
– Figure 18.23 on page 477
Galaxies

A galaxy is an extremely large collection of
stars bound together by mutual gravitational
attraction
 Galaxies are the fundamental components of
the structure of the universe
 Our solar system occupies a relatively small
volume of space in very large system about
100 to 200 billion stars known as Milky Way
Galaxy
Galaxies (cont)

Galaxies have been classified into 4 types
based on how they look in photographs:
–
–
–
–

Elliptical galaxy
Normal spiral galaxy
Barred spiral galaxy
Irregular galaxy
Milky Way Galaxy is a normal spiral galaxy
Assignment

Homework Assignment
– Review Questions (page 488 – 489):

3,4,32,40,44,49,50
– Exercises (page 490):

3 (steps of calculation are required since answer is
already given in the book)
– It’s due Monday, 12/6/04