Universe Chapter 1- Part 1

Question 1

What is the Universe (Cosmos)?

Answer 1

the Universe is what contains everything around us

such as: Galaxies, stars, planets, nebulae, supernovas, pulsars, blackholes, quasars, interstellar dust…

Question 2

What represents all visible matter?

Answer 2

The stars represent all visible matter

Question 3

What is the Universe composed of?

Answer 3

4% visible matter
23% dark matter
73% dark energy
0.005% electromagnetic radiation

Question 4

What is the unit used in Astronomy?

Answer 4

Astronomical Unit (AU)
it's used to measure distance in our solar system

Question 5

What is the value of the AU in Earth-Sun distance?

Answer 5

1UA= 150x10^6 km

Question 6

What is a light-year?

Answer 6

Light year is the distance traveled by light in vacuum during ONE year

Question 7

How is a light year calculated?

Answer 7

D= V x t
(Note that t= 1 year= 31557600sec)
D= 300000 x 31557600= 9.47 x 10^12 km

Question 8

What is 1LY equal to?

Answer 8

1LY= approximately 10^13

Question 9

What made up the Universe? Universe Expansion?

Answer 9

The Galaxies, grow apart from each other so that the Universe as a whole expands. Big Bang event

Question 10

When did the expansion begin?

Answer 10

13.7 BILLION years ago

Question 11

Big Bang event occurred..

Answer 11

Space and Time, matter and energy were created

Question 12

How was the BIG BANG formed?

Answer 12

• Very hot mixture (matter + energy)
• quarks and leptons appear
• formation of neutral universe ( neutrons, protons, electrons)
• Formation of light elements nuclei ( ratio H:He was 3:1)
• Universe Cold (electrons + nuclei combine into atoms)
• Formation of stars and galaxies from dust and gas clouds

Question 13

What are galaxies?

Answer 13

Galaxies are building blocks of the universe

Galaxies are grouped into small groups -> galactic clusters

Question 14

What is the large part galaxies composed of ?

Answer 14

It’s invisible (dark matter)

Question 15

What are the regions of Galaxies:

Answer 15

Celestial Bodies (planets, asteroids, comets)
Gases
Interstellar dust
Stars ….

Question 16

What are the THREE classes of Galaxies?

Answer 16

1) Elliptical Galaxies (2/3)
2) Spiral Galaxies (1/4)
3) Irregular Galaxies ( <1/10)

Question 17

What does Elliptical Galaxies contain?

Answer 17

• few young stars
• little gas & dust
• many old red stars

Question 18

What does Spiral Galaxies contain?

Answer 18

• alot bright young stars
• rich in gas and interstellar dust
• few old red stars

Question 19

What does Irregular Galaxies contain?

Answer 19

change their appearance due disturbance from large galaxies near by

Question 20

The Milky Way (our Galaxy)

Answer 20

• diameter=130,000 LY & thickness=10,000 LY
• large galaxy with 200 B stars
• has a black hole in it’s center

Question 21

What are stars?

Answer 21

Stars are giant balls of gas that represent building blocks of galaxies

Question 22

What are Stars responsible for?

Answer 22

Production and distribution of elements ( Carbon, Nitrogen, oxygen…)

Question 23

What are the CHARACTERISTICS (stellar properties) of Stars?

Answer 23

. Surface Temperature: determined by finding the part of its spectrum having MOST intense radiation
are in between: 3000 to 12000 k (up to 400000 k)
- Hottest: BLUE-WHITE
- Intermediate: YELLOW ORANGE
- Coldest: RED
. Distance: LUMINIOSITY expresses the total amount of energy radiated in space per unit time (power)
Absolute magnitude shows how bright a star appears at specific distance 32.6 LY from earth (True brightness)
* Apparent Magnitude* shows brightness of star as we see from Earth
. Diameter (size): is determined from surface temperature and luminosity
temperature: indicates how much radiation is emitted
luminosity: measures TOTAL radiation of entire surface of star

Question 24

How is the relationship (temperature- absolute magnitude) shown?

Answer 24

shown by H-R DIAGRAM Hertzsprung-Russell

Question 25

How is the position of the star determined on the H-R diagram?

Answer 25

it's related to its physical properties

Question 26

HR diagram (stars on it) :

Answer 26

- Upper end: large hot bodies - lower: small, dense, reddish, and colder - middle: medium like our SUN, has moderate temperatures, densities, masses and average diameters * STARS are STABLE on the main sequence (HS)

Question 27

What are some of the WHITE dwarfs properties?

Answer 27

has warm surface, low radiation, small stars, very dense.

Question 28

What are the properties of Giants?

Answer 28

Low density, high volume, high absolute magnitude, low surface T

Question 29

Into how many categories are stars classified into?

Answer 29

2 Categories: Population 1: located in central disk of galaxy, many young stars, rich in heavy elements Population 2: located in halo of central zone of galaxy, old stars, poor in heavy elements

Question 30

What is the Cause of the death of stars?

Answer 30

Hydrogen reserves depleted --- gravitational pressure >> nuclear pressure --- contraction --- rise in temperature --- fusion of helium (further rxns with heavier nuclei only for massive stars occurs)

Question 31

How are stars born?

Answer 31

Stars are born in clouds, composed of Hydrogen & Helium with small amount of nebulae (heavier atoms: C, N, O). These clouds have low density, in rotation. Some regions of nebulae contract under effect of gravity. Speed of rotation increases >> collapse >> central nucleus formed & a PROTOSTAR few million years later temperature rise and H & HE fuse forming a STAR

Question 32

From where does the star get its energy?

Answer 32

From Hydrogen Fusion rxns into Helium, this energy maintain a sufficient pressure to allow resist the collapse under gravitational pressure of upper layer's weight

Question 33

When star is in hydrostatic equilibrium:

Answer 33

its size remains stable, reaches a phase called MAIN SEQUENCE

Question 34

Main Sequence is divided into TWO phases:

Answer 34

- can be very short, hundreds of thousands of years if the star is massive - can be longer, several billion years if the star's mass similar to SUN's

Question 35

Death of STARS will undergo different fates which are ?

Answer 35

. Sun-like Star: passing through red giant phase, star shrinks to white dwarf state. Shell of gas from star comes out into space to form planetary nebula. Shines for billion years then will stop shining and come back to be a black dwarf. . Massive Star: passing through supergiant phase, undergoes violent explosion in Supernova causing formation of heavy elements sending these elements into space. IN THE END, a neutron star is formed, if it's more massive it'll remain as a black hole.