An Introduction to Astronomy Cairo University Faculty of Physical Therapy General Education Program By Dr. Zainab Mohamed Awad Astronomy, Space Science, & Meteorology Department Faculty of Science - Cairo University 2014 Lec. 10
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An Introduction to Astronomy
Cairo UniversityFaculty of Physical TherapyGeneral Education Program
By
Dr. Zainab Mohamed AwadAstronomy, Space Science, & Meteorology Department
Faculty of Science - Cairo University
2014 Lec. 10
2
In Lecture 9
Stellar Distribution (H-R diagram)
Binary systems
The formation and evolution of stars
The ISM Life Cycle
Stars – P2
General Education Program An Introduction to Astronomy
3
In Lecture 10
Galactic Morphology
Our Galaxy: the Milky Way
The Local group of Galaxies
Large scale structures (P1)
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Galactic Morphology
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What is a galaxy?- A galaxy is a collection of stars, gas and dust bound
together by their common gravitational pull.
Size range:
104 - 2x105 Ly
Brightness:
109 - 1014 Lsun
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The Triangulum Galaxy (M33) @ 2.9 million Ly awayimage from NASA's Spitzer Space Telescope
Structure & TypesCommon features of galaxies
1- gravity holds the stars together
2- the densest region is in the center (core or bulge)
3- all galaxies have a faint outer region or envelope and
a mysterious dark matter halo
4- some galaxies have spiral arms
General Education Program An Introduction to Astronomy 6HST ultra deep field galaxies
Main components of a galaxy
- Nucleus (core/bulge) - The halo (envelope)
- The dark halo (invisible)
- The disc (with arms – exists ONLY in disc type galaxy)
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General Structure
Structure & Types
Galaxy Colours:
The galaxy different components have various types of
stars.
Young stars (hot stars) in discs give them their blue
colour, while older stars (cool stars) in the bulge/halo let
them appear red.
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Structure & Types
Morphological Types- According to their shapes, galaxies can
be divided into 3 main categories
1- elliptical galaxies
2- disc galaxies
3- irregular galaxies
- These classes are known as
morphological types
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- There are other morphological types of
galaxies such as mergers, but these other
types are not in the scope of this course.
Morphological Types
1- Elliptical 2- Disc Irregular
2.1- Normal spiral
2.2- Barred spiral
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Morphological Types
1- Elliptical 2- Disc Irregular
2.1- Normal spiral
2.2- Barred spiral
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Other Morphological Types
1- Merging galaxies 2- Interacting galaxies
Hubble image of two merging spiral galaxies
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Types & PropertiesHubble Sequence
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Types & PropertiesHubble Sequence
Our Galaxy: the Milky Way
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The Milky Way Galaxy
Our galaxy “the MilkyWay” is an example of adisc galaxy of the barredspiral subclass
The solar system is located in the galactic disc @ 28000 Ly from the galactic centre on the local arm “Orion”.
Barred spiral
Edge-on diagram of the M.W
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The Milky Way Galaxy
In the late 18th Century, long before distances to starswere known, William Herschel tried to estimate thesize and shape of our Galaxy
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The Structure of our GalaxyGeneralStructure
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The Structure of our GalaxyGeneral Structure
General Properties
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General Properties
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General Properties
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Motion
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General properties of the MW regions
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General properties of the MW regions
The arms are:
- Cygnus
- Carina-Sagittarius
- Norma
- Crux-Scutum
- Perseus
Perseus
Orion local Cygnus
Carina-Sagittarius Crux-Scutum
Sun
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The Structure of our Galaxy
The Milky Way GalaxyA simulation of the Galaxy structure
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Measuring the MW
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Measuring the MW
William Herschel tried to estimate the size and shape ofour Galaxy by counting the stars but he did notrecognize that the “voids” are actually dusty regions.
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Measuring the MW
Variable stars within the galaxy gives a good estimationabout the distance within the galaxy up to 25 Mpc.
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Formation of the MW & Spiral Arms
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Formation of the MW
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Theories of formation of spiral arms
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Density wave theory
Density waves move through galaxy compressing
matter as it passes and setting off star formation
like traffic jam formation on highway
Theories of formation of spiral arms
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Density wave theory
Density waves move through galaxy compressing
matter as it passes and setting off star formation
like traffic jam formation on highway
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self-propagating star formation (or Supernovae
chain reaction)
Supernovae send out waves which creates new
stars and subsequent supernovae.
So stars are formed in specific regions that appear
as arms and over time the regions fade as stars
burn out, or drift away
Theories of formation of spiral arms
The Local group of Galaxies
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The Local Group of Galaxies
rich clusters:
containing thousands of galaxies, D ~ 3 Mpc
poor clusters:
hundreds or less galaxies, D ~ 1 Mpc
The local group is classified as “poor cluster” with about 30 galaxy.
A galaxy cluster is a group of many galaxies.
HST; Abell Cluster of Galaxies
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The Local Group of Galaxies
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The Local Group of Galaxies
The Local Group of Galaxies
Local group most famous members:
MW,
Leo I, Leo II,
Sextant dwarf,
Umi dwarf,
Draco dwarf,
LMC, SMC,
Andromeda (M31)
Pinwheel (M33)
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