Unit 2 - Astronomy New Worlds Celestial Objects and Stars

Earth Science

Solar System

A system of planets, dwarf planets, asteroids, meteors, satellites (i.e. moons), and comets that are “captured” in orbit around a central Star or Stars

• Smaller part of a galaxy

What is the age of our solar system?

~4.568 (4.6) billion years old

Nebular Hypothesis 

• Jeans Instability/Jean’s Mass and length

1. When a nebular cloud contains a certain amount of debris (mass) and has reached a certain size (diameter), the likelihood of cloud contraction is high

• Gravitational collapse of a small part of a giant molecular cloud (sweeping/accretion)

• Theory of how our solar system was formed

Stage 1 - Nebular Hypothesis 

• Nebular Cloud

Stage 2 - Nebular Hypothesis 

• Nebular Disk 

Stage 3 - Nebular Hypothesis

Planetesimals Form

Stage 4 - Nebular Hypothesis

Stable Solar System with Planets 

What is needed to make a planet?

1. Sweeping

2. Accretion 

Sweeping

• Gathering of surrounding debris by rotational forces 

Accretion

• Initially small particles of gas and dust stuck together via their electrostatic attraction

• As they grew larger, their gravity became strong enough to attract particles as well, and their growth accelerated 

• Once large enough gravity pulls the planetesimal into a spherical shape  

Chemical Differentiation

• A process in which heavy elements sink towards the center of an object while the lighter elements remain closer to the surface

• This is the reason that internal structures of planets are dense, rocky, and heavy

• Solar wind blows out the remaining nebular gases which helped form the large gaseous atmospheres of the Jovian planets

Terrestrial Planets

• “Earth Like”

• Inner 4 most planets

• Bodies of mostly rock

• Mercury, Venus, Earth and Mars 

Mercury

• Closest planet to sun

• 2nd hottest planet - - - - ~180 degrees C to 430 degrees C

• No atmosphere/no greenhouse effect

• Smallest

• No satellites (moons)

Venus

• 2nd from sun

• Hottest planet!!!!!

• Thick atmosphere of CO2/Large greenhouse effect

• Temps: ~465 degrees C to -175 degrees C

Earth

• Only known to have life!!!

• Only planet to have Vast amounts of water 

Mars

• Red Planet - Has high amounts of Fe

• Largest Volcano in S.S. Olympus Moons

• Geologically active

• Thin atmosphere of CO2

• Similar temps and seasons to that of Earth

• Frozen Water at its poles 

General Characteristics of All Terrestrial Planets

1. Small radii, low mass, high density

2. None to very thin atmospheres

3. Craters, canyons, and Volcanoes can be present

Asteroid Belt

Separates the Terrestrial planets from the Jovian planets

Jovian Planets

• “Jupiter Like”

• Outer 4 most planets

• Gas Giants

• Jupiter, Saturn, Uranus, Neptune 

Jupiter

• 92% Gas (Hydrogen & Helium)

• Great Red spot (~300yrs) Cyclonic Storm

• Total Mass twice that of all other planets 

Saturn

• Has rings ~150 km thick (Made from Rock and Dirty Ice)

• 930 mi/hr winds

• Less dense than Water (.7)

Uranus

• Mostly Methane Gas gives it a Blue-green color

• Very strange Rotation. It rotates tipped 98 degrees on its side 

Neptune

• Great blue spot

• ~1,100 mi/hr winds (strongest in Solar System) Faster than the speed of sound!

General Characteristics of all Jovian Planets 

1. Large radius, high mass, and very low density

2. Thick Atmosphere Composed of primarily gases. H2, He and some CH4

3. Solid Cores of the planets are believed to exist deep under the gases

4. All have ring systems

Planet Classification

• Planet - is in orbit around the Sun

• Has sufficient for it’s self-gravity to overcome rigid body forces so that it assumes a nearly round shape

• Massive enough to clear the neighborhood around its orbit. Does not share it’s orbit!

Dwarf Planet

• Is in orbit around the Sun

• Has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a nearly round shape

• Has not cleared the neighborhood around its orbit. It shares an orbit

• Is not a satellite of another planet

Smaller Solar System Bodies

This category collectively refers to all other celestial bodies orbiting our Sun, (including asteroids, comets, and satellites)

What 2 regions is the residual debris of our solar system locked in?

Trans neptunian object/orbit

• The Kuiper Belt

• The Oort Cloud

The Kuiper Belt

An area composed largely of frozen volatiles (termed “ices”), such as Methane,ammonia and water bodies beyond the orbit of Neptune.

• 30 to 50 AU from the sun

The Oort Cloud

• A theoretical cloud containing “dirty ice” well beyond the orbit of the Kuiper Belt

• A sphere thought to be between 2,000 and 200,000 A.U. away from the sun

• 80% of all known comets have originated here

Possible Oort Cloud Bodies:

• 2000 CR105

• 2006 SQ372

• 2008KV42

A Star

• A massive, luminous sphere of gas/plamas held together by gravity

• Composed primarily of hydrogen along with helium and trace amounts of heavier elements caused by nucleosynthesis

Solar Structure

• The sun is completely gaseous

• Mainly Hydrogen (74%) and He (24%)

• The Sun is not burning (5,500 degree C - 15,000,000 degrees C)

• Energy comes from Nuclear fusion

• 5 billion years old (lifespan = ~10 Bil.)

• Solar energy is nearly pollution free

Sun’s Rotation

The Sun Rotates every 25.6 to 36 days depending on Solar Latitude and it’s axial tilt on is ~7.25 from the axis of the Earth’s orbit

Why isn’t the sun burning?

• There is nothing to burn because of fusion

• Looks yellow/orange because of wavelength and frequency emitted from Sun

What 2 forces keep the sun in equilibrium?

• Gravity caused by large mass (inward)

• Kinetic Pressure - gasses pressing (outward)

3 features of the sun

• Solar Prominences

• Solar flares

• Sunspots 

Solar Prominences

Arcs of gases can shoot tens of thousands of miles from the Sun’s surface PROMINENCES bounce & walk along the Surface

Solar Flares

Violent eruptions that shoot into space

Sunspots

• Cooler, darker regions on the Sun’s surface

• Cause changes in the Earth’s weather patterns and can interfere with Electrons, devices, solar cycles 

What kind are relationships are sunspots?

Cylic

• (~11 year cycle)

Sunspot - Max

• High Solar Activity

Sunspot - Minimum

• Low Solar Activity

The 6 layers of the Sun

1. Core

2. Radiative Zone

3. Convection Zone

4. Photosphere

5. Chromosphere

6. Corona

Core

Fusion:Creates Energy

Radiative Zone

Transfers Energy out of Core

Convection Zone

Circulation of Energy outward towards the surface due to changing density 

Photosphere

The Sun’s visible Surface and Lower Atmosphere

• Yellow in color

Chromosphere

The Sun’s Middle Atmosphere

• Red in color 

Corona

The Sun’s Outer Atmosphere

• Only visible during Total Solar Eclipse 

• ~ 7 minutes of Totality

Does distance affect brightness?

• Objects that are close appear brighter

• Objects that are farther away appear dimmer 

Stellar Magnitude

Ways to measure a star’s brightness (Emission of light)

Apparent Magnitude (brightness)

A measure of how bright a star Appears in the night sky. Depends on a star’s:

(Distance & Luminosity)

• A bright star has a (negative #)(lower #)

Ex: - 3.2

• A dimmer star has a (positive #)(higher #)

Ex: +2.7

Absolute Magnitude

The apparent magnitude a star would have if it were 32.6 light years from Earth (Depends on Radiant Energy ONLY)

• A bright star has a (neg. #) or (lower #)

Ex:-1.8

• A dim star has a (pos #) or (higher #)

Ex: +2.9

How do Astronomers Classify Stars?

1. Apparent Magnitude

2. Absolute Magnitude

3. Luminosity 

Magnitudes we need to know

Polaris

• Apparent = 2.0

• Absolute = -3.7

Sun

• Apparent = - 26.8

• Absolute = 4.9

Moon

• Apparent = -12.6

• Absolute = N/A

Sirius

• Apparent = -1.5

• Absolute = 1.4

Luminosity

The total output of radiant energy per second.

Depends on: Temperature, mass, & radius

A star with a Luminosity of 100 gives off radiant energy that is 100 times (Greater) than the sun

Luminnosity Scale:

Ranges from (high) 100,000 to .00001 (low)

The sun = 1

The Sun’s Luminosity

The Sun is just an Average Star

Average In:

1. Luminosity

2. Temperature

3. Mass

4. Radius/Diameter

5. Age

2 factors of Luminosity

• Size/radius

• Temperature 

Luminosity - Size

A bigger star is more luminous than a smaller one of the same temperature 

Luminosity - Temperature

A hotter star is more luminous than a cooler one of the same radius

Luminosity Relationships

• As Temperature (of a star) increases

Luminosity? Increases

• As Mass (of a star) decreases

Luminosity? Decreases

• As the radius/diameter

Luminosity? Increases

Temperature’s Effect on a Star’s color

• As temperature (of a star) increases, it’s color will appear white to blue

• As temperature (of a star) decreases, it’s color will appear orange to red

Stellar Evolution

• Stellar evolution refers to the large-scale, systematic changes of the structure and composition of a star over time

• Initial mass of a star is overwhelmingly the property that determines the evolutionary path that the star will follow 

Sequence of Stellar Evolution for Stars Similar in Mass to the Sun

1. Stars as a stellar dust and gas (Nebula)

2. Gravity pulls material together and forms a large mass “Protostar”

3. Gravity continues to collapse the proto star and fusion causes emission of light “Main Sequence Star”

4. As H2 is fused into HE the star will begin to increase in size due to a loss is Mass and a decrease in Gravitational attraction (Red Giant)

5. When all the HE is used up the outer envelope of the star is ejected out (planetary nebulae and the core collapses)(white dwarf). The star then dims until it is no longer giving off light and becomes very small (black dwarf)