New User Special Price Expires in

Let's log you in.

Sign in with Facebook


Don't have a StudySoup account? Create one here!


Create a StudySoup account

Be part of our community, it's free to join!

Sign up with Facebook


Create your account
By creating an account you agree to StudySoup's terms and conditions and privacy policy

Already have a StudySoup account? Login here

Astronomy Unit 3A

by: Emily Mason

Astronomy Unit 3A Astronomy 1020

Emily Mason

Preview These Notes for FREE

Get a free preview of these Notes, just enter your email below.

Unlock Preview
Unlock Preview

Preview these materials now for free

Why put in your email? Get access to more of this material and other relevant free materials for your school

View Preview

About this Document

This study guides cover all of the Learning Objectives as seen on Blackboard.
Stellar Astronomy
Dr. Flower
Study Guide
50 ?




Popular in Stellar Astronomy

Popular in Department

This 5 page Study Guide was uploaded by Emily Mason on Tuesday March 1, 2016. The Study Guide belongs to Astronomy 1020 at Clemson University taught by Dr. Flower in Winter 2016. Since its upload, it has received 106 views.

Similar to Astronomy 1020 at Clemson


Reviews for Astronomy Unit 3A


Report this Material


What is Karma?


Karma is the currency of StudySoup.

You can buy or earn more Karma at anytime and redeem it for class notes, study guides, flashcards, and more!

Date Created: 03/01/16
Astronomy Unit 3A Learning Objectives—Interstellar Medium  Interstellar Medium- what lies between stars o Includes gas, dust, Electromagnetic radiation between stars, magnetic fields and cosmic rays o The density of the interstellar medium is very low o Much of the interstellar medium’s mass is concentrated in diffuse clouds (made up of atoms and molecules) and molecular clouds (denser than diffuse clouds and made up of mainly molecules) o Intercloud medium- a hot gas between the diffuse atomic and dense molecular cloud 1. Explain why it is difficult for astronomers to piece together the lives of the stars.  With the unaided eye, stars look more or less the same except for brightness and subtle color variations.  Careful observations then reveal many differences between the stars, such as those embodied in the spectral and luminosity class  More detailed observations reveal signs of extreme youth and evidence of old age 2. Describe how interstellar dust contributes to extinction and reddening  Extinction- Immense clouds of dust and gas completely block out the light from stars behind them. This can cause distant stars to appear much fainter than they really are  Reddening- interstellar dust grains are the right size to scatter blue light more than red light. So, more red light than blue light passes through a cloud of dust, causing reddening of starlight and changing a star’s color index.  ***Dust does not affect the observed spectral type of a star because the pattern of spectral lines does not change*** 3. Name the different components of the interstellar medium  Diffuse clouds (see above description)  Molecular clouds (See above description)  Intercloud Medium (See above description)  H II Regions/emission nebulae- the largest visible structures in the interstellar medium which are the bubbles supernovae create. oThey are cavities of ionized hydrogen gas. o When a hydrogen ion recaptures and electron, the electron is “kicked” from the third to second orbital, emitting a red photon. Because of this, H II regions glow from the red light of photons.  Reflection Nebulae- Nebulae that reflect starlight from nearby hot stars off dust particles oSince spectrum of a reflection nebula is the same as that of the stars generating the light, and these stare are hot, main sequence stars (therefore emitting intensely in the blue part of the spectrum), reflection nebulae are blue as well.  Dark nebulae- huge, dark, opaque, dense clouds of dust oExist within the gaseous component of the interstellar medium 4. List the visible features of the interstellar medium (Largest to smallest)  H II Regions (huge bubbles and supernova remnants- x rays and extremely hot gas)  Reflection nebulae / emission nebulae  Dark nebulae 5. List the largest structures of the interstellar medium  H II Regions Learning Objectives—Star formation  Protostar- collapsing condensations in a molecular cloud that are not yet capable of generating nuclear energy but are on their way to doing so. 1. State the physical property of stars that determines how long the different phases of stellar evolution last  Mass determines how long different phases of stellar evolution last. Larger stars go through longer evolutions. 2. The phases that occur during the formation of a star from beginning to end: Dynamic collapse, slow contraction, bipolar molecular outflows, T Tauri phase, Main sequence  Self Gravity- the tendency for atoms, molecules, and dust particles in a molecular cloud or a dense core to feel an attractive gravitational force between each other binding them together. 3. What forces are balanced in a cloud of dust and gas?  A balance between gravity and gas pressure 4. How does mass and temperature control these forces seen above?  Greater massed stars require more pressure to obtain hydrostatic equilibrium (definition below), and to get more pressure they must be hotter. These hot temperatures produce more nuclear reactions/energy, therefore making these stars brighter. 5. Describe the two different triggers of star formation occurring in and near molecular clouds  The supernovae- a gigantic stellar explosion in which most of the mass of a massive star is blasted to space oThe ejected material becomes an expanding shell that compresses gas and dust as it moves through the interstellar medium and can encounter molecular clouds oWhen the shell intercepts a molecular cloud, it can cause the edge of the cloud to implode and initiate star formation.  Galactic Scope o Spiral arms are sites of star formation o Astronomers interpret these arms as being a density wave o When a density wave crosses a molecular cloud, it compresses it and reduces its mass, leading to star formation. 6. Describe how astronomers detect the existence of recently formed protostars  They initially become visible indirectly as embedded infrared sources of radiation within molecular clouds 7. Describe how astronomers detect the thin disks surrounding T Tauri stars  The infrared excess of T Tauri stars is much less than that of embedded protostars, and indicates the existence of only a thin disk.  The disk is what remains after nearly all the dust and gas have fallen onto the protostar or have been blown away  Stellar Birthline- connects the birthpoints for stars of different masses/ the time when the protostar becomes visible. o Most T Tauri stars fall on or below the predicted stellar birthline  HR Diagram Luminosity o ***Higher masses collapse faster!! (10000 to 100000 years)****** o Massive stars, brighter, and hotter stars are located in the top left o T Tauri stars are plotted above the main sequence 8. Describe what stops a protostar from contracting  The protostar reaches hydrostatic equilibrium, in which nuclear reactions at the center provide the energy for its support and supply all the energy that it radiates away, making it a main-sequence star. 9. Describe how astronomers explain the trend in mass and luminosity of the observed mass-luminosity relationship.  Mass-Luminosity relationship- high-mass main sequence stars are more luminous than low-mass stars oAstronomers observed that that the mass-luminosity relationship is dependent on the central temperature of mass oGreater massed stars require more pressure to obtain hydrostatic equilibrium, and to get more pressure they must be hotter. These hot temperatures produce more nuclear reactions/energy, therefore making these stars brighter. Learning Objectives—Stellar Evolution  Main Sequence Stars- any star that is fusing hydrogen in its core and has a stable balance of outward pressure from core nuclear fusion and gravitational forces pushing inward. 1. How do Astronomers determine the age of star clusters? o Star clusters are the result of the collapse of a large segment of a molecular cloud that fragments into hundreds to millions of protostars o We can infer the relative ages of star clusters by the location of the brightest main-sequence stars. Must compare the brightest main sequence stars in each cluster: Whichever one is brightest is younger o We determine the absolute age of star clusters by determining the luminosities and masses of the brightest main sequence stars, then using the lifetime-equation to estimate the cluster’s age. 2. Describe the main sequence turn off of a star cluster o Main sequence turn off- where the brightest stars have already shifted away from their original main sequence positions. o The upper part of the main sequence decreases in luminosity as the stars in the cluster age (this is when they turn off) 3. Order the sequence of events for a star as it becomes a red giant Core hydrogen exhaustion, ignition of nuclear shell source, atmosphere and envelope expand, contraction of the core 4. List the main composition of the cores of: o The main sequence:  Nuclear reactions occur, and the core is made of hydrogen.  The amount of hydrogen is decreasing because the proton-proton chain is gradually converting it to helium.  When the hydrogen is eventually exhausted, the core is completely helium and contractions of the star heat it until nuclear burning occurs. o Stars right after hydrogen exhaustion:  The core contracts until it is heated to 100 million K (making it a red giant) and how has a helium core which undergoes helium burning ( now the core is made of helium) o Stars right after helium exhaustion:  Burn carbon, but this is only if their masses were big enough to keep contractions going  Helium flash- when temperature reach hundreds of millions of K, and the amount of energy generated in the core reaches a hundred time the luminosity of an entire galaxy, creating an enormous outburst of nuclear energy. o After this happens, helium burning is able to occur.  “D” represents the main sequence.  Line “7-8-9” represents the least massive protostar  Line “1-2-3” represents the most massive protostar  “B” represents the birthline  Lines points 4 and 6 represent helium burning, with 4 being the helium flash  Point 2 represents hydrogen core exhaustion


Buy Material

Are you sure you want to buy this material for

50 Karma

Buy Material

BOOM! Enjoy Your Free Notes!

We've added these Notes to your profile, click here to view them now.


You're already Subscribed!

Looks like you've already subscribed to StudySoup, you won't need to purchase another subscription to get this material. To access this material simply click 'View Full Document'

Why people love StudySoup

Steve Martinelli UC Los Angeles

"There's no way I would have passed my Organic Chemistry class this semester without the notes and study guides I got from StudySoup."

Anthony Lee UC Santa Barbara

"I bought an awesome study guide, which helped me get an A in my Math 34B class this quarter!"

Jim McGreen Ohio University

"Knowing I can count on the Elite Notetaker in my class allows me to focus on what the professor is saying instead of just scribbling notes the whole time and falling behind."

Parker Thompson 500 Startups

"It's a great way for students to improve their educational experience and it seemed like a product that everybody wants, so all the people participating are winning."

Become an Elite Notetaker and start selling your notes online!

Refund Policy


All subscriptions to StudySoup are paid in full at the time of subscribing. To change your credit card information or to cancel your subscription, go to "Edit Settings". All credit card information will be available there. If you should decide to cancel your subscription, it will continue to be valid until the next payment period, as all payments for the current period were made in advance. For special circumstances, please email


StudySoup has more than 1 million course-specific study resources to help students study smarter. If you’re having trouble finding what you’re looking for, our customer support team can help you find what you need! Feel free to contact them here:

Recurring Subscriptions: If you have canceled your recurring subscription on the day of renewal and have not downloaded any documents, you may request a refund by submitting an email to

Satisfaction Guarantee: If you’re not satisfied with your subscription, you can contact us for further help. Contact must be made within 3 business days of your subscription purchase and your refund request will be subject for review.

Please Note: Refunds can never be provided more than 30 days after the initial purchase date regardless of your activity on the site.