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

Week 4 Notes

by: Emily Notetaker

Week 4 Notes ASTR 1504 - 300

Emily Notetaker
GPA 3.9

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

These notes cover material from this week's lectures and chapters 4 and 5 from the book.
Astronomy: Exploring the Universe
Xinyu, Dai
Class Notes
25 ?




Popular in Astronomy: Exploring the Universe

Popular in Astronomy

This 10 page Class Notes was uploaded by Emily Notetaker on Friday February 12, 2016. The Class Notes belongs to ASTR 1504 - 300 at University of Oklahoma taught by Xinyu, Dai in Spring 2016. Since its upload, it has received 17 views. For similar materials see Astronomy: Exploring the Universe in Astronomy at University of Oklahoma.


Reviews for Week 4 Notes


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: 02/12/16
Astronomy Week 4 Chapter 4 Spectrographs/spectrometers- tools that take the spectrum of an object, split the light by wavelength, then record it. Atoms and molecules add light to particular wavelengths, causing emission lines, and take light away from other wavelengths, causing absorption lines. As a result, each type of atom or molecule has a unique set of lines, like a fingerprint. Astronomers can look at the light from a distant object through a spectrograph and use the emission and absorption lines to determine what the object is made of. This process is called Spectroscopy. Resolution- the smallest details that can be separated and observed Diffraction- the distortion that occurs as light passes the edge of an opaque object Diffraction limit- the best resolution that a given telescope can achieve. Angular Resolution- how small of an angle two object can be separated by and still be distinguished by the telescope. αmin=1.22xλ/D αmin- angular resolution 1.22- constant λ- wavelength D- aperture Angular Resolution is measured in arcseconds 1 degree=60 arcminutes 1 arcminute=60 arcseconds 1 degree=3600 arcseconds Astronomical Seeing- limitation of angular resolution caused by the atmospheric distortions. Pockets of air at different temperatures and pressures diffract light unevenly and distort images collected by telescopes. There are two solutions Space based telescopes- By launching a telescope into orbit; scientist can observe light without atmospheric distortions because it is being collected outside of the atmosphere Adaptive optics- Telescopes with adaptive optics measure the wave crests as light enters the telescope, then calculate the distortion and, using a mirror with a flexible surface, compensate for the distortion. Adaptive optics can allow Earth-based telescopes to achieve image quality that rivals that of the Hubble Space Telescope. Not all of the electromagnetic spectrum can penetrate Earth’s atmosphere. Gamma- rays, X-rays, and most of the infrared region are absorbed by the atmosphere before reaching Earth, so to study them astronomers must use either airborne observatories in high flying planes or space telescopes. Radio Telescopes- Radio waves are able to make it through the atmosphere fairly easily, so radio telescopes work well on the ground. Because radio waves have the longest wavelengths, radio telescopes need to have a very wide diameter, and still have relatively poor resolution. Interferometric Arrays-Several telescopes that combine data. By combining the data from multiple radio telescopes, astronomers can increase the diameter and achieve better angular resolution. Chapter 5 Molecular Clouds- dense cool clouds of dust and gas in the space between stars, primarily composed of hydrogen molecules Self-gravity- gravitational attraction among all parts of the same object. Can be balanced by gas pressure in a molecular cloud. Hydrostatic Equilibrium- state of balanced forces within a molecular cloud In some molecular clouds the internal gas pressure will be low enough that the cloud will begin to collapse under its own self-gravity Areas of the molecular cloud that are denser collapse more quickly, so the cloud fragments into multiple Molecular-cloud Cores instead of a single object. As the cores collapse into themselves, the molecules within them become closer together, so the force of gravity on them increases, causing the collapse to speed up. The collapse of central layers of the molecular cloud near the cores leave the outer layers without support to counter the force of gravity, so they begin to fall inwards. Protostar- innermost part of a collapsing molecular cloud Gravitational energy is converted to thermal energy as the cloud collapses, causing the surface of the protostar to glow. As the protostar becomes denser, particles within it begin colliding with one another, increasing the thermal energy. This thermal energy produces infrared light. The protostar maintains constant balance between the force of hot gas pushing outwards and the force of gravity pushing inwards, even as both of these forces constantly increase. A protostar becomes a star when its center becomes hot enough to begin converting hydrogen into helium. This process is called nuclear fusion, and the new star draws energy from this rather than gravitational energy in order to produce light and radiation. In order to begin converting hydrogen to helium and become a star, a protostar much reach a temperature of 10 million K. To reach this temperature, a protostar must be at least 0.08 times as massive as the Sum (0.08 M ) A protostar that is too small to reach 10 million K is known as a brown dwarf. At the same time as the star is forming, the gas and dust not pulled in the protostar forms a flattened rotating disk known as and accretion disk. Angular Momentum- a conserved quantity of a revolving or rotating system with a value that depends on both the velocity and distribution of the mass. If the diameter of the object rotating decreases, the speed of rotation increases, and vice versa. Conservation of Angular Momentum- the angular momentum must remain the same in the absence of an external force Particles collapsing from above and bellow the protostar have no effect on the angular momentum. Most of them land within the accretion disk, where they all rotate in the same direction around the protostar. The diameter of the accretion disk keeps the velocity of rotation relatively slow, which allows the protostar to grow without moving so fast that it pulls itself apart. Once the protostar becomes a star, the accretion is called the protoplanetary disk. All objects in the solar system are formed from the disk. Small particles collide and stick together, or are blown into larger particles by gas motion. Larger groups of particles sweep up smaller objects in their path. Planetesimal- an object within the protoplanetary disk that is about 1 km across. Large enough to begin pulling smaller nearby objects into it with its gravity. As the planetesimal pulls in all other objects near its orbit, its growth rate increases until it eventually becomes a planet. Large planets may form their own accretion disks, which form moons. Dwarf planets, comets, and asteroids are planetesimals left over from this process. Because of the heat of the protostar, different material will settle at different points in the accretion disk. Refractory materials such as metal and rock, which can reach very high temperatures without melting or evaporating, are found close to the center of the disk. Volatile materials such as water ice ammonia and methane, which melt and evaporate at moderate temperatures, are found farther from the protostar where the temperature is low enough for them to maintain a solid form. Primary Atmosphere- gas captured from the disk by the planet’s gravity during its formation. Mostly hydrogen and helium. Large planets such as Jupiter keep the primary atmosphere while smaller planets don’t have enough gravity to do so. Secondary Atmosphere- gas released from a planet’s interior due to volcanoes Planet- round body orbiting a star that has cleared other objects from its orbit and is smaller than 13 Jupiters Terrestrial Planets- planets formed near the center of the accretion disk from refractory materials Giant Planets- planets formed near the edge of the accretion disk from volatile materials. Most of their mass is made of gas Dwarf Planets- orbit a star but have not cleared other bodies from their orbit Exosolar Planet- a planet orbiting a star other than our sum. The first exosolar planet was discovered in 1992. There are 5 methods used to locate exosolar planets. 1. Radial Velocity Method- a planet’s gravity causes the star it orbits to move slightly. Observing this movement allows astronomers to calculate the planet’s mass and distance from the star. The Doppler Effect is used to detect movement from the star.  The Doppler Effect causes a shift in the light an object produces when the object is in motion. The waves in front of the object will be closer together causing the light to appear more blue, so the light is blueshifted when the object is moving towards you. The waves behind the object will be further apart causing the light to appear more red, or redshifted, when the object is moving away. 2. The Transit Method- when a planet passes in front of the star it orbits, the star’s light will diminish slightly. By continuously measuring the brightness of a star astronomers can detect this slight change of brightness 3. Gravitational Lensing- the gravitational field of a planet acts as a lens, so if the planet passes in front of a background star, the star’s brightness will slightly increase. The effect of this is so small that it is typically called microlensing. 4. Astrometry- precisely measuring the location of a star in the sky. A planet’s gravity will cause the star to move in a mini orbit, which can be detected using astrometry if the system is viewed from above. This movement is very tiny and difficult to measure, but does not require the system being observed to be on the same plane as Earth, unlike the previous methods. 5. Direct Imaging- directly taking a picture of the planet. This is difficult because the bright light from the star makes it nearly impossible to see dim planets nearby. Even when an object is observed, continued observation is needed to ensure that it is orbiting the star and not simply a background object, and to confirm that it’s a planet and not a brown dwarf. Hot Jupiters- planets similar to Jupiter that orbit their stars more closely than Mercury orbits the Sun. Most likely formed near the edge of the stars accretion belt then migrated inwards. Many of the early exoplanets discovered were hot Jupiters, because their large masses and close proximity to their stars cause the stars to move a lot and be easily detected by the radial velocity method. They are also more likely to pass in front of their stars and be detected by the transit method. Habitable Zone- area within a star system where liquid water can exist


Buy Material

Are you sure you want to buy this material for

25 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."

Kyle Maynard Purdue

"When you're taking detailed notes and trying to help everyone else out in the class, it really helps you learn and understand the I made $280 on my first study guide!"

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."

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.