Questions and Answers
Match the following distinguishing characteristics with the appropriate galaxy type:
Spiral galaxies = Have significant, ongoing star formation Elliptical galaxies = Are more reddish in color
The globular cluster M13 belongs to the ______ component of the Milky Way Galaxy.
halo
A(n) ______ galaxy contains hot, ionized gas but very little cool gas or dust.
elliptical
The type of galaxy known as a(n) ______ galaxy was more common in the universe 10 billion years ago.
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Why is the Hyades Cluster important for building up a catalog of the true luminosities of main-sequence stars?
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What kind of object is the best standard candle for measuring distances to extremely distant galaxies?
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What does Hubble's law tell us?
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According to Hubble's law, if the spectral lines from Galaxy B are redshifted from their rest wavelengths twice as much as the spectral lines from Galaxy A, what can you say about their approximate relative distances?
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Why do virtually all the galaxies in the universe appear to be moving away from our own?
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Estimate the total number of galaxies in the observable universe.
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How was Edwin Hubble able to use his discovery of a Cepheid in Andromeda to prove that the 'spiral nebulae' were actually entire galaxies?
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Which of the following sequences lists the methods for determining distance in the correct order from nearest to farthest?
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Based on current estimates of the value of Hubble's constant, how old is the universe?
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Study Notes
Characteristics of Galaxies
- Spiral galaxies feature a flattened disk of stars and ongoing star formation.
- They contain abundant clouds of cool gas and dust, hosting many bright, hot stars.
- Elliptical galaxies primarily consist of old, low-mass stars and are typically more reddish.
Galaxy Types and Their Properties
- The Milky Way is classified as a spiral galaxy.
- Irregular galaxies were more common approximately 10 billion years ago.
- Elliptical galaxies have hot, ionized gas with minimal cool gas and dust.
Importance of Hyades Cluster
- Closeness allows for stellar parallax measurements, vital for cataloging main-sequence star luminosities.
Cepheid Variables
- Cepheid stars are pulsating variables, with their pulsation periods linked to true luminosities, making them essential as standard candles for distance measurement.
Supernova Brightness and Distances
- If Supernova A is a quarter as bright as Supernova B, it indicates Supernova A is positioned twice as far away.
Measuring Distances to Galaxies
- White dwarf supernovae serve as the best standard candles for gauging distances to extremely distant galaxies.
Hubble's Law
- Indicates that greater distance correlates with higher velocity of galaxies moving away from Earth.
Redshift and Distance Relationships
- Spectral lines from Galaxy B being redshifted more than those from Galaxy A implies Galaxy B is approximately twice as far away as Galaxy A.
Universe Expansion Observations
- All galaxies appear to be receding due to the expansion of the universe, leading to a common observational phenomenon.
Ranking Galaxy Distances and Speeds
- Distance correlates with speed due to universe expansion: galaxies farthest away move fastest.
Total Galaxies in the Observable Universe
- Estimated to be around 100 billion based on galaxy counts in patches of the sky.
Hubble's Discovery
- Hubble utilized the period-luminosity relation of a Cepheid in Andromeda to demonstrate that spiral nebulae were separate galaxies, not part of the Milky Way.
Methods for Distance Measurement
- Accurate distance determination varies by method: starting with parallax for the nearest and progressing to Hubble's law for the farthest.
Age of the Universe
- Current estimates of Hubble's constant suggest the universe is between 12 and 16 billion years old.
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Description
Explore the fascinating characteristics of various types of galaxies, including spiral, elliptical, and irregular formations. This quiz delves into important concepts such as stellar parallax, Cepheid variables, and the implications of supernova brightness on distance measurement.
