Module 7 Flashcards
Why are most astronomical observatories located on Earth’s surface?
Ground-based telescopes are much less expensive to build, operate, and maintain than telescopes in space.
What are the primary problems that Earth’s atmosphere poses for astronomical observations?
The primary problems are:
* Daylight and weather
* Scattering of human-made light (light pollution)
* Blurring of images by atmospheric motion
* Most forms of light cannot reach the ground
What is light pollution?
Light pollution is the scattering of bright lights from cities at night, which hinders astronomical observations.
How does atmospheric blurring affect ground-based telescopes?
Atmospheric turbulence bends light, causing images to jiggle, limiting the angular resolution to about 0.5 arcsecond.
What technology is used to reduce atmospheric blurring in telescopes?
Adaptive optics.
How does adaptive optics work?
Adaptive optics adjusts the shape of telescope mirrors to counteract atmospheric distortions.
What criteria do astronomers consider when locating ground-based observatories?
Astronomers consider:
* Dark sites (limiting light pollution)
* Dry sites (limiting rain and clouds)
* Calm sites (limiting turbulence)
* High altitude (above part of the atmosphere)
Name three important locations for ground-based astronomical observatories.
- Mauna Kea, Hawaii
- La Palma, Canary Islands
- Paranal Observatory, Chile
What is the main advantage of putting telescopes into space?
Space telescopes are unaffected by Earth’s atmosphere.
What types of light can the Hubble Space Telescope observe?
Hubble can observe infrared, ultraviolet, and visible light.
True or False: Space telescopes are closer to the stars than ground-based telescopes.
False.
What is the significance of observing light across the electromagnetic spectrum?
Different astronomical objects emit light over a broad range of wavelengths, which is crucial for understanding the universe.
List the types of light that can be observed from the ground.
- Radio waves
- Visible light
- Very long wavelengths of ultraviolet light
- Small parts of the infrared spectrum
What are the three key factors to consider when choosing a personal telescope?
- Light-collecting area (aperture)
- Optical quality
- Portability
What is the James Webb Space Telescope designed for?
It is optimized for infrared observations to study distant galaxies.
What is the primary function of radio telescopes?
They collect radio waves from cosmic sources.
Fill in the blank: The most common type of telescope in the world is the _______.
satellite dish
What are the differences between satellite dishes and astronomical radio telescopes?
Satellite dishes are designed for communication satellites and are stationary, while astronomical radio telescopes point toward cosmic radio sources that rise and set with Earth’s rotation.
What is essentially a small radio telescope?
A satellite dish
Satellite dishes and astronomical radio telescopes differ in size and purpose.
How do communication satellites orbit Earth?
In geostationary orbits
They orbit above Earth’s equator in sync with Earth’s rotation.
What is the primary purpose of astronomical radio telescopes?
To point toward cosmic radio sources
Unlike satellite dishes, which do not make images.
Why are astronomical radio telescopes larger than satellite dishes?
They need a large light-collecting area and decent angular resolution
This is necessary for detecting faint radio waves.
What is angular resolution?
The ability to distinguish between two closely spaced objects
It is crucial for making images with telescopes.
What is the world’s largest single radio telescope?
China’s Five-hundred-meter Aperture Spherical Telescope (FAST)
FAST was completed in 2016.
What is the angular resolution of FAST compared to the Hubble Space Telescope?
About 1000 times worse
FAST has an angular resolution of approximately 1 arcminute.
What technique allows radio telescopes to achieve better angular resolution?
Interferometry
This technique links multiple telescopes for enhanced resolution.
What is the main challenge for radio astronomy?
Radio-wave pollution
This pollution from human activity can drown out cosmic signals.
What is SOFIA?
NASA’s airborne observatory carrying a 2.5-meter infrared telescope
It observes infrared light from high altitudes.
What interferes with observations from infrared telescopes?
Infrared thermal radiation from Earth and the telescope itself
This heat can obscure the cosmic infrared signals.
What is the only major space observatory capable of ultraviolet observations?
The Hubble Space Telescope
No major new ultraviolet observatories are currently near completion.
Why must x-ray telescopes be placed in space?
No cosmic x-rays reach the ground
Earth’s atmosphere absorbs x-rays.
What are grazing incidence mirrors used for?
To deflect x-rays in x-ray telescopes
They allow x-rays to be focused without penetrating the mirrors.
What is the purpose of gamma-ray observatories?
To capture gamma rays using massive detectors
They cannot focus gamma rays in the traditional sense.
What are the three types of cosmic messengers mentioned?
Neutrinos, cosmic rays, gravitational waves
These are different from light and provide additional information about the universe.
What is interferometry?
A technique that links multiple telescopes to improve angular resolution
It relies on the wavelike properties of light.
What is the Karl G. Jansky Very Large Array (JVLA)?
A radio telescope array consisting of 27 individual dishes
It can achieve high angular resolution through interferometry.
What is the significance of the Event Horizon Telescope project?
It captured the first image of a black hole
The image shows the shadow of a black hole in galaxy M87.
What is the main goal of the chapter on the Sun?
To study the Sun’s structure and energy generation
The Sun serves as an introduction to the study of stars.
What ancient ideas existed about the Sun’s energy source?
Worship as a god and mythological explanations
Ancient peoples recognized the Sun’s importance but did not understand its energy source.
Why is the Sun’s energy vital to human existence?
The Sun’s energy is essential for life on Earth and has been worshipped and mythologized by ancient peoples.
What was the ancient belief about the Sun’s source of energy?
Ancient thinkers imagined the Sun to be some type of fire, like burning coal or wood.
What significant discoveries were made in the mid-19th century regarding the Sun?
The Sun’s distance and size were measured, allowing scientists to calculate its true energy output.
What is gravitational contraction?
Gravitational contraction is the process where a shrinking gas cloud heats up as gravitational potential energy is converted into thermal energy.
How long could gravitational contraction theoretically keep the Sun shining?
Gravitational contraction could keep the Sun shining for up to about 25 million years.
What breakthrough did Einstein’s theory of relativity provide concerning the Sun’s energy?
Einstein’s theory showed that mass contains enormous potential energy, leading to the understanding that the Sun generates energy through nuclear fusion.
What conditions are necessary for nuclear fusion to occur in the Sun?
Nuclear fusion requires extremely high temperatures and densities found deep in the Sun’s core.
What is gravitational equilibrium?
Gravitational equilibrium is the balance between the outward push of internal gas pressure and the inward pull of gravity.
What is energy balance in the context of the Sun?
Energy balance is the rate at which fusion releases energy in the Sun’s core matching the rate at which the Sun radiates energy into space.
How long will the Sun continue to shine steadily?
The Sun was born with enough nuclear fuel to last about 10 billion years and is currently about halfway through this lifetime.
What is the Sun primarily composed of?
The Sun is made almost entirely of hydrogen and helium.
What is the radius of the Sun?
The radius of the Sun is just under 700,000 kilometers.
How massive is the Sun compared to Earth?
The Sun’s mass is about 300,000 times the mass of Earth.
What is the Sun’s total power output, or luminosity?
The Sun’s luminosity is about 3.8 x 10^26 watts.
What is the corona?
The corona is the outermost layer of the Sun’s atmosphere, extending several million kilometers above the visible surface.
What temperature does the corona reach?
The temperature of the corona is about 1 million K.
What is the chromosphere?
The chromosphere is the middle layer of the solar atmosphere, radiating most of the Sun’s ultraviolet light.
What is the photosphere?
The photosphere is the visible surface of the Sun, with an average temperature just under 6000 K.
What is the convection zone in the Sun?
The convection zone is where energy generated in the solar core travels upward through rising hot gas and falling cool gas.
What happens in the radiation zone of the Sun?
In the radiation zone, energy moves outward primarily in the form of photons of light.
What is the temperature at the Sun’s core?
The temperature at the Sun’s core is about 15 million K.
What is nuclear fusion?
Nuclear fusion is the process of combining two or more small nuclei into a larger nucleus, generating energy.
Fill in the blank: The Sun generates energy through the process of _______.
nuclear fusion
True or False: The Sun’s energy generation is similar to that of nuclear reactors on Earth.
False
What process do nuclear power plants use to generate energy?
Nuclear fission
Fission involves splitting large atomic nuclei, such as those of uranium or plutonium.
What is the process called when the Sun generates energy by combining small nuclei?
Nuclear fusion
Fusion combines two or more small nuclei into a larger nucleus.
What is the temperature of the plasma in the solar core?
15 million K
This extreme temperature is essential for nuclear fusion to occur.
What force is responsible for allowing positively charged nuclei to fuse?
The strong force
It binds protons and neutrons together in atomic nuclei and can overcome electromagnetic repulsion.
What is the role of high temperatures in nuclear fusion?
They increase the energy of collisions between nuclei
Higher temperatures make fusion reactions more likely.
What is the proton-proton chain?
A sequence of steps in the Sun’s fusion process
It begins with collisions between individual protons.
What is produced when two protons fuse in the first step of the proton-proton chain?
Deuterium
Deuterium is an isotope of hydrogen consisting of one proton and one neutron.
What happens in the second step of the proton-proton chain?
A deuterium nucleus fuses with a proton to form helium-3
Helium-3 is a rare form of helium with two protons and one neutron.
What is the final product of the proton-proton chain?
Helium-4 nucleus
This occurs after the third step, which involves the fusion of helium-3 nuclei.
How much hydrogen does the Sun fuse into helium each second?
600 million tons
This process converts about 4 million tons of matter into energy each second.
What is the percentage of energy released in fusion that emerges as kinetic energy of helium nuclei and gamma rays?
About 98%
The remaining 2% is carried off by neutrinos.
What does the solar thermostat regulate?
The Sun’s core temperature and fusion rate
It ensures that the energy produced equals the energy radiated.
What happens if the Sun’s core temperature rises slightly?
The fusion rate increases, causing the core to expand and cool
This restores the original temperature and energy balance.
What is radiative diffusion?
The slow outward migration of photons through the Sun’s interior
Photons bounce randomly among electrons before escaping to space.
What is the average temperature of the gas in the Sun’s photosphere?
About 5800 K
The photosphere is where photons can escape to space.
What are the three ways we learn about the Sun’s interior?
Mathematical models, solar vibrations, solar neutrinos
Each method provides insights into the Sun’s internal conditions.
What is the main purpose of mathematical models of the Sun?
To predict internal conditions using the laws of physics
These models help estimate temperature, pressure, and density at various depths.
What does a model of the Sun’s interior predict?
Radius, surface temperature, luminosity, age, and other observable properties of the Sun.
What method uses vibrations of the Sun’s surface to learn about its interior?
Helioseismology.
What type of waves do vibrations in the Sun’s surface resemble?
Sound waves.
What do Doppler shifts in solar vibrations indicate?
Movement of gas on the Sun’s surface.
What is the solar neutrino problem?
The initial detection of only one-third of the expected solar neutrinos.
What are the three types of neutrinos?
- Electron neutrinos
- Muon neutrinos
- Tau neutrinos
What law describes the pressure in the Sun?
The ideal gas law.
How does the pressure in the Sun’s core compare to Earth’s atmospheric pressure?
About 200 billion times greater.
What causes sunspots to appear dark?
They are cooler than the surrounding photosphere.
What is the temperature of plasma in sunspots?
About 4000 K.
What keeps sunspots cooler than their surroundings?
Strong magnetic fields.
What phenomenon occurs when magnetic fields cause spectral lines to split?
The Zeeman effect.
What are solar prominences?
Giant loops of gas that extend high into the Sun’s corona.
What are solar flares?
Intense storms that emit bursts of ultraviolet light and x-rays.
What happens to magnetic field lines during a solar flare?
They snap and reorganize into a less twisted configuration.
What is the main source of x-rays from the Sun?
The corona.
Fill in the blank: The gas temperature in the Sun’s core is approximately _______ K.
15 million
True or False: Neutrinos interact with matter through the electromagnetic force.
False.
What is the primary method for detecting solar neutrinos?
Using large detectors placed underground or under ice.
What is the role of strong magnetic fields in the chromosphere and corona?
They carry energy upward and contribute to heating.
What is solar activity?
Phenomena such as sunspots and solar flares that affect Earth.
What is the temperature of the Sun’s corona?
Approximately 1 million K.
What happens to the core pressure during the fusion of hydrogen into helium?
It decreases.
Fill in the blank: The Sun’s luminosity gradually _______ with time.
increases
What is the effect of solar storms on Earth?
They can affect day-to-day life.
What is the typical lifespan of an individual sunspot?
Up to a few weeks.
What is the temperature of the plasma in the chromosphere?
Approximately 10,000 K
The chromosphere emits strongly in the ultraviolet.
What is the temperature of the plasma in the corona?
Approximately 1 million K
The corona is the source of virtually all x-rays from the Sun.
What phenomenon allows us to see the chromosphere and corona during a total eclipse?
The bright photosphere is blocked from view
This allows the lower density gases of the chromosphere and corona to be visible.
What are coronal holes?
Regions of the corona that are nearly devoid of hot coronal gas
These areas barely show up in x-ray images.
What is the source of the solar wind?
Particles streaming outward from the corona
These particles escape the Sun through coronal holes.
What are coronal mass ejections (CMEs)?
Large bubbles of highly energetic charged particles ejected from the Sun’s corona
They can create geomagnetic storms when they reach Earth.
What effects can coronal mass ejections have on Earth?
They can create geomagnetic storms that lead to:
* Strong auroras
* Disruption of radio communications
* Damage to electrical power systems
* Damage to spacecraft electronics
How often does the sunspot cycle occur?
Averages 11 years
However, it can vary between 7 to 15 years.
What happens to sunspot locations as the sunspot cycle progresses?
Sunspots form primarily at midlatitudes and then move towards lower latitudes
They appear close to the solar equator as the cycle approaches the next solar minimum.
What unusual behavior occurs to the Sun’s magnetic field at solar maximum?
The Sun’s entire magnetic field flips
This results in a complete magnetic cycle averaging 22 years.
What historical period is known for virtually no sunspots?
The Maunder minimum
This occurred between 1645 and 1715.
What can be used to estimate past solar activity?
The amount of radioactive carbon-14 in tree rings
Carbon-14 production varies with solar activity.
What is the leading model for the cause of the sunspot cycle?
A combination of convection and the Sun’s rotation
Convection amplifies magnetic fields while the Sun’s rotation shapes them.
How does the Sun’s rotation affect magnetic field lines?
The equator rotates faster than the poles, causing magnetic lines to become more twisted
This twisting contributes to the generation of sunspots.
Does the Sun’s total output of energy change significantly during the sunspot cycle?
No, changes are less than 0.1% of the Sun’s average luminosity
However, ultraviolet and x-ray output can vary more significantly.
What is the relationship between solar activity and Earth’s climate?
Some data suggest correlations, but the Sun’s energy output has been steady despite recent global warming
This indicates that human activity is the primary driver of recent climate change.
True or False: The solar wind is composed of particles that are only produced in coronal holes.
False
The solar wind originates from the corona, not exclusively from coronal holes.
Fill in the blank: The sunspot cycle can affect the frequency of _______ and _______ during solar maximum.
prominences, flares
These events are most common at solar maximum.
