Chapter 6: Telescopes

exam 2 flashcards

What controls how much light enters the eye?

The pupil (opens in low light, constricts in bright light)

What is refraction?

A phenomenon that when light hits glass at an angle, it bends.

What is the focus/focal point?

When the light rays hit a lens, causing them to intercept each other at a certain point.

What happens if there is a longer exposure time of an image in cameras?

More light reaches the detector (which is, in a way similar to the retina plane), allowing the camera to capture more details)

What is a pixel?

A picture element

How do pixels work?

When a photon hits a pixel, there is a slight electric charge, and that happens with every pixel, and then the computer measures how many photons/charge there is per pixel, allowing it to conjure a photo.

What are the two most important properties of a telescope?

The light-collecting area and angular resolution.

What does the light-collecting area tell us?

How much light could be collected at one time (usually, with telescopes, we measure size by the lens diameter.

How do you find the difference between two light collecting areas?

Find the ratio between the two (ex: a 10-meter telescope has 5 times the diameter of a 2-meter telescope), and then square that number (so 5² = 25, meaning that the light collecting area is 25 times as great for the 10 meter telescope compared to the 2-meter telescope).

What is angular resolution?

The smallest angle over which we can tell that two dots (or two stars) are distinct. For telescopes, it is the minimum angular separation that the telescope can distinguish.

What is the angular resolution of the human eye?

Around 1 arcminute, meaning about 1/60 degrees.

How do you find the light collecting area?

You can use the diameter to help find it by plugging it into the following equation.

What is the diameter of the largest optical telescope?

10 meters

Where does the limit to resolution come from?

Interference of light waves within a telescope.

Why are larger telescopes capable of greater resolution?

Because there is less interference.

What is the limit on angular resolution called?

the diffraction limit

What are the two basic designs of telescopes?

refracting and reflecting telescopes

What does a refracting telescope do?

it focuses light with lenses

what does a reflecting telescope do?

it focuses light with mirrors.

What type of telescope are most modern ones?

Reflecting ones, due to them being able to have greater diameters.

How are refracting telescopes built?

Very long with large, heavy lenses.

What are some uses of telescopes?

Imaging (pictures of the sky), spectroscopy (breaking light into spectra), and time monitoring (measuring how light output varies with time.

What use can color have in terms of looking farther away using telescopes?

Color can represent different energies of non-visible light.

What does a spectrograph do?

It separates the different wavelengths of light before they hit the detector.

What are some of the best ground-based sites for astronomical observing?

calm and not too windy, high up so there’s less atmosphere to see through, dark and away from lights, and dry so there’s few cloudy nights.

What can be used to help with atmospheric blurring?

Adaptive optics, which rapidly change the shape of a telescope’s mirror to compensate for turbulance.

Which lights pass through earth’s atmospheres?

radio and visible

Which telescopes need to be above the atmosphere to work?

infrared, UV, x-ray, and gamma ray

What are some examples of infrared and UV telescopes?

SOFIA, James Webb, and Spitzer

What are some examples of x-ray telescopes?

Chandra X-ray observatory

What are some examples of gamma-ray telescopes?

Fermi Observatory

What are some other examples of different telescopes?

Neutrinos, cosmic rays, and gravitational waves (example is LIGO).

What is interferometery?

A technique used to link two or more telescopes so they have the angular resolution of a single large one.

Which kind of telescopes is inferometery easiest to do?

radio, but also infrared and visible light.

What are the differences between dwarf planets and regular planets?

They are smaller and may have very elliptical orbits.

How much of the solar system’s mass is attributed to the sun?

Around 99.9% of it.

What is the sun made up of?

Mainly hydrogen and helium (plasma).

How much mass does the sun convert into energy every second?

4 million tons of mass.

Which planet has an extremely large iron core?

Mercury

What is Mercury’s surface and atmosphere like?

Desolate, cratered with long, tall, and steep cliffs, without any atmosphere

What are the conditions like on Venus?

Surface is hidden by sulfuric clouds (which make the planet very bright), and the conditions are very bad bc of the extreme greenhouse effect.

What are the conditions on Mars like?

Giant volcanoes, a huge canyon, polar caps, etc.. Signs of water, meaning potential past life.

What are the four Galleon moons of Jupiter?

Io, Calisto, Ganymede, and Europa.

What is Jupiter composed of?

Mostly H/He

How much larger is Jupiter compared to Earth?

Around 300 times.

How many moons of Jupiter are there?

67 (but now reported to be 95)

What is a defining feature of Io?

there are active volcanoes all over

What is a defining feature of Europa?

A possible subsurface ocean

What is a defining feature of Ganymede?

The largest moon in the solar system (Zeus’s Favorite)

What is a defining feature of Calisto?

It is a large, cratered “ice ball”

What is one of Saturn’s defining features?

It’s spectacular rings, which are not solid, and are really ice and dust and rock orbiting Saturn.

What is Uranus composed of?

H/He gas alongside hydrogen compounds (H20, NH3, CH4)

Which planet has an extreme axis tilt?

Uranus

What is a defining feature of Uranus?

It has 27 moons and rings.

How many moons does Neptune have?

14 moons, including Triton (his son!!)

What are some of the dwarf planets?

Pluto, Eris, and others.

What is Pluto’s main moon, and what is a defining feature?

Charon (charon works with Hades hehe), and it is nearly the same size

What are some key features of terrestrial planets?

Smaller size/mass, higher average density, made mostly of rocks and metals, solid surface, few if any moons and no rings, usually closer to the sun and together, equaling warmer surfaces.

What are some key features of jovian planets?

Larger size/mass, lower average density, made mainly of H, He, and H compounds, no solid surface, rings and many moons, farther from the sun and each other = cooler temps at cloud tops.

Which process created the elements from which the terrestrial planets were made?

Nuclear fusion in the stars

Which planet has an odd rotation?

Venus: it spins clockwise (technically, also Uranus bc it spins on its side)

What is one similarity between all the planets in the solar system?

All the larger bodies orbit in the same direction and almost in the same plane

How do we learn the scale of the solar system?

Using two points on earth and observations during the transit (when Venus was in front of the sun), we were able to measure the parallax angle, meaning that we could calculate the distance to Venus. Essentially, we used Kepler’s third law.

What is a flyby?

A flyby mission flies by a planet only once. (cheapest, but we don’t get that much information from it

What is an orbiter?

A spacecraft that goes into orbit around another world, and can gather more data than a flyby, but not very detailed info.

What is a probe or lander?

They land on the surface of another world and explore the surface in detail.

What is a sample return mission?

A spacecraft that is designed to land on another world, gather samples, and return to earth.

What are some examples of sample return mission spacecrafts?

Apollo to the moon, and Hayabusa to an asteroid.

What properties of the solar system must a theory be able to explain?

1. Patterns of motion of the large bodies (orbit and plane)

2. existence of two types of planets

3. existence of smaller bodies (asteroids and comets)

4. notable exceptions to usual patterns (size of earths moon, rotation of Uranus and Venus, etc.)

What does the nebular theory state?

That our solar system formed from the gravitational collapse of a giant interstellar gas cloud, also known as the solar nebula.

Which theory is widely accepted?

The nebular theory

What is the close encounters hypothesis?

A idea that proposed that the planets were formed from debris torn off the sun by a close enounter with another star.

Why is the close encounters theory not very probable?

Because it can’t explain observed motions and the types of planets.

What is one point of support for the nebular theory?

We can see stars forming in other interstellar gas clouds, alongside with seeing disks around other stars..

Which conservation law supports the nebular theory?

The conservation of Angular momentum, stating that the rotation speed of the cloud must have increased when the cloud contracted.

What were some consequences of there being collisions between particles in the cloud?

the cloud flattened into a disk while shrinking, there were less random motions (especially up and down ones).

What is the frost line?

The point where inside it, it is too hot for hydrogen compounds to form ice, while outside it is cold enough for ices to form.

How did the terrestrial planets form?

Small particles of rock and metal were present inside the frost line, and due to the process of accretion, these planetesimals became planets.

What is accretion?

When gravity assembles planetesimals into terrestrial planets.

Where did comets and asteroids come from?

they were leftovers from the accretion process. asteroids = inside frost line, comets = outside frost line

Where did water on earth come from?

A bombardment of icy planetesimals

What may be the origin of unusual moons, and what are some examples?

They may be captured planetesimals, and some examples would be phobos and deimos

What is one possible explanation for our moon?

a planetesimal hit earth, shatterin eath and the planetesimal, and then the planet was completely molten, and the debris splashing out and the shattered planetesimal formed the moon in the process of accretion.

What is a possible explanation for odd rotation?

Giant impacts, usually done by planetesimals.

How would the solar system be different if the solar nebula had cooled, with a temperature half its actual value?

Jovian planets would have formed closer to Sun.

What caused the orderly patterns of motion in our solar system?

Solar nebula spun faster as it contracted because of conservation of angular momentum. Collisions between gas particles then caused the nebula to flatten into a disk.

Why are there two major types of planets?

Only rock and metals condensed inside the frost line. Rock, metals, and ices condensed outside the frost line. Larger planetesimals outside the frost line drew in H and He gas.

Where did asteroids and comets come from?

They are leftover planetesimals, according to the nebular theory

How do we explain "exceptions to the rules"?

Bombardment of newly formed planets by planetesimals may explain the exceptions.

How do we know the age of the solar system?

Through radiometric dating (which tells us that the oldest moon rocks are 4.4 billion years old), and the oldest meteorites are 4.55 billion years old.

Who misinterpreted the surface features of Mars and believed it to be canals?

Percival Lowell

What happened to the early craters on Mars?

They have been erased

What is the geology of Mars like?

There are many shield volcanoes, what looks like dry riverbeds, the erosion of craters, and signs of water.

What is the largest volcano in the solar system, and where is it?

Olympus Mons on Mars

How did the system of valleys known as the “Valles Marineras” originate? Where is it?

from plate tectonics, on mars.

What are martian rocks?

Rocks that appear to have formed in water, or rounded pebbles that are commonly found in streams.

Which solid planet has the least impact craters?

Venus

What kind of volcanoes does Venus have?

shield and stratovolcanoes

How do we know that there was most likely tectonics on venus?

Due to the fractured and contorted surface.

Are there still tectonics on Venus? Why?

No, unknown but theories state because of weaker convection, or a more rigid lithosphere. Now, there is a lack of plate tectonics.