Astronomy 100 - Midterm 1

What is the celestial sphere?

A model of a domed surface that all stars sit on surrounding Earth.

What is the ecliptic equator?

The sun's orbit relative to us, does NOT align with the celestial equator

What is a circumpolar zone?

The area surrounding a pole in which the stars circle completely above the horizon?

What prominent constellation is in the circumpolar zone and can be seen at all times from Oberlin?

The Big Dipper

What are constellations?

88 sectors that divide the sky

When is the sun higher in the sky?

Summer

How long does the sun stay in each zodiacal sign?

One month

What model of the solar system is correct?

Heliocentric

What does the geocentric model use to explain retrograde?

Epicycles

What is retrograde?

A planet appears to move backwards because planets closer to the sun move faster than those that are further, overtaking them and producing apparent backward motion.

How did Venus prove that the heliocentric model is correct?

Galileo could see the whole of Venus at some points, rather than just the crescent that would be visible in the geocentric model.

Kepler's 1st law

Objects in our solar system travel in ellipses around the sun.

Kepler's 2nd law

Equal areas take equal time

Is a planet moving faster or slower when it is closer to the sun?

Faster

What is a focus?

One of two points within an eclipse where the sum of their distance to the edge at any point is always equal.

What is eccentricity?

How non-circular and orbit is.

1 AU (Astronomical Unit)

The distance between the Earth and the Sun

What is longitude?

Degrees between your meridian and Prime Meridian

What is latitude?

Degrees from the equator

What is "sky latitude" called?

Declination, measured in degrees

What is "sky longitude" called?

Right Ascension, measured in time (24 hrs)

Where is the "prime meridian" of right ascension?

Vernal equinox

Why is the sun in the sky for more hours during the summer?

It is North of the celestial equator

Why do certain parts of Earth get more sun at specific times, causing seasons?

Earth's 23 degree tilt

What happens during the summer solstice (Jun 21) in the Northern Hemisphere?

Sun is around 23 degrees North of the equator, placing it at the zenith at noon in the Tropic of Cancer. the Arctic Circle is fully illuminated 24 hrs per day.

What happens during the winter solstice (Dec 21) in the Southern Hemisphere?

Sun is around 23 degrees South of the equator, placing it at the zenith at noon in the Tropic of Capricorn. The Antarctic Circle is fully illuminated for 24 hrs per day.

What is it called when the sun crosses the celestial equator?

Equinox (vernal or autumnal)

Why can we see over the horizon?

The atmosphere refracts light.

When does twilight begin and end?

When the sun is 18 degrees below the horizon.

What is at one of the foci of each planet's orbit?

The sun (technically)

How many degrees does the moon move per day?

12

Why are there not eclipses twice a month?

Due to the angle of the moon's orbit, the Earth's shadow rarely blocks it from the sun.

What does it mean for the moon to be "tidally locked"?

Moon rotates with the Earth, so we always see the same side of it.

What distorts the Earth into a slightly oblong shape?

All parts of Earth are not equally distant from the pull of the moon, causing different forces of attraction at different places.

What causes tides on the side of the Earth closest to the moon?

gravitational pull on water

What causes tides on the side of the Earth farthest from the moon?

Inertia: The water on the far side of Earth is not being pulled as much as the "middle", which causes a bulge.

Why can we expect two high tides a day?

Each place on Earth passes through each bulge once a day.

What happens to the tides when the sun and moon are aligned (full or new moon)?

Higher tides/spring tides

What happens when the sun and moon are not aligned (1/4 or 3/4 moon)?

Lower tides/neap tides

Why do the sun and moon look to be the same size in our sky?

The sun is 400 times bigger, but the moon is 400 times further away.

What is an umbra?

A cone that is the darkest part of a shadow caused by a sphere

What is a penumbra?

A region of shadow caused by a sphere that is less dark.

How many times a year do we experience an "ecliptic season"?

2

Why do "total solar eclipses" only happen at certain points on Earth?

The moon's umbra will only hit a certain point on Earth, and all other areas will be in the penumbra and see a partial eclipse.

Why are total lunar eclipses more common?

The Earth's umbra can easily cover the entire moon, making it more likely that a total eclipse will occur.

When will a new moon rise and set?

Rise at 6:00AM, set at 6:00PM

When will a full moon rise and set?

Rise at 6:00PM, set at 6:00AM

Shorter wavelengths produce what color of light?

Blue (hotter, faster moving particles)

Longer wavelengths produce what color of light?

Red (cooler, slower moving particles)

What is the charge of atomic nuclei?

Positive

What is the charge of an electron?

Negative

What causes magnetism?

The electric attraction and repulsion of moving charges within an atom.

What produces an electric field?

Stationary charges

What produces a magnetic field?

Moving charges

What causes radiation waves?

Oscillation between changing magnetic fields that change electric fields, which change magnetic fields, etc.

At what speed to wavelengths travel?

All wave lengths travel at the speed of light.

What is frequency?

The number of wave crests per second. Longer wavelengths = lower frequency, shorter wavelengths = higher frequency.

What is a photon?

Light that behaves like a packet of energy, carrying specific amount of energy proportionate to their frequency if the light was in waves.

Describe gamma rays

Shortest wavelengths, dangerous for humans. Blocked by our atmosphere.

Describe X-rays

Penetrates flesh, but not bone. Too many atoms to penetrate Earth's atmosphere in large amounts.

Describe ultraviolet rays

High energy rays that do not penetrate Earth's atmosphere for the most part. Some reach us, causing cancer.

Describe visible light

A wavelength of light visible to the human eye, we evolved to see it because it penetrates our atmosphere best.

Describe infrared radiation

Heat radiation absorbed by water and Co2 in Earth's lower atmosphere.

Describe microwaves

Small compared to radiowaves, these rays are absorbed by water and good for heating food.

Describe radiowaves

Wide range of wave types from 1 meter to hundreds of meters in length, include radar, AM, FM, TV

What is a blackbody?

An idealized object that does not reflect or scatter radiation, only absorbs it.

What happens when a blackbody absorbs energy?

The speed of the blackbody's molecules will become faster, making the blackbody hotter until absorption and radiation are in balance.

Why does a blackbody emit a spectrum of wavelengths?

Some particles of the blackbody are moving slower than average, and others are moving faster. This produces different wavelengths.

What is reflection?

Light bouncing off a given surface (direction of light beam can be calculated when it reflects off of a smooth, shiny surface)

What is refraction?

Light is bent when it passes from one transparent material to another.

What is dispersion?

Different wavelengths of light are bent by different amounts of refraction.

What is a spectrometer?

An instrument used to disperse wavelengths and form a spectrum.

What is a continuous spectrum?

An array of all wavelengths or colors in the rainbow.

What is an absorption spectrum?

A pattern of dark lines - missing colors - superimposed upon the continuous spectrum from a source. These wavelengths have been absorbed by specific gases.

What is an emission spectrum?

A pattern of bright lines emitted by specific gases releasing energy.

What categorizes atoms into elements?

The number of protons at their nucleus.

What categorizes isotopes of an element?

The number of neutrons at their nucleus.

What is the ratio of protons to electrons in an atom?

1:1

What causes electrons circling the nucleus at a given orbit to jump to a higher orbit?

The absorption of passing energy in the form of electromagnetic waves.

What causes electrons circling the nucleus at a given orbit to jump to a lower orbit?

Atoms naturally de-excite, returning to a ground state and emitting a certain amount of energy.

What is ionization?

When enough energy has been absorbed, an electron can be removed from an atom.

What is ionization energy?

The energy necessary to remove the first electron at ground state from an atom.

What happens to free electrons and ions?

Ions have a net positive charge until they regain the correct number of electrons, releasing a one or more photons in the process.

What is the Doppler Effect

The wavelength of light and sound waves is shorter when the source is approaching you and longer when the approach is receding.

What is radial velocity?

A motion toward or away from the observer.

What is redshift?

A slight shift to a redder color due to longer wavelengths from a receding object.

What is blueshift?

A slight shift to a bluer color due to shorter wavelengths from an approaching object.

Why does the Doppler Effect not alter how astronomers identify the elements of a celestial body?

Astronomers are paying more attention to the pattern of the bands (location) rather than color.

What is the eyepiece of a telescope?

A tool allowing the viewer to look at an object and change its magnification.

What is a refracting telescope?

magnifies and image by passing light through a perfect piece of glass?

Why are refracting telescopes mostly impractical?

It's challenging to create large pieces of perfect glass, and it sags in the middle and needs correction.

What is a reflecting telescope?

Reflects life off of at least one concave mirror and into the eye of the viewer.

What are qualities of a good observing site?

Clear weather, low humidity, far from light pollution, least amount of turbulent air possible.

What is "seeing?"

The clarity of stars observable from a given point.

What is resolution?

Degree of clarity in an image, measured in arc seconds.

What are charge-coupled devices?

Technology that allows photons in radiation to generate a stream of electrons that are counted at the end of an exposure to create an image from a telescope.

What is a constraint of infrared telescopes?

Astronomers receive more infrared from the telescope's surroundings than what it captures.

How do astronomers block out unwanted infrared in their telescopes?

Telescopes are kept in liquid helium.