PHYS 1301 - Ch. 5 (Learnsmart & Connect)

Match the cycles of the Mayan calendar to their descriptions.

- 260 days : Religious / astronomical period possibly related to Venus. - 365 days : The year used, for example, for planting and harvesting. -400 years : Groups of years for measuring long periods of time. -5000 years : A long count cycle that periodically rolls over (it does not end).

Select all of the properties that describe reflecting telescopes.

- A mirror is the primary collector. - Often the secondary mirror blocks some of the primary.

Select the choices that describe information an astronomer might include in a proposal to use a telescope.

- Analysis of previous researchon the target object. - Information about the specific cameras to be used. - An explanation of what scientific results will be obtained. - An argument why the observation is useful.

Which of the following advantages of a CCD over photographic film?

- CCDs do not need to be changed out for each exposure. - CCDs record a greater percentage of the photons striking them.

The graph shows the offset between the true solar time and the mean solar time. Select the reasons for this.

- Earth's orbit is elliptical. - Earth's axis is tilted compared to the orbital plane.

Select all the reasons for using daylight savings time.

- It allows industrialized countries more hours of daylight when people are awake. - It saves energy that would be used to light homes and businesses.

Select all the choices that describe a mean solar day.

- It is the same as clock time. - It is the average of the apparent solar day over the year. - It defines the 24 hour day. - It is necessary because Earth's speed in its orbit varies.

Select all the descreptions that apply to the solar day.

- It is the time between successive noons. - It is 4 min longer than the sidereal day.

Match the name of the month with its origin in the Roman calendar.

- July : Named for Julius Ceaser. - August : Named for Augustus Ceaser. - May : Named for Maia, eldest of the Pleiades. - September : Named for being the seventh month (at the time). - March : Named for the god of war.

Which parts of Earth receive 24 hours of daylight for part of the year?

- Latitudes below 66.5 degrees S ( the Antarctic Cicle). - Latitudes above 66.5 degrees N (the Arctic Circle).

Which statements accurately describe how CCD works?

- Photons interact with the semiconductor to free electrons in a pixel. - Brightness is determined by the number of electrons in each pixel.

Match the properties to reflecting or refracting telescopes.

- Reflecting: Primary focusing device is a mirror, Easily supported from the back, Typically has a short tube. - Refracting: Primary focusing device is a lens, Long focal length/long tube, Colors focus at different lengths.

Select all the choices that describe the complex Mayan calendar.

- The 260-day and year-long cycles aligned every 52 years. - Thirteenth was a special number in it. - It used a 20-day week. - It had cycles of days and years of various lengths.

Earth's tilt is responsible for which of the following?

- The North Pole experiences daylight for six months. - The Sun appears to move north and south on the celestial sphere (changes declination) over a year.

Why do we have leap years?

- The seasons would get out of step with the calendar if we did not. - Earth does not orbit the Sun in a whole number of days.

Match the items relating to time to their definitions.

- Time zone ---> A range of longitudes that adopt the clock time of the longitude at their conter. - Standard time ---> The common time wth a time zone. - Universal time ---> The time at the prime meridian (longitude zero.). - Daylight savings time ---> An artificial adjustment of standard time that sets it one hour ahead during the summer.

Select all that are common purposes of telescopes.

- To collect more light than the eye collects. - To allow astronomers to see objects in more detail. - To collect nonvisible wavelengths of light from celestial objects.

Match the day of the week (in English and other languages) with the planets and words they are derived from.

- Wednesday : Mercury ; Woden (Germanic god). - Tuesday or Mardi (French) or Martes (Spanish) : Mars ; Mars (Roman god of war). - Thursday or Jueves (Spanish) : Jupiter ; Jove (Roman) or Thor (Germanic). - Saturday : Saturn ; Saturn (Roman god).

Which of the following telescopes would not be suitable for ground-based observations?

- X-ray. - ultraviolet telescope.

Match the approximate lengths of time with the changes in the sky that have been observed by people since ancient times.

- Year ---> Time for the Sun to complete one trip through the zodiac constellations. - Month ---> Time from new moon to the next new moon. - Day ---> Time from noon to the next noon.

When two telescopes are linked together as an interferometer, they are ___________.

- acting as opposite edges of a large telescope. - using interference to improve resolving power.

In contrast to film, CCDs, such as those used in digital cameras, __________.

- can be reused. - record more of the photons that strike them. (CCDs detect about 75% of photons, film about 10%.)

Infrared telescopes, such as the Spitzer Space Telescope, must be placed in space. These telescopes have limited lifetime because they __________.

- constantly use coolant. (Infrared detectors have to be kept cool to reduce electronic noise.) - may be too far away for a repair mission. (Some space telescopes are in orbits far from Earth.)

In addition to directly obtaining their own observations of a specific target from a ground-based observatory, astronomers today might ___________.

- create theoretical models and simulations of galaxy formation with clusters of computers and compare with online archives. - apply for time using a space telescope such as the Hubble Space Telescope or the Chandra X-ray Observatory. - use data from an online archive of a survey, such as observations of thousands of galaxies in the Sloan Digital Sky Survey.

The most common designs for small reflector telescopes are Newtonian and Cassegrain. A Cassegrain telescope has a ____________.

- curved secondary mirror. - hole in the primary mirror.

To minimize atmospheric effects, major observations are built _____________.

- in deserts. - on mountaintops.

A sidreal day _________.

- is the time it takes Earth to turn 360 degrees in space. - is the time it takes a star directly overhead to return to being directly overhead.

The 7-day week was developed independently by several cultures, probably because __________. (Select all that apply).

- it's about 7 days between major phases of the Moon. - the naked eye can see five planets, the Sun, and the Moon change position in the sky.

Which of the following significnt advantages do large reflector telescopes have over large refractors?

- mirrors are less expensive to fabricate than lenses. - mirrors weigh less than the same diameter.

To minimize atmospheric effects, major observatories are built ___________.

- on mountaintops. - in deserts.

False-color images are useful in astronomy to __________.

- overlay different kinds of information on a single image. - represent the energies or wavelengths of non-visible photons. - represent the brightness of non-visible radiation.

Astronomers might create a false-color image to ____________.

- show relative brightness of radio photons. - show surface elevation of a moon. (False color is often used to enhance visibility of features even in optical data.) - show photon energies of an X-ray object. (This image show an X-ray observation with colors assigned by energies.)

The largest optical telescopes in the world are reflecting telescopes, because it is difficult to make a refractor (lens) telescope larger than about 1 meter in diameter. It is difficult because __________.

- the heavy lens distorts under its own weight. - it is very difficult to support large pieces of glass only by the edge. - refracting telescopes have long focal lengths and are very large.

We might expect a culture to have developed a lunar calendar, such as the islamic calendar, rather than a solar calendar, if ________.

- the people lived in a climate with mild seasons. (The Moon cycle is more likely to be important if you don't notice a strong differenece in weather with the seasons.) - nighttime travel (in the days before artificial lighting) was important. (Knowing when the Moon would be full is important if you travel at night without lights!)

Since the local time depends on longitude, solutions in timekeeping that simplify long-distance communication include the creation of _________.

- time zones. - universal time.

Telescopes are placed in orbit __________.

- to observe wavelengths blocked by the atmosphere. - to eliminate atmospheric effects that degrade the image. - so that local weather is not a problem.

What is the smallest separation angle resolvable by a 50-centimeter telescope observing blue light of 500 nanometers?

0.25 arc seconds. (a>0.025 wavelength / D.)

Arrange the statements to explain how adaptive optics are used to improve ground-based telescope observations.

1. A lasser beam is projected into the atmosphere near the target of the observation. 2. The artificial star's image is observed by the telescope. 3. A computer compares the image of what is expected. 4. The telecope primary, and/or secondary mirors are adjsuted by tiny motors are adjusted by tiny motors ti cirrect for the atmospheric distortions. 5. The process is repeated continuously as quickly as possible.

Rank the choices from the most efficient (top) to least efficient (bottom) method of collecting light.

1. CCD. 2. Photographic film. 3. Human eye.

Arrange the step to explain why a solar day is longer than a sidereal day.

1. Start with a star aligned behind the Sun at noon. 2. Earth rotates 360 degrees compared to the star. While doing that, it moves forward along its orbit about 1 degree. 3. The star is once again at "noon", but the Sun is not. 4. Earth has to turn a little bit more to bring the Sun to noon, so the solar day is a little bit longer.

Rank these telescopes according to their ability to collect light, from best (top) to worst (bottomg).

1.) 5.0-meter relfector on Earth's surface. 2.) 3.5-meter reflector in orbit. 3.) 2.5-meter reflector on a mountaintop. 4.) 1.5-meter refractor on a mountaintop. 5.) 0.75-meter refractor on Earth's surface.

Since Earth turns 360 degrees in 24 hours, it turns __________ degrees in 1 hours.

15.

If your new telescope collects nine times more light than your old one, it is _____________ times larger in diameter than your old telescope.

3.

Telescope A's mirror has six times the diameter of telescope B's. How much greater is A's light-gathering power?

36 times.

How many hours does it take for the Sun to move 60 degrees across the sky?

4 hours. (At 15 degrees per hour, this would take 4 hours.)

How much more light will a 10-meter telescope collect than a 5-meter telescope?

4 times as much. (Since the area depends on the square of the diameter cuptures four times as much light.)

To record a visible image of a dim galaxy in the shortest time, which of these telesscopes would be the most choice?

5.0-meter reflecor on Earth's surface.

If it is 6 P.M. in te U.S. central time zone, what time is it in India?

5:30 A.M. (The difference between the time zones is 11.5 hours, and it is later in India, so it is 5:30 A.M. the next day.)

Large optical telescopes built in the early part of the twenty-first century, such as those that comprise the Very Large Telescope show in the figure, individually have mirrors about __________.

8 to 10 meters in diameter. (Keck, the Large Binocular Telescope, the VLT, the Gemini, and the Subaru telescopes are all about this size. The Megallen telescopes are a little smaller, at 6.4 meters.)

Compare the light-gathering power of a telescope with a 10-centimeter (about 4-inch) diameter mirror to that of the human eye. (Take the diameter of the pupil of the eye to be about 6 millimeters.) The light-gathering collecting power of a 10-centimeter reflector is _________ times _________ than that of your eye.

; greater.

Julian calendar

A 12-month calendar devised under the direction of Juliu Ceasar. It includes a leap year every four years.

Based on the diagram, you can conclude that _________.

A solar day is longer than a sidereal day.

Standard time.

A uniform time kept within a given region so that all clocks there agree.

The image shows an electronic detector called a __________ that is the basis of most digital cameras.

CCD. (This shows the structure of a CCD.)

Which of the following is the most commonly used detector system in modern astronomy?

CCDs.

Why does the number of daylight hours change over the course of a year?

Earth's rotation axis is tilted 23.5 degrees from perpendicular to the ecliptic. (If Earth's axis were tilted exactly perpendicular to the ecliptic, all the days would have 12 hours of sunlight.)

The offset between clock time (mean solar time) and sundial time (apparent solar time) is a mostly result of __________.

Earth's varying speed in its elliptical orbit. (When Earth moves faster along the orit, it has to turn more to bring the Sun back to the noon position, so the solar day is longer.)

True or false: The primary purpose of a telescope is to make images of astronomical objects larger (magnify the view).

False. (Actually, the primary purpose of most telescopes is to collect more light from celestial objects, allowing dim objects to be seen in more detail.)

Why does the Sun rise and set?

It appears to move because of Earth's rotation.

____________ years were used to keep the calendar from getting out of step with the seasons.

Leap.

Which of the following disadvantage of reflector telescopes compared to refractors?

None of these choices is correct.

Time zone

One of 24 divisions of the globe, centered at every 15 degrees of longitude. In each zone, a single standard time is kept. Most zones have irregular boundaries.

A __________ day is the length of time it takes for a star directly overhead to return to being directly overhead.

Sidereal.

Which of the following is the most significant advantage of the Hubble Space Telescope (HST) compared to the 4-meter reflectors at the Kitt Peak observatory?

The HST is not affected by atmospheric scintilation

Gregorian calendar

The calendar devised at the request of Pope Gregory XIII and essentially the civil calendar used throughout the world today. It omits the leap year for century years not divisible evenly by 400.

Sidereal day

The length of time from the rising of a star until it next rises. The length of Earth's sidereal day is 23 hours 56 minutes.

Mean Solar Day

The standard 24-hour day. The mean solar day is based on the average day length over a year. (The time interval from solar noon to solar noon varies slightly throughout the year.)

A solar day is _________.

The time between successive noons.

Solar day

The time interval from one sunrise to the next sunrise or from one noon to the next noon. The time interval is not always exactly 24 hours but varies throughout the year. For that reason, we use the mean solar day (which, by definiion, is 24 hours) to keep time.

Universal time

The time kept at Greenwich, England. Universal time is the same as Greenwich mean time. Most local timess (in the continental United States, these are Eastern, Central, Mountain, and Pacific) differ from it by a whole number of hours.

Daylight saving time

The time kept during summer months by setting the clock ahead one hour. This gives more hours of daylight after the workday.

Suppose you were examining a pulsing radio singal from a stellar remnant in a distant part of the Milky Way. Knowing that ionized gas in interstellar space causes dispersion of radio waves, what effect would you expect this to have on the signal?

The time when the pulses arrived would be different for different wavelengths.

___________ time, the time at the prime meridian passing through Greenwich, England, is a 24-hour clock sometimes used to avoid confusion if people working together are at two different longitudes.

Universal.

True or false: The purpose of daylight savings time is to better align the hours of daylight with the time when people are awake and active.

Yes. (The shift realigns daylight hours from the early am to the evening, saving electricity.)

light-gathering power

a measure of the ability of a telescope (or other device) to collect light. It is generally proportional to the are of the telescope's light-gethering power than a telescope with a 3-inch diameter lens.

To maintain a large telescope's primary mirror shape as it is pointed in different directions, ____________.

a segmented mirror is used. (Each segment can be individually adjusted so the entire surface maintains its shape.)

refractor

a telescope that uses a lens to collect and focus light.

The Julian calendar has a leap year every 4 years. The Greogiran system used today removes the leap years from century yers that are not divisible by 400 because ____________.

adding a leap year every 4 years adds a little too much time. (With respect to the seasons tropical year, the year is just 36.24 days, so we are only short 0.96 days every four years.)

Lunisolar calendars, sunch as the Chinese and Jewish calendars, make up for the fact that there is not an even number of Moon phase cycles in an Earth orbital period by __________.

adding a thirteenth month to the year every few years. (About every 3 years, an extra month is added. Consequently, some lunisolar years have more days than others, but the seasons do not get too out of phase with the calendar.)

To use ground based optical telescopes to their theoretical specifications, astronomers must use

adjustable mirrors that can correct for the atmosphere.

Light pollution refers to ______________.

artificial light from inhabited areas being refleted and scattered in the night sky.

A second full moon in any month is referred to as a __________ moon.

blue.

To display data collected by a radio telescope, specific visible __________ are assigned to represent the original intensity range of data in an image.

colors.

A telescope wtih a higher ratio of aperture diameter to observed wavelength of light would _________.

detect finer detail in objects. (The ability to detect fine detail is the resolution. Resolution is determined by the ratio of aperture size to wavelength.)

The size of a telescope's _______________ determines its light-gathering power.

diameter

Which of the following quantities is most crucial in terms of the quality of a telescope?

diameter of mirror/lens.

The number of photons strking a "charge-coupled device" (CCD) is determined by collecting the __________ freed when photons are absorbed by atoms in the semiconductor (usually silicon) layer of the CCD.

electrons.

Astronomers use interferometers to

enhance the resolving power (see fine details) in sources.

A telescope's resolving power measures its ability to see

finer detail in sources.

The actual length of a year is very clsoe to 365.25 days. As a result, we need a leap year once every __________.

four years. (After four years, the calendar would be one full dayout of step without the correction.)

If a CCD records 80% of the photons strinking it, and a photograph 4% how many times larger in diameter would a telescope have to be, to take a photograph equl in sensitiviy to a CCD image in the same amount of time?

four.

To maximize the quality of observations, an observatory with a very large telescope would best be built _______

in a dry area.

Two widely separated telescopes might be linked together as an interferometer to _________.

increase the resolution of observations. (An interometer has a much bigger effective diameter, so it has a high resolution.)

To study a cool dust cloud, an astronomer would have to observe at radio or slightly shorter __________ wavelengths.

infrared.

A mirror designed for visible light would not be suitable to observe X ray wavelengths because the __________.

light would pass through the mirror. (X rays would not reflect off the surface; they would penetrate the mirror and either be absorbed or pass straight though.)

Without time zones, every ____________ could hae its own local (solar) time.

longitude.

One way to increase the resolving power of a telescope is to

make its mirror bigger.

P.M. means __________ ___________, referring to the second half of the Sun's path across the sky each day.

post meridian.

An astronomer is using a telescope that consists of a metal antenna mounted on struts above a 10-meter curved metal dish, mounted outside (no dome). The whole telescope is steerable and can be used during the day or at night. What kind of astronomy is being done?

radio.

A telescope that focuses light by bending light rays through a lens is a ____________ telescope.

refracting.

Quickly moving air cells in the atmoshere affect how much the stars "twinkle"and also make the images of stars somewhat blurred. This amount of blurring is referred to by astronomers as ___________.

seeing.

If its 1 P.M. on the east coast of Brazil, __________ hours will it be 1 P.M. in Alaska.

six.

While looking at a star, you notice it twinkles a lot. This is caused by ___________.

small pockets of warmer and cooler air distorting the image. (This effect is called scintillation and results in poor "seeing".)

An example of a fale color image is shown. A false color image assigns ____________.

specific visible color to photons of nonvisible wavelengths.

The first step an astronomer takes to observe with an observatory's telescope is ___________.

submitting a proposal. (Observing time is assigned based on the proposal.)

Telescope X can resolve two stars separated by no more than 2 seconds of arc. If telescope Y can resolve two stars that are separated by 1 second of arc, then (at the same wavelength) compared to telescope X

telescope Y has at most twice the resolving power.

The seven changing celestial objects were associated with the week in ancient times. The second day of the week goes by "Monday" in English, "lunes" in Spanish, "lundi" in French. It is associated with ____________.

the Moon.

August and July both have 31 days, violating the alternating scheme of 30 and 31, while February has only 28, because ___________.

the ancient Roman calendar was based on politics, not astronomy. (The months named after Julius and Agustus Ceaser needed to have the same length for political reasons. This is also why February is so short, as days were taken from it for political reasons.)

A mean solar day is ________.

the average of the time from noon to noon over all the days of the year.

refraction

the bending of light when it passes through one substance and enters another.

The resolving power of your new telescope is 2 arc seconds. This means that 2 arc seconds is _________.

the minimum angular separation between two stars so they are seen as two stars and not one.

As a result of Earth's axial tilt, the farther north you travel during the summer, _________.

the more hours of daylight.

During an observing session, you find the sky to be clear but the stars are twinkling and the image in your telescope dances around. You might conclude that ___________.

the seeing will make your images look blurry. (The sky will, cause any images you take to have

In an interferometer, the image resolution is set by __________.

the separation of the individual telescopes.

A ruler placed in a glass of water appears bent because __________.

the speed of light changes when light passes from water to air. (The differences in the speed of light in the two materials causes a slight change in the direction of the light waves.)

dispersion

the spreading of light or other electromagnetic radiation into a spectrum. A rainbow is an example of dispersion of light caused by raindrops.

The names of the days of the week are a clue that it may have seven days because __________.

there are objects visible to the naked eye that move across the sky.

The major advantage of space-based telescopes is

they are not affected by atmospheric scintillation.

One important reason to place telescopes in orbit is __________.

to eliminate atmospheric effects that degrade the image.

To correct for the effects of small pockets of warmer and cooler air on light passing throught the atmosphere (scintllatin)

use adaptive optics.

A refracting telescope ___________.

uses a lens to bend light. (Light is refracted (bent) as it passes through the lens.