AST 1002 03Z Intro to Astronomy - Midterm Study Guide

What is "celestial sphere"?

The imaginary sphere on which objects in the sky appear to reside when observed from Earth.

10^8/10^9=?

10^-1

In a system of celestial coordinates that matches latitude and longitude upon Earth, which is the coordinate that is equivalent to latitude?

declination

If there are about 6000 stars in the entire sky that can be seen by the unaided human eye, about how many stars would be seen at a particular instant on a given dark night from a single location with an uninterrupted distant horizon?

3000

Seasonal variations on a planet's surface are caused by ___

the tilt of the planet's spin axis with respect to the perpendicular to its orbital plane.

How long will it take, in solar time, for the Big Dipper to return to the same position in an observer's sky?

23 hrs 56 min

Which of the following statements correctly describes the relationship between stars and constellations?

Every star is located in a constellation.

Only the brighter stars are in constellations.

ts

Only stars close to the ecliptic (Earth's orbital plenel are located in constellations.)

Only those stars that were visible to the ancient Greeks are located in constellations.

Every star is located in a constellation.

In the system of celestial coordinates that matches latitude and longitude on Earth, which is the coordinate that is equivalent to longitude?

Right ascension

In modern astronomy, the constellations are

88 regions of sky, covering the entire sky.

1 arc minute is equal to

1/60 degrees

In angular measurements used in astronomy, the number of degrees in a semicircle is how many times the number of degrees in a right angle?

Two

The direction of Earth's rotation about its axis is the same as the direction of its revolution about the Sun. How does a solar day compare to a sidereal day on Earth?

A solar day is always longer.

Which one of these is not a recent astronomical discovery?

landing a spacecraft on an asteroid

the discovery of life on other planets

the discovery of planets around other stars

sending a spacecraft through Saturn's rings

the discovery of life on other planets

In astronomy, what is the difference between "revolution" and "rotation"?

Revolution refers to motion of one body about another, whereas rotation refers to the motion of one body about its own axis.

The celestial coordinate system of declination and right ascension

can be used to assign coordinates to any direction in the sky.

The average distance from Earth to the Sun, 149,600,000 km, can be written in shorthand notation as

1.496 × 10^8 km

10^2 × 10^5 =

10,000,000

An arc second is a measure of

angle

From any location on Earth, the zenith defines a direction

vertically above the observer

The constellations

are 88 in number and cover the entire sky.

1 arc second is equal to

1/3,600°.

So far as we know, the first person who claimed that natural phenomena could be described by mathematics was

• Aristotle.

• Ptolemy.

• Pythagoras.

• Copernicus.

Pythagoras

The first person to realize that the force holding us onto Earth is the same force that holds the solar system together was apparently

Newton

The intellectual foundation of science is

observation, logic, and skepticism

Which one of the following is not part of the scientific method?

• analyze results

• choose the simplest existing theory

• make an observation or do an experiment

• determine consistence with recognized authorities

Analyze results

In the ancient Greek era, it was almost universally believed that

Earth was the center of the universe

Retrograde motion of a planet refers to which motion, when viewed from Earth?

westward apparent motion with respect to the stars

Which of the following objects does not experience retrograde motion when viewed from Earth?

moon

The Greek mathematician Ptolemy devised a

geocentric model for the solar system.

Nicolas Copernicus was the first person to

develop a comprehensive model for a Sun-centered solar system.

The Copernican system for planetary motions is

Sun-centered, with the planets moving in perfect circles around the Sun.

A planet's sidereal year is different from its synodic year because the

Earth moves

A significant contribution of Kepler to our understanding of the solar system was the

discovery that planetary orbits are not circular.

The phenomenon of parallax is the

change in apparent position of a nearby object compared to background objects as a result of the motion of the observer.

The Danish astronomer Tycho Brahe had a young assistant who became famous himself some time later. His name was

Johannes Kepler

Kepler's first law states that the orbit of a planet about the Sun is a(n)

ellipse with the Sun at one focus

In an ellipse, the major axis is a distance measured

along the longer diameter, passing through the foci of the ellipse

Kepler's second law states that a planet moves fastest when it

is closest to the Sun.

Two of Kepler's laws of planetary motion applied to Earth are that the radius vector from the Sun to Earth sweeps out equal areas in equal times and that Earth's orbit is an ellipse with the Sun at one focus. One consequence of these laws is that the

Earth moves at different orbital speeds at different times of the year.

The simplified version of Kepler's third law of planetary motion relates the period P (in sidereal years) to the length of the semimajor axis a (in astronomical units) in which way?

P^2 = a^3

A light-year is a measure of

distance

When light passes through a prism of glass,

refraction changes the directions of different colors or wavelengths of light.

When white light passes through a prism a spectrum is formed. This is because the prism

causes different wavelengths of light to travel in different directions.

Electromagnetic radiation moving through space with the speed of light consists of oscillating

electric and magnetic fields, always inseparable, always having the same frequency and wavelength and traveling in the same direction.

One nanometer (nm) is

10^-9 m

Visible wavelengths of electromagnetic radiation have a range of wavelengths of

400 nm to 700 nm

All forms of light have what property in common?

they are electromagnetic radiation

The speed of light is

3 x 10^8 m/s

The speed of light in space is

3 × 10^8 meters per second, independent of the speed of the source.

In which of the following parameters does a photon of blue light not differ from a photon of yellow light, in a vacuum?

• wavelength

• speed

• energy

• color

Speed

What is the one fundamental difference between X rays and radio waves?

Their wavelengths are very different

A particular photon has a wavelength of 450 m, and a second one has a wavelength of 580 m. Which of the following statements about the energies of these two photons is true?

The 450-m photon has the higher energy.

Our present understanding of the nature of light is that it

displays behavior of both waves and particles.

Which of the following types of electromagnetic radiation has the longest wavelength?

radio waves

Which of the following types of electromagnetic radiation has the shortest wavelength?

gamma rays

Who developed the first reflecting astronomical telescope?

Isaac Newton

A radio telescope is very similar to a ___ ___ telescope

reflecting optical

Why was adaptive optics developed?

to compensate for image distortion caused by Earth's atmosphere

The detector that in many instances has replaced the photographic plate for astronomical photography is the

CCD (charge-coupled device)

The angle between two adjacent stars whose images can just barely be distinguished by the telescope is a measure of the telescope's

resolution

What is the main reason for using several radio telescopes together as an interferometer?

to obtain much better angular resolution or sharpness in the images

Almost all of the information we have about distant astronomical objects comes from an analysis of

electromagnetic radiation

When a rod of metal is heated intensely, its predominant color will

change from red to orange to white then to blue

To a physicist, a blackbody is defined as an object that

absorbs all radiation that falls on it.

The ratio of the intensities of two different wavelengths in the spectrum of a blackbody depends on the blackbody's

temperature

A typical but very cool star might have a temperature of 3100°C. On the Kelvin scale, this is about

3373 K.

Which one of these temperatures is hottest?

100 K

100°0

100°F

They are all the same

100°C

We plot the intensity of the radiation emitted from an object at a certain temperature versus its wavelength. As we increase the temperature, the wavelength at which the spectrum peaks becomes shorter and shorter. This is an example of

Wien's Law

What is the difference between luminosity and flux?

Luminosity is the rate at which energy is emitted from an entire object; flux is luminosity per unit area.

An example of an object that emits no radiation at all is any

object at a temperature of 0 K.

Why does the Sun look red when it is setting?

Earth's atmosphere scatters shorter wavelength light more easily than longer, so more red light is left to reach our eyes.

Why is the sky blue?

The air molecules scatter blue light better than red light, so more blue light reaches our eyes.

The light from a small amount of a particular chemical element, when heated in a flame, is found to consist of a

pattern of narrow, bright emissions at wavelengths that are specific to the element and different for each element.

The chemical makeup of a star's surface is usually inferred by

spectroscopy of the light emitted by the star.

Spectral lines are of particular importance in astronomy because

each different element has a characteristic line spectrum.

Atoms in a thin, hot gas (such as a neon advertising sign), according to Kirchhoff's laws, emit light at

specific wavelengths or colors in a pattern that depends on the element.

The force that holds the atomic nucleus together is

strong nuclear

The four fundamental forces in nature include all of the following forces except one. Which one is the exception?

• friction

• electromagnetic

• gravitational

• nuclear

Friction

The age of the solar system has been dated rather precisely to 4.56 billion years. What method was used to determine this number?

determining the age of meteorites by radioactive dating

Ionization of an atom occurs when

an electron is removed from the atom.

An atom consists of

protons, neutrons, electrons

The most abundant material in the universe is

Hydrogen

The most common elements in the universe are

hydrogen and helium, with small amounts of heavier elements

Where was all the hydrogen in the universe formed?

in the Big Bang, at the very beginning of the universe

Fusion is the process by which

elements are transformed into heavier elements by nuclear reactions.

The most likely mechanism for the solar system is that the

Sun and planets slowly condensed to their present form from a gas and dust cloud.

The birthplace of the Sun and planets (and of other stars and maybe their planets) is thought to have been in

cool gas and dust clouds.

A gas and dust cloud will not necessarily collapse because it normally experiences a balance between its internal gas pressure and

gravity

Why did the temperature start to rise at the center of the solar nebula?

The nebula was contracting, which increased the speed of the atoms moving in it.

The nebular hypothesis of the formation of the solar system assumes that the material that became the solar system began as a large spherical cloud of gas and dust, rotating slowly. As the solar system formed, most of this material was transformed into a compact, flattened disk, rotating more rapidly. What is the explanation for this change in shape and rate of rotation?

conservation of angular momentum

What force ensured that once the solar system began collapsing it continued to do so?

gravity

The relatively large amount of water found on Earth is believed to have come from

water-rich comets.

The composition of a typical asteroid is

rock and metal

What process had the greatest influence on the features of the Moon durins the first billion years of its existence?

Impacts from space

What is the difference between an asteroid and a meteoroid?

size

What is the basic difference between comets and asteroids?

Comets are mostly composed of ices, whereas asteroids are mainly composed of rocks.

What are the main characteristics of our solar system?

four small planets close to the Sun and four large planets far from the Sun

In our solar system, which of the following planets is not a member of the terrestrial group?

Mercury

Mars

Venus

Jupiter

Jupiter

How do we measure the mass of an extrasolar planet?

We use Newton's law of gravity, using the measured distance of the planet from its star and the planet's gravitational pull on the star

Which planet in our solar system has the largest mass?

Jupiter