AST-1002 Exam# 1 Review

•Exam is Tuesday February 11th at 10:40AM. Location: Pugh 170

• Duration of exam is 50 minutes

•Bring Gator 1 ID card

•Bring pencil #2 (HB) with eraser. We provide the scantrons

•No use of calculator or any electronic device during the exam

• Equations will be projected on the screen

•You can use the exam pages as scrap paper if you need to do calculations

•The score will be published in the class web site:

https://www.astro.ufl.edu/~freyes/classes/ast1002/index.htm

• Keep the first page of the exam. Scores will be published using the exam number

• The exam has 30 questions, 5 possible answers, only one valid answer. Duration: 50 minutes

• Exam will include material from Ch0, Ch1, Ch2 and Ch3.

Chapter 0 – Charting the Heavens

Topics •Looking back in distance, looking back in time

•Definition of AU and light-year

•The celestial sphere

•The celestial equator, celestial poles, the ecliptic. Solstices and equinoxes

•The celestial coordinates: Right Ascension and Declination

•Reference (or origin) of Declination. Reference for Right Ascension

• Values and sign of Declination for North and South celestial hemispheres

•The constellations: what are constellations? How many constellations are recognized

by the IAU? Relative distances of stars in a constellation. The origin of the names in the

constellation.

•Reference object or points to define Solar and Sidereal days and the duration of these

two days

•Understand the reason for the seasons: The 23.5 degrees tilt of the Earth’s rotational

axis

• The lunar phases and the relative positions of Sun, Moon and Earth for different

phases of the Moon

• Solar and lunar eclipses: Relative positions of Earth-Moon-Sun and phases of the

Moon

• The effect in the eclipses of the 5 degree tilt of the Moon orbital plane respect to the

Earth orbital plane .

• What is precession?

• What is parallax?

Chapter 0 – Charting the Heavens

Questions

• If a star has a Declination of +40 degrees, in which celestial hemisphere is it located and how far the

celestial equator?

•What are the names of the two points in the celestial sphere where the Sun crosses the celestial

equator?

• Declination of the Sun for summer and winter solstice? Declination of the Sun for the equinoxes?

•What is the relative location of the Moon, Sun and Earth for the different phases of the Moon?

•Where is the Sun respect to the Moon when it is full Moon. Where is the Sun when it is new Moon?

•Where is the Moon respect to the Sun’s position for a lunar eclipse? For a solar eclipse?

•Why we don’t see a solar or lunar eclipse every month?

•Why there are annular solar eclipses?

•What causes the seasons? Is it the changing distance of the Earth to the Sun? Do we have winter or

summer in the north and southern hemisphere at the same time? Is it the tilt of the Earth rotational

axis?

• What is the value of the tilt angle of the rotational axis of the Earth respect to the perpendicular to

the orbital plane?

•What is Earth’s precession? What causes the Earth’s precession?

•What is the effect of the precession in the position of the star Polaris in the celestial sphere?

•What is the duration of the precession cycle?

•What is parallax and stellar parallax?

•How can we use stellar parallax to calculate distance to a nearby star?

Chapter 1 – The Copernican revolution

Topics

• The contributions of Ptolemy, Copernicus, Brahe, Kepler and Galileo to Astronomy

• The 3 Kepler ‘s laws of planetary motion:

1st Law: Planets orbit the Sun in elliptical orbits

2nd Law: The line connecting a planet with the Sun sweep equal areas in equal times

How is the velocity of a planet when is close to the Sun? And how the velocity change if it is

farther from the Sun?

3rd Law: p² = a³. Modified 3rd law by Newton: p² = a³/M

•The ellipse. Eccentricity of an ellipse: distance between the foci divided by the length of the semi

major axis

• Newton’s three laws of motion and his Universal Law of Gravitation

•Galileo observations with his telescope

•Deferent and epicycles in the geocentric model

Questions:

• How was retrograde motion explained in the geocentric model?

•How do we explain the retrograde motion of Mars under the heliocentric model?

• What was Tyco Brahe contribution to astronomy?

•Which are the 3 Newton’s law a motion? F= m · a

•Newton law of Gravitation. How the gravitational force between two masses changes if we

change one of the masses? How does it change if we change the distance? F = G · (m₁ · m₂)/ r² •Galileo’s four important discoveries with his telescope and how some of them supported the

heliocentric model

•Concept of mass and weight. How your mass change if you are on Mars? How is your weight

change is you are on Jupiter?

•How do we determine the value in km of the AU?

Chapter 2– Light and matter

Topics and concepts

• Parameters that describe a wave :Wavelength, amplitude, wave period, frequency

•Velocity of light: c

•The black body. The shape of the blackbody radiation curve

•The kinetic energy of the molecules or atoms: Proportional to the velocity squared (Ek = 1/2mv²).

•Temperature is a measure of the velocity (energy) of the particles (atoms and molecules in a gas).

• High temperatures means higher velocities and higher energies of the gas molecules

• The relation between color and temperature in a black body.

•The color of stars and their temperatures

•Thermal radiation, the radiation laws

•Wien’s law (λmax = 0.29/T)

• Stefan’s law (F = T4 )

•The three types of spectrum: continuous, line emission, line absorption

•Kirchhoff ‘s laws of radiation

•Energy levels in an atom (Bohr’s model)

•Electrons jumping between energy levels: The wavelength of the radiation emitted or absorbed

•The energy of a photon (Eph = h f = h c/ )

•Velocity of a photon in vacuum: c

•The Doppler effect: Only if there is radial velocity. No Doppler effect if the velocity is

perpendicular to the line of sight.

• Doppler effect: If the body is receding, red shift; if the body is approaching, blue shift

• Spectroscopy: Splitting light in different wavelengths and extracting information about an object

Chapter 2– Light and matter

Questions

•Considering the color of a star, can you tell which star are cooler and which are hotter and why?

•If we increase (or decrease) the temperature of a body, how is the total radiative flux change?

Use F = T4

•If we increase (or decrease) the temperature of an object what happens to the wavelength of the

maximum or the peak of emission?

Use λmax = 0.29/T

•What does the temperature means regarding thermal energy in a gas?

• Average kinetic energy of a gas proportional to molecular mass and the square of the speed

•What does the temperature measure?

•Is the velocity of propagation of a electromagnetic wave (light) wavelength dependent?

•What is the velocity of propagation of a radio wave? Velocity of propagations of a Gamma ray?

•Which of the two propagate (or travel) faster?

•Energy of a radio photon (or radio wave)

•Energy of a Gamma photon (or Gamma wave)

Use: Eph = h f = h c/

•Which of the two photons has more energy?

• Doppler red-shift and blue shift. What does it tell you about the velocity and the direction a star

or object is moving?

•If a star is coming towards (or away) from observer how are the spectral lines shifted? If the star

is moving perpendicular to the observer how are the spectral lines shifted?

•What can we learn from spectral analysis? Chemical composition, temperature, line-of-sight

velocity, rotations rate, pressure of a gas and the presence of magnetic field (Zeeman effect).

Chapter 3– Telescopes

• Two types of telescopes: Reflectors (mirrors) and refractors (lenses)

•The two important parameters (or characteristics) of a telescope:

- Light Gathering Power (or light collecting area ) (LGP D² )

- Resolution (Angular resolution λ/D ).

Both characteristics depends on the diameter of the telescope

•Light gathering power depends on the square of diameter (collecting area)

•The resolution (angular resolution) of a telescope increases with the diameter

•The resolution is measured in arc second. A small number means better resolution

•The image of a star produced by a telescope has a central bright spot called the Airy disk

•The diameter of the Airy disk increase with decreasing diameter (aperture )

of a telescope

• Small diameter of a telescope, produce a larger Airy disk, bad resolution.

• Large diameter, smaller Airy disk, good angular resolution, better resolution

•Instrumentation attached to telescopes: CCD, spectrographs

• The effect of the terrestrial atmosphere in the formation of an image

•Use of a telescope and attached instruments: Imaging, spectroscopy, photometry,

astrometry, timing

• Advantage of using interferometry

Chapter 3– Telescopes

Questions

• Why astronomers build bigger (large diameter) telescopes?

• Any advantage of having large diameter telescopes?

•What is the objective of a reflecting telescope? Of a refracting telescope?

• What is the focal length of a telescope?

• What is the dependence of the diameter of a telescope with the light gathering power?

•What is the dependence of the diameter and the wavelength with the angular

resolution of a telescope?

•If the separation between two star in a binary system is much smaller that the

resolution of the telescope, will you be able to see those two star separated? Why?

• Can you see the craters on the moon with the naked eye? Why?

• The formula to compute the magnification of a telescope

• Using high magnification, does it improve the resolution of a telescope?

•What happens to a pixel in a CCD when it is hit by photons?

•How a CCD stores an image in a computer?

• Images taking by IR, UV, X-rays or Gamma-ray telescopes can be represented by colors.

What do the colors mean?

•What happen to the image of a star taking by a ground-based telescope when

several short exposure are taking?

Do the stars twinkle? Do planets twinkle? Why?

•What can we learn about an object using spectroscopy?

Which of the following statements does not use the term angular size or angular

distance correctly?

(1) The angular distance between those two bright stars in the sky is about 2 meters.

(2) The angular distance between those two houses in the distance is 10 degrees.

(3) The angular size of the Sun is about the same as that of the Moon.

(4) The angular size of the Moon is about 1/2 degree.

(5) You can use your outstretched hand to estimate angular sizes and angular

distances.

An example of the format and type of questions for the exam

Which of the following statements about the celestial sphere is not true?

(1) When we look in the sky, the stars all appear as though they are located on the

celestial sphere.

(2) The celestial sphere does not exist physically.

(3) The "celestial sphere" is just another name for our universe.

(4) The Earth is placed at the center of the celestial sphere.

(5) From any location on Earth, we can see only half the celestial sphere at any one

time.