Marywood University Department of Mathematics Course Information for Physics 112 by Dr. J.

Phys 112 Introduction to Astronomy

Astronomy is a study of our universe and an effort to answer questions about where we are within that universe. Topics include basic motions of the sun, moon, and planets, the origin of modern astronomy, radiation and telescopes, the structure of our sun, the interaction between light and matter, a tour of the solar system, and properties of stars, black holes, and galaxies. The textbook is "Horizons, Exploring the Universe", 6th edition, written by Michael A. Seeds and published by Brooks/Cole. Marywood owns an excellent 8-in (203 mm) Celestron telescope with a focal length of 2032 mm and of Schmidt-Cassegrain design. It is located on the roof of the Science Building and students will be observing the skies on class nights when the weather is clear. The course grade is determined by 3 tests, weekly quizes, an observing lab (which might include an overnight campout or trip to a planetarium), and a final examination. Extra credit can be earned by going to the NASA Astronomy Picture of the Day and sending me a comment. This website and other useful websites for the course are listed at the end of this page.

The Andromeda Galaxy

Course Outline

Test #1 Questions from Chapters 1-5 of Seeds' Horizons

True or false.

• The Moon is closer to the Earth during a total solar eclipse than during an annular solar eclipse.
• The resolution of a telescope improves as the aperature diameter increases.
• A total solar eclipse can last for several hours at a specific location.
• The handle of the Big Dipper points to the star Arcturus.
• At the time of an equinox, the Sun rises precisely due east and sets due west.
• If you lived on the Moon, Earth would rise and set every 29 days in the sky above wherever you were located.
• When there is a new Moon, it rises with the Sun in the eastern sky at dawn.
• The distance from us to the nearest star Alpha Centauri is about five times the distance to Neptune.
• Each planet achieves its maximum speed in its orbit around the Sun at aphelion.
• A waxing crescent Moon occurs between third quarter Moon and new Moon.
• A lunar eclipse can only occur when there is a full Moon.
• The apparent magnitude of a star depends only on its distance from us.
• Earth is at perihelion on the same day as summer solstice.
• The seasons are primarily the result of the tilt of the Earth's axis to its orbital plane.
• Alpheratz and Polaris are both stars in the constellation Pegasus.
• Betelgeuse and Bellatrix are both stars in the constellation Orion.

Fill in the blank.

• Our Celestar 8 telescope (made by Celestron) has a focal length of 2023 mm. When we use the 25 mm eyepiece, what is the magnification? ____________
• The imaginary line through zenith and the north celestial pole is called the ____________________. When a star transits this line, it is at the __________________ point it will achieve in the sky that night.
• A planet achieves its minimum orbital speed at _______________ .
• The darkest part of the shadow which occurs during an eclipse is known as the ______________ shadow.
• In Ptolemy's planetary model each planet traveled on an _____________ whose center revolved around the Earth. This was supposed to explain the observed backward motion of some planets known as __________________ motion.
• The primary mirror of most reflecting telescopes has the shape of what type of conic section? ____________
• The Almagest was written by _________________.
• When over half of the side of the Moon facing us is illuminated, it is known as a __________________ Moon.
• In the northern hemisphere, the angle of elevation from the horizon to Polaris is the same as the ________________________ of the observer.
• The day of the year when the northern hemisphere receives the least amount of sunlight is known as ______________ ________________. The declination of the Sun on that day is ________ and its right ascension is __________ .
• The orbit of each planet is an __________________ with ________________ at one focus. This is known as _____________________ First Law of Planetary Motion.
• A magnitude &endash;1 star is brighter than a magnitude 3 star by what factor? ___________________
• In a picture of star trails, the angle which the beginning and the end of each trail subtends is 120º. How long did the exposure last?_____________
• Who's detailed and lengthy observation records was Kepler able to acquire which enabled him to form his three laws?__________________
• Our telescope has an aperture of about 200 mm. How much more light is gathered by our telescope than one with an aperture of 50 mm ? ____________
• The Principia was written by _________________.

Multiple Choice.

• The Earth's axis precesses through one complete circle every
  • A. 260,000 yrs B. 365 days C. 24 hrs D. 23.5 yrs E. Not listed
• The day of the year when the northern hemisphere receives the least amount of sunlight is known as:
  • A. summer solstice B. equinox C. aphelion D. zenith E. None of these.
• The pattern of eclipses which repeats itself every 18 years, 11.3 days is known as the _____ cycle.
  • A. Saros B. ecliptic C. epi- D. precessional E. Not Listed
• When a star transits the meridian, it is at the _______ point it will achieve in the sky that night.
  • A. farthest B. dimmest C. lowest D. highest E. None of these.
• The 36-mirror Keck Telescope is located on
  • A. Mauna Kea B. Kitt Peak C. Mount Palomar D. Mount Wilson E. Not Listed
• There would be no change of seasons during the year anywhere if
  • A. the eccentricity of Earth's orbit were 0.
  • B. Earth's axis was perpendicular to the plane of its orbit.
  • C. the Moon revolved around the Earth once every 6 months.
  • D. the mean distance of Earth to the Sun was larger by 10 million miles.
  • E. None of these.
• In Ptolemy's planetary model each planet traveled on a path known as an _________ whose center revolved around Earth.
  • A. ellipse B. epicycle C. deferent D. ecliptic E. None of these.
• A certain Keplerian telescope has a converging objective lens with focal length 700 mm and a converging eyepiece with focal length 20 mm. What is the magnification of the telescope?
  • A. 350 X B. 1400 X C. 35 X D. 14000 X E. Not listed
• The declination of the Sun on the day of the vernal equinox is
  • A. &endash;23.5° B. 0° C. 23.5° D. 90° E. Not listed
• The approximate time between first quarter Moon and full Moon is _______ .
  • A. 1 week B. 1 month C. 3 days D. 15 days E. 24 hours
• A magnitude -1 star is brighter than a magnitude 4 star by what factor?
  • A. 40 B. 6.3 C. 5 D. 2.5 E. None of these.
• Our Celestron telescope has a focal length of about 2100 mm. What focal length eyepiece will produce a magnification of 300X?
  • A. 6300 mm B. 7 cm C. 7 mm D. 6300 cm E. None of these.
• The Celestron has an aperture of 8 inches. This means that 2 objects closer than _____ of arc cannot be resolved by this telescope. (1 inch = 2.54 cm)
  • A. 20.32 cm B. 1.45 minutes C. 1.75 seconds D. 0.57 second
• How much more light can a 50-cm telescope gather than a 10-cm telescope?
  • A. 25 times B. 5 times C. 500 times D. 0.2 times E. None of these.
• The 200-in Hale telescope is the largest telescope in the Western Hemisphere. It is located on
  • A. Kitt Peak B. Mauna Kea C. Mt. Palomar D. Elk Mountain

Short Answer/Computational.

• What body is located at one focus in the elliptical orbit of every planet in our solar system?
• At what point in its orbit does a planet achieve its maximum orbital speed?
• By what factor is a star of magnitude 2 brighter than a star of magnitude 6?
• Why doesn't a lunar or solar eclipse occur every month ?
• On what day does winter solstice occur? What is the declination of the Sun on that day? What is unique about this day in the northern hemisphere?
• Explain what causes a lunar eclipse. Does a total lunar eclipse occur more or less frequently than a total solar eclipse? Why?
• Describe what is meant by precession of the Earth's axis. How long is one precessional period?
• Name two factors concerning the motion of the Earth that can alter the planet's heat balance and may be responsible for the ice ages.
• What do we call the days which occur at the points of intersection of the ecliptic and the celestial equator? What is special about these days? About when do they occur?
• Summer solstice is coming up soon. On what day does it occur? What is the declination of the Sun on that day? What is unique about this day in the northern hemisphere?
• Diagram the Earth-Moon-Sun system as it is during neap tides. Which phases of the Moon occur at this time? Are these tides on Earth more or less extreme than usual?
• Give two reasons why winter days are colder than summer days.
• What did Galileo observe through his telescope that proved that not all celestial objects revolved around the Earth?
• What do we call the days which occur at the points of intersection of the ecliptic and the celestial equator? What is special about these days? About when do they occur?
• Define a sidereal day. Is it longer or shorter than a solar day?
• State Kepler's three laws.
• Sketch a diagram of a Cassegrain telescope labeling the primary and secondary mirrors and sketch the path of a light ray from where it enters the aperture to the eye of the observer.
• Large objective mirrors in reflecting telescopes are very difficult to make. How does the Keck telescope deal with this problem?
• The network of telescopes in New Mexico is known as the VLA. What does VLA stand for and what type of radiation does it receive?
• How big is the primary mirror of the Hubble space Telescope? What is the main advantage that Hubble has over terrestrial telescopes?
• If a planet has an orbital period of 8 years, what is its average distance from the Sun? (Be sure to use the proper units.)
• Compute the distance in kilometers represented by a light-hour. Express your answer in scientific notation. (Round to the nearest hundredth.)
• The planet Pluto has a mean distance of about 6 billion (i.e. 6 x 10⁹) km from the Sun. How long does it take light to travel from the Sun to Pluto?
• The comet Icarus completes one journey around the Sun every 15 months. Determine its mean distance from the Sun in AU. (Be sure to use the right units in your formula.)
• How much brighter is a 2nd-magnitude star than a 7th-magnitude star?
• If you were on the Moon, what would be the angular diameter of Earth in the lunar sky? (Earth's diameter is about 12,800 km. The average distance of the Moon from Earth is about 380,000 km.) Would it look bigger or smaller than the sun?

Test #2 Questions from Chapters 6, 7, 8 of Seeds' Horizons

True/False.

• The Doppler effect is sensitive only to motion along the line of sight (i.e. radial).
• As an object's temperature increases, the radiation wavelength of maximum intensity decreases.
• The temperature of a sunspot is about the same as that of the surrounding photosphere.
• In an H-R diagram, 90% of all stars fall on the main sequence.
• The larger the distance modulus, m - M_v , of a star, the farther away it is from us.
• The chromosphere layer of the sun lies above the photosphere and can only be seen during a total solar eclipse.
• Type O stars are hotter than type M stars.
• If the distance to a star is greater than 10 pc, then its apparent magnitude is less than its absolute magnitude.
• Sunspots usually occur in pairs with opposite magnetic polarity.
• More distant stars have larger parallax angles than closer stars.
• The energy in a photon increases as the wavelength increases.
• Granulation is caused by rising currents of hot gas below the photosphere.
• Solar flares have no known effect on Earth.
• Solar prominences have twisted and looped shapes beacause of the magnetic field.

Multiple Choice

• The absorption lines associated with a particular star split apart and then merge back again a few days later. This method of identification indicates the star to be a _____ binary system.
  • A. Eclipsing B. Spectroscopic C. Astrometric D. Visual
• The surface temperature of Vega is about four times the surface temperature of Antares. How much more flux is emitted by Vega than by Antares?
  • A. 8 times B. 16 times C. 64 times D. 256 times E. Not listed
• The eclipsing binary in the constellation Perseus known as "the winking eye of the demon" is
  • A. Mira B. Deneb C. Algol D. Polaris E. None of these.
• An electron in an atom may move from one orbit to another by absorbing or emitting a photon of the proper energy. Because only certain orbits are permitted, only photons of certain ___ can be involved.
  • A. weights B. wavelengths C. sizes D. speeds E. None of these.
• Dips in brightness recorded in the light curve of a binary system occur when
  • A. our line of sight is is parallel to the orbital plane.
  • B. one star is brighter than the other star.
  • C. our line of sight is is perpendicular to the orbital plane.
  • D. one star is more massive than the other star.
  • E. None of these.
• By studying the Zeeman effect, George Hale discovered strong magnetic fields in
  • A. helium B. the Sun's core C. the corona D. sunspots E. None of these.
• Most of the light we see coming from the sun originates in the
  • chromosphere B. photosphere C. corona D. sunspots E. magnetic field
• A star lies at a distance of 48 pc and has an apparent magnitude of 0.3. What must be the absolute magnitude of this star?
  • A. 8.4 B. -3.1 C. 5.0 D. -1.5 E. None of these.
• Solar activity reaches a maximum every
  • A. 11 months B. 22 months C. 11 years D. 15 years E. None of these.
• Absorption lines of Titanium Oxide are most likely to be found in the spectrum of a star of which of the following spectral types?
  • A. A B. B C. O D. M E. X

Short Answer/Computational

• Algol is a binary star system in the constellation Perseus. Every 69 hours the amount of light received from Algol decreases. What causes this?
• Why did the Hubble Space Telescope increase the number of stars to which we can apply the parallax method to find the distance?
• Describe the method of spectroscopic parallax used to determine the distance to a main sequence star.
• State Wein's law concerning blackbody radiation.
• Explain what causes absorption lines in the spectrum of a star.
• How do absorption lines in the spectrum of a star give us information as to the elemental composition of the star?
• What is the spectral type of the Sun? Rigel and Betelgeuse are stars in the constellation Orion of types B and M respectively. What color do each of these stars appear to us?
• Briefly describe the process at the core of a star that creates its energy.
• Why do we expect absorption lines due to TiO molecules to be weak in the spectra of all but the coolest stars?
• Describe the method for determining the distance to a Cepheid variable star.
• The star Procyon A is a distance of 11.4 light-years away and has an absolute magnitude of M_v = 2.64. What is its apparent magnitude?
• A star is receding from us radially at a speed of 300 km/sec. Radiation emitted by the star at 500 nm will be detected by us at what wavelength?
• In a laboratory the Balmer H_b line has a wavelength of 486.1 nm. If the line appears in a star's spectrum at 486.4 nm, what is the star's radial velocity?
• A transition between two energy levels produces a photon with l = 1200 nm. If a different transition involves 3 times as much energy as the first one, what wavelength photon does it produce?
• A star is receding from us radially at a speed of 300 km/sec. What will be the Doppler shift of an absorption line in the spectrum produced on Earth corresponding to radiation emitted by the star at 500 nm? At what wavelength will that absorption line be detected?
• Deneb has an apparent magnitude of 1.26 and is about 490 pc away. Find its absolute magnitude and parallax angle.
• The Sun played a major role in testing one of the great scientific principles discovered by Albert Einstein. Name this principle and describe the role of the Sun in verifying it.

Test #3 Questions from Chapters 11, 12, 13 of Seeds' Horizons

True/False

• Neutron stars have very weak magnetic fields.
• Our Milky Way galaxy is a spiral galaxy.
• Population I stars are metal rich which implies they are younger than Population II stars.
• Globular clusters tend to be found in the halo of our galaxy.
• Open star clusters contain many more stars than globular clusters.
• The density of a black hole is greater than that of a neutron star.

Multiple Choice

• A neutron star is expected to spin rapidly because
  • A. it has a high density.
  • B. it conserved angular momentum when it collapsed.
  • C. it has such a high temperature.
  • D. the energy from the parent supernova explosion made it spin faster.
  • E. it has a high radial velocity.
• An isolated black hole in space would be difficult to detect because
  • A. there would be no light source nearby.
  • B. it would not be rotating rapidly.
  • C. it would be stationary.
  • D. very little matter would be falling into it.
  • E. it has no neighboring black hole with which to talk.
• Pulsars are believed to slow down because
  • A. they are converting rotational energy into radiation.
  • B. they are dragging companion stars around in their magnetic field.
  • C. of friction with the interstellar medium.
  • D. the conservation of angular momentum.
  • E. their mass is decreasing.
• The _________ theory describes a pulsar as a rotating neutron star with two beams emanating form the magnetic poles of the neutron star.
  • A. Zeeman B. nuclear C. lighthouse D. Hubble E. Einstein
• The _________ of a black hole is the distance from the center at which the escape velocity is equal to the speed of light.
  • A. Schwarzschild radius B. Chandrasekhar limit C. gravitational constant
  • D. singularity E. Babcock number.
• The event horizon of a black hole
  • A. is believed to be a singularity.
  • B. is a crystalline layer.
  • C. has a radius equal to the Schwarzschild radius.
  • D. marks the inner boundary of a planetary nebula.
  • E. is located where synchrotron radiation is created.
• Theory predicts that the mass of a neutron star may not exceed
  • A. 0.4 solar masses B. 1.4 solar masses C. 2 solar masses D. 3 solar masses
• Roughly how far is our solar system believed to be from the center of the Milky Way?
  • A. about 1/3 of the distance from center to edge
  • B. about 2/3 of the distance from center to edge
  • C. about 4/5 of the distance from center to edge
  • D. in the bulge very near the center
  • E. None of these.
• Astronomers believe that the reciprocal of the Hubble constant is a good estimate of
  • A. the age of the universe.
  • B. the velocity of the Milky Way.
  • C. the average radius of most spiral galaxies.
  • D. the amount of gray in Dr. Johnson's hair.
• Astronomers believe the approximate age of our sun to be about
  • A. 50 million years B. 750 million years C. 2 billion years D. 5 billion years E. 20 billion years
• Observation of galaxies indicate that about ________ percent of the universe is dark matter.
  • A. 5 B. 25 C. 50 D. 75 E. 95
• The three main types of galaxies are irregular, spiral, and
  • A. globular B. elliptical C. abnormal D. nuclear E. None of these.
• If a galaxy has a radial velocity of 8000 km/sec and the Hubble constant is 70 km/sec/Mpc, what is the distance to this galaxy?
  • A. 8.75 x 103 Mpc
  • B. 2.5 x 109 Mpc
  • C. 5.6 x 105 Mpc
  • D. 114 Mpc
  • E. 0.0875 Mpc
• A Cepheid variable star can be used to estimate the distance to a galaxy because
  • A. its period is proportional to its age.
  • B. its radial velocity is half of the distance.
  • C. its period can be used to estimate its luminosity.
  • D. a chart exists of the distances to all Cepheid variables.
  • E. Not listed

Short Answer/Computational

• Explain why the upper limit for the mass of a neutron star is about 2 to 3 solar masses.
• What is an accretion disk ?
• What is the Schwarzschild radius of Saturn? (mass = 5.7 x 10²⁶ kg; G = 6.7 x 10^-11 N-m²/kg²)
• Explain the experience of an astronaut as he/she approaches a black hole.
• Describe how we can find the distance to a Cepheid variable star.
• Why do astronomers think that galaxies contain more matter than we can see?
• Pulsars tend to slow down as they age. What phenomenon could cause them to speed up again?

Useful Websites

http://antwrp.gsfc.nasa.gov/apod/astropix.html (The NASA Astronomy Picture of the Day)

http://www2.astronomy.com/astro/ (Astronomy Magazine Homepage)

http://casswww.ucsd.edu/public/tutorial/Distances.html (Astro Tutorial: Parallax, HR-diagram, Hubble)

http://www.lmsal.com/YPOP/Spotlight/Tour/index.html (A Hypermedia Tour of the Sun)

http://www.aspsky.org/ (Astronomical Society of the Pacific Homepage)

http://www.astro.cornell.edu/index.shtml (Cornell University Dept. of Astronomy)

http://www.seds.org/messier/ (Database of all Messier Objects)

Comments to Dr. Craig M. Johnson, Chair, Dept. of Mathematics: johnsonc@ac.marywood.edu

Last update: April 23, 2001

Copyright © 2001 by Marywood University. All rights reserved. Marywood University, 2300 Adams Avenue, Scranton, PA 18509 (717) 348-6211