THE SOUTHWORTH PLANETARIUM
207-780-4249   www.usm.maine.edu/planet
70 Falmouth Street   Portland, Maine 04103
43.6667° N                   70.2667° W 
Altitude:  10 feet below sea level
Founded January 1970
Julian Date: 245956.16
2019-2020:  CXXVIII

THE DAILY ASTRONOMER
Friday, April 17, 2020
Remote Planetarium 15:   Week 3  Quiz

We're ending Week 3 of the Remote Planetarium on-line course.   Thank you for your helpful feedback and positive comments.   We certainly hope you're continuing to enjoy these classes.     Please send us any questions and comments you would like to share!  Our apologies if we don't respond straight away.

Thank you also to subscriber AD who asked us to re post the questions in the answer section.  We should have done that from the beginning.  We're doing it now.

See you on Monday!


1.  Which of the following is NOT a terrestrial planet?
a. Earth
b. Mercury
c. Saturn
d. Mars

2. Which planet is the hottest?
a.  Mercury
b. Venus
c. Earth
d. Pluto

3.  Which planet is surrounded by the greatest number of known moons?
a.  Mars
b. Jupiter
c. Saturn
d. Neptune

4.  If you went to the planet ___________ you could visit _______________,
the highest mountain in the solar system.
a. Mars;  Verona Rupes
b. Venus; Skadi Mons
c.  Mars; Olympus Mons
d. Mercury;  Caloris Montes

5.  _____________ was the most distant planet known to antiquity.
a. Jupiter
b. Saturn
c. Uranus
d. Neptune

6. If an inferior planet is at its greatest western elongation, where will it be visible?
a.  the eastern pre-dawn sky
b.  the western evening sky
c.  the eastern western sky
d.  it won't be visible at all

7.  After Venus passes through inferior conjunction, where would you expect to find it in our sky?
a.  the western evening sky
b.  the eastern predawn sky
c.  rising at sunrise
d.  none of the above

8.  Jupiter was last at opposition on June 10, 2019.    When should it be at opposition again?
a.  July 14, 2020
b.  August 31, 2020
c.  January 9, 2021
d.  September 1, 2021

9.  One can find Venus in the western evening sky.    Based on this one piece of information, what conclusions can we draw?
a.  the next time Venus is in conjunction with the Sun, it will be between the Sun and Earth
b.  the next time Venus is in conjunction with the Sun, it will be on the far side of the Sun relative to Earth
c.  Venus will be closest to Earth now
d.  One can draw no conclusions from that one piece of information.

10. How many times a year will Mercury generally be in inferior conjunction?
a. once
b. twice
c.  three times
d.  five times

11. Force equals mass times ____________
a. volume
b. velocity
c.  acceleration
d.  momentum 

12.  How can the Voyager 1 spacecraft continue to travel at a speed of more than 35,000 miles per hour?
a.  the craft contains an ion propulsion drive
b.  the craft's speed is maintained by the radioisotopic thermalelectric generator
c.  it is moving at this speed because it is traveling on its own volition through the vacuum of outer space
d. it expels gases in one direction which propels it in the opposite direction

13.  Let's say you had two asteroids separated by one million miles.    If you reduce their separation distance to half a million miles, their mutual gravitational attraction ______________
a.  doubles
b.  becomes four times greater
c.  is reduced by half
d.  remains unchanged

14.  The range of gravity is _________________
a. infinite
b.  limited to the boundaries of the object's host galaxy
c.  limited to 100 light years
d.  limited to a distance equal to 11,314 times the radius of the massive object

15.  The "Fundamental Theorem of Astrophysics" states that
a.  the chemical composition of stars is unknowable
b.  the laws of physics governing Earth are applicable throughout the Universe
c.  the Big Bang cannot be precisely modeled
d.  other Universes must exist

16.  What is the Sun's right ascension on the first day of spring (northern hemisphere)?
a. 0 hours
b. 6 hours
c. 12 hours
d.  18 hours

17. The declination of Regulus, the brightest star in Leo the Lion, is almost +12 degrees.  Which of the following statements about Regulus is/are true
a. it is visible everywhere in the northern hemisphere
b. it is directly overhead for observers at latitude 12 degrees N
c. it isn't visible to observers south of 78 degrees S latitude
d. it is circumpolar above latitude 78 degrees N

18.  What will the Celestial Equator's maximum height be for an observer at 60 degrees N?
a.  60 degrees
b.  45 degrees
c. 30 degrees
d.  15 degrees

19.  Alpha Centauri's declination is approximately -60 degrees.   Can we see it here in Portland (ME)?
a.  no
b. yes
c.  yes, but only in the autumn
d.  yes but only in the spring and winter

20.  Sirius' declination is - 17.  Which of the following statements about Sirius is/are true?
a.  it is visible everywhere in the northern hemisphere
b. it passes directly overhead at latitude 17 degrees S
c. it is only visible in the summer
d. it is circumpolar at the South Pole

ANSWERS

1 Which of the following is NOT a terrestrial planet? 
c. Saturn
A terrestrial planet is comparatively small, dense and is enshrouded in a thin atmosphere.   A gas giant or Jovian planet is large, consists largely of lighter elements and has thick atmospheres.   Saturn is a Jovian planet.    The others are terrestrial.
Review
TERRESTRIALS
Mercury, Venus, Earth and Mars
JOVIANS
Jupiter, Saturn, Uranus and Neptune

2. Which planet is the hottest? 
b. Venus 
 Surprise!   Yes, even though Mercury is millions of miles closer to the Sun than Venus, the second planet is still the hottest.   Although Mercury is much closer, it lacks any atmosphere.  Venus is covered by a thick atmosphere consisting of the greenhouse gas carbon dioxide.    Whereas Mercury's daytime surface temperature averages 700 degrees, Venus' temperature slightly exceeds 900 degrees F.

3.  Which planet is surrounded by the greatest number of known moons? 
  b. Jupiter 
As of now, astronomers have detected 79 known moons around Jupiter.     The following is a list of each planet and the number of known moons 
MERCURY - 0
VENUS - 0
EARTH - 1
MARS - 2
JUPITER - 79
SATURN -  76
URANUS -  27
NEPTUNE - 14
PLUTO -  5
 
4. .  If you went to the planet ___________ you could visit _______________,
the highest mountain in the solar system.
  c.  Mars; Olympus Mons  
Mars might be smaller than Earth, but it contains some of the solar system's largest structures.   Olympus Mons' summit is 72,000 feet above the Martian surface and its base is as large as Missouri.       Its immense canyon system, the Valles Marineris, extends more than 2500 miles!

5.  _____________ was the most distant planet known to antiquity.  
b. Saturn 

See below:

ptolemaic.gif
Andrew Borde's "The First Book of the Introduction of Knowledge (1542)" includes this detailed diagram depicting the Ptolemaic Universe.   Earth occupies the center and Saturn the seventh circle.  No other planets are listed as none were known at the time.   

William Herschel discovered Uranus in 1781.

John Couch Adams and Urbain Leverrier independently discovered Neptune in 1846.
[Credit is sometimes extended to Johann Galle who used Leverrier's predictions to find Neptune in his telescope.  He and his assistant, Heinrich d'Arrest, were the first to observe Neptune telescopically.  Adams and Leverrier determined its approximate location mathematically.]

Clyde Tombaugh discovered Pluto in 1930.

6. If an inferior planet is at its greatest western elongation, where will it be visible? 
  a.  the eastern pre-dawn sky  
  • when a planet is at greatest western elongation, it will be visible in the eastern predawn sky. 
  • when a planet is at greatest eastern elongation, it will be visible in the western evening sky.

  7.  After Venus passes through inferior conjunction, where would you expect to find it in our sky?  
  b.  the eastern predawn sky  
  1. After inferior conjunction, the planet will move into the predawn eastern sky until reaching greatest western elongation.  
  2. The planet will appear to move back toward the Sun in our sky as it moves toward superior conjunction when it will no longer be visible again.
  3. After superior conjunction, the planet will then move into the western evening sky until it reaches greatest eastern elongation.   It then appears to move back toward the Sun and then vanishes before reaching inferior conjunction again.  
download.png
8.  Jupiter was last at opposition on June 10, 2019.    When should it be at opposition again?  
a. July 14, 2020
Jupiter's average synodic period is 399 days, meaning that Jupiter requires about 399 days to reappear at the same point relative to Earth.   A period of approximately 399 days separates successive oppositions.    As a rule of thumb, one can say that Jupiter will be at opposition about every 13 months and a few days.     
Jupiter's future opposition dates
  • August 19, 2021
  • September 26, 2022
 
9.  One can find Venus in the western evening sky.    Based on this one piece of information, what conclusions can we draw?
 a.  the next time Venus is in conjunction with the Sun, it will be between the Sun and Earth  

  • After superior conjunction, the planet will then move into the western evening sky until it reaches greatest eastern elongation.   It then appears to move back toward the Sun and then vanishes before reaching inferior conjunction again.    

 10. How many times a year will Mercury generally be in inferior conjunction?  
  c.  three times  
Mercury's synodic period is about 116 days, equal to the time period separating successive inferior conjunctions.  We can expect Mercury to pass between the Sun and Earth about three times a year.

11. Force equals mass times ____________ 
  c.  acceleration  
Newton's second law:  F = ma  (F = force; m = mass; a = acceleration)
The amount of force one applies to a massive object determines its acceleration.   Accelerating a light object to a given speed is easier than accelerating a more massive object.  (Example: easier to push a grocery cart than a stretch Hummer.)

  12.  How can the Voyager 1 spacecraft continue to travel at a speed of more than 35,000 miles per hour?  
  c.  it is moving at this speed because it is traveling on its own volition through the vacuum of outer space  
Newton's first law states that "an object remains in a constant state of motion unless acted upon by an external force."     The Voyager 1 craft is moving on its own volition through the vacuum of outer space.   Because nothing is impeding the Voyager 1 spacecraft it can maintain its motion indefinitely.   

13.  Let's say you had two asteroids separated by one million miles.    If you reduce their separation distance to half a million miles, their mutual gravitational attraction ______________  
  b.  becomes four times greater  
The Universal Law of Gravitation states that the gravitational attraction between two massive objects is proportional to both and inversely proportional to the square of their separation distance.    If you double the separation distance between two massive objects, the gravitational force between them is reduced to one quarter of its original value. If you halve the distance, the force increases to four times its original value.      

14.  The range of gravity is _________________  
  a. infinite  
Gravity has an infinite range.   The Andromeda Galaxy and even all the stars in the Capricornus Supercluster are all exerting their gravitational influence on us.   Of course, as gravity falls off with the square of the distance, this influence is negligible.  

15.  The "Fundamental Theorem of Astrophysics" states that
 b.  the laws of physics governing Earth are applicable throughout the Universe 
Astrophysics is only possible because remote physical objects are governed by the same physical principles that govern objects in our local neighborhood.    

16.  What is the Sun's right ascension on the first day of spring (northern hemisphere)?  
  a. 0 hours 
Right ascension is the celestial equivalent of longitude.    It measures a celestial object's angular distance from the vernal equinox, the intersection point between the ecliptic and celestial equator on the first day of spring.      The scale extends from 0 hours to 24 hours, both of which specify the vernal equinox.
  • On the first day of spring, the Sun's right ascension is 0 hours
  • On the first day of summer, the Sun's right ascension is 6 hours
  • On the first day of autumn, the Sun's right ascension is 12 hours
  • On the first day of winter, the Sun's right ascension is 18 hours
 17. The declination of Regulus, the brightest star in Leo the Lion, is almost +12 degrees.  Which of the following statements about Regulus is/are true
They are all true:
a. it is visible everywhere in the northern hemisphere
[Any celestial object north of the celestial equator is visible everywhere in the northern hemisphere.]
b. it is directly overhead for observers at latitude 12 degrees N
[A star's declination is equal to the latitude at which that star can pass through the zenith, the point directly overhead.    Regulus' declination is 12 degrees and so will occupy the zenith at 12 degrees N latitude]
c. it isn't visible to observers south of 78 degrees S latitude
[To determine a star's visibility region, subtract its declination from 90 degrees.
90 - 12 = 78.    As Regulus is located north of the celestial equator, it will be visible anywhere north of 78 degrees S latitude.]
d. it is circumpolar above latitude 78 degrees N
[If  you know a star's visibility region, you can also know the star's circumpolarity region.  Regulus isn't visible south of 78 degrees S, so it will be circumpolar anywhere north of 78 degrees N.]

18.  What will the Celestial Equator's maximum height be for an observer at 60 degrees N?  
  c. 30 degrees  
From the perspective of a northern hemisphere observer, the Celestial Equator attains its maximum height due south.  That height equals 90 - observer's latitude.    For an observer at 60 degrees N, the Celestial Equator's angle is 30 degrees.  

19.  Alpha Centauri's declination is approximately -60 degrees.   Can we see it here in Portland (ME)?  
a. no
Alpha Centauri cannot be seen north of 30 degrees N.   
We can calculate its visibility region by subtracting 60 from 90.
90 - 60 = 30
As Alpha Centauri is south of the celestial equator, it is visible everywhere in the southern hemisphere.  It will also be visible south of 30 degrees N latitude.    
  • Note: Alpha Centauri will be very difficult to observe at 30 degrees N as it will be so low along the horizon.     
  • Note:  The atmospheric refraction causes objects on the horizon to be elevated by about half a degree.  So, Alpha Centauri would be visible slightly north of 30 degrees N. However, for the sake of simplicity, we're ignoring the atmosphere
20.  Sirius' declination is - 17.  Which of the following statements about Sirius is/are true?  
b. it passes directly overhead at latitude 17 degrees S
[The star's declination is equal to the latitude at which it passes through the zenith.
-17 declination  =  passes through the zenith at 17 degrees S latitude]
d. it is circumpolar at the South Pole
[Every celestial object south of the celestial equator is visible everywhere in the southern hemisphere.  Every celestial object visible in the southern hemisphere is circumpolar at the South Pole.]

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