We return to the classroom on Fridays and so, unlike the rest of the week,
are Earthbound today.   Consequently, we are beneath the mythological
realm.  We'll ascend back through the celestial sphere Monday through
Thursday when we'll encounter the Olympians and their cohorts again.

THE SOUTHWORTH PLANETARIUM
207-780-4249   www.usm.maine.edu/planet
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Altitude:  10 feet below sea level
Founded January 1970
Julian Date: 245950.16
2019-2020:  CXXIV

THE DAILY ASTRONOMER
Friday, April 10, 2020
Remote Planetarium 10:   Week 2  Quiz


1.  Does the moon rotate?
a. No!
b. Yes, but it rotates once every 10 years so it appears not to rotate
c.  Yes, but its rotation rate equals its revolution rate so that it always
keeps its same face toward Earth
d. Astronomers haven't yet managed to determine if the moon rotates or not.

2.  The moon appears to move how much every day?
a.  half a degree
b. two degrees
c. four degrees
d. ten degrees

3.  What is a "Supermoon?"
a.  the waxing crescent moon when it is on the horizon in such a way as to
appear like an "S."
b.  the full moon at or near perigee
c.  the new moon at apogee
d.  the second full moon of the month

4. How much brighter is the full moon than the quarter moon?
a.  twice as bright
b.  four times as bright
c.  six times as bright
d.  nine times as bright

5. The moon's albedo is 0.07.  What does this statement mean?
a. the moon reflects 7% of the sunlight it receives
b. the moon absorbs 7% of the sunlight it receives
c.  the moon's surface gravity is 7% as strong as Earth's
d.  the moon's diameter is 7% that of Earth

6.  Every planetary orbit is a(n) _______________.
a.  circle
b. ellipse
c.  parabola
d. hyperbola

7.  Who devised the three basic planetary laws?
a.  Johannes Kepler
b. Tycho Brahe
c.  Isaac Newton
d.  Copernicus

8. Which of the following statements about planetary motion is/are true?
a.  the closer a planet is to the Sun the greater its orbital velocity
b.  the closer a planet is to the Sun the greater its mass
c.  the closer a planet is to the Sun the shorter its orbital period
d.  the closer a planet is to the Sun the brighter the planet will be

9. What can we determine if we know a planet's orbital period?
a.  the planet's mass
b.  the planet's distance
c.  the planet's brightness
d.  none of the above

10.  What is an "astronomical unit?"
a.  a unit of measurement equal to Earth's average distance from the Sun
b.  a unit of measurement equal to Earth's mass
c.  a unit of measurement equal to the Sun's diameter
d.  a unit of measurement equal to the moon's average distance from Earth

11.   What is the term for a tide that occurs when the moon is new or full
when the moon is at or near perigee when Earth is at or near perihelion?
a.  Spring tide
b.  Neap tide
c.  King tide
d.  Poseidon's tide

12.  If the distance between any two massive objects is doubled, the
magnitude of the gravitational force between them ___________.
a.  doubles
b. remains the same
c.  is halved
d.  is reduced to one quarter of its original value

13. On most days how many tides do we experience each day?
a.  two high tides; two low tides
b. one high tide; one low tide
c  two high tides; one low tide
d. one high tide;  two low tides

14.  Where on Earth could one see the Sun pass directly overhead?
a.  north of the Arctic Circle
b.  south of the Antarctic Circle
c.  within the tropics
d.  nowhere

15. Where on Earth would one see the Sun directly overhead on the June
Solstice?
a.  on the equator
b.  on the Tropic of Cancer
c.  on the Tropic of Capricorn
d.  none of the above

16.   What is an "inferior planet?"
a. a planet that is closer to the Sun than Earth
b. a planet that is farther from the Sun than Earth
c.  a planet that is less massive than Earth
d.  a planet that has fewer moons than Earth

17.  Which one of the following planets cannot be at opposition?
a.  Mars
b.  Venus
c.   Neptune
d.  Saturn

18.   If a planet is at opposition, which of the following statements about
that planet is/are true?
a.  it is a superior planet
b.  it will be at or near its brightest
c.  it will be at or near its closest point to Earth
d.  it is an inferior planet

19.  How does one distinguish between a star and planet in the night sky?
(Could be more than one answer.)
a.  planets generally won't appear to "twinkle."
b.  planets will move with respect to the stars
c.  planets will always be brighter than the stars
d.  planets always appear reddish

20.  Which of the following planets can be in superior conjunction? (Could
be more than one answer.)
a. Mercury
b.  Venus
c.   Mars
d.  Jupiter
e.  Saturn
f.  Uranus
g.  Neptune
h.  Pluto

ANSWERS

1. c.  Yes, but its rotation rate equals its revolution rate so that it
always keeps its same face toward Earth
 ["Synchronous rotation" refers to the equivalence of an orbiting body's
rotation and revolution periods.    The moon completes one rotation and one
revolution in 27.5 days.]

2.  a.  half a degree
[The moon's angular diameter of half a degree is equal to that of the Sun.
For this reason we will occasionally experience total solar eclipses, when
the moon completely blocks the Sun.     They appear to be similarly sized
due to the ratio of their sizes and distances. Although the moon's diameter
is about 400 times smaller than the Sun's, the moon is 400 times closer to
us than our parent star.]

3. b.  the full moon at or near perigee
[Perigee is the closest point in the moon's orbit.    A period of 27.55
days separates successive perigees.   A period of 29.5 days separates
successive full moons.   A super moon occurs when the moon is full around
the time of perigee.  The super moon is 14% larger and 30% brighter than a
micro moon, the full moon that occurs when the moon is at or near apogee,
its most distant point.]

4. d.  nine times as bright
[The moon reflects most of the sunlight it receives directly back toward
the Sun.   As we can see in the graphic below, Earth is within this pathway
when the moon is full.   When the moon is at first or last quarter, Earth
is parallel to that pathway.      The full moon is much brighter than the
quarter moon as a result.]

[image: moon_phases_diagram.jpg]

5. a. the moon reflects 7% of the sunlight it receives
[Albedo measures the ratio of light a body reflects to the light it
receives.   A body with an albedo of 1 reflects all incoming light.  A body
with an albedo of 0 absorbs it all.  We should note that the albedo is
averaged over the entire celestial body.    Some regions reflect more light
than others.    Over all the moon reflects only seven percent of the
sunlight it receives.]

6. b. ellipse
[Johannes Kepler (1571-1630) was the first to assert that planetary orbits
were elliptical, not circular.   Ellipses are closed curves in which the
sum of the distances between the two foci and any point on the ellipse is
constant.

[image: images.png]
In other words, let's imagine you stood at the focus F1 above.   You are
required to walk in a straight line from F1 to any point on the ellipse and
then back in a straight line to the other focus F2.    Your task is to
determine which path is the shortest.  The problem is that all straight
line paths connecting F1 to any point on the ellipse and then back to F2
will be equal.  Kepler's first law tells us that every planet's orbit is an
ellipse with the Sun occupying one focus. ]

7. a.  Johannes Kepler
 [Johannes Kepler was a German mathematician/mystic who devised the three
planetary laws based on his analysis of Tycho Brahe's extensive records of
Mars' changing position in the sky.]

8.
a.  the closer a planet is to the Sun the greater its orbital velocity
c.  the closer a planet is to the Sun the shorter its orbital period
[Kepler's second law states that a planet sweeps out equal areas in equal
time intervals.   This statement means that the closer a planet is to the
Sun the faster it moves.    The orbital paths of the closer planets are
shorter, as well just as a consequence of distance from the Sun.]

9. b.  the planet's distance
[Kepler's third law, the "Harmonic law" relates a planet's orbital period
with its average distance.     It states that the square of a planet's
period is equal to the cube of its semi-major axis.  The semi major axis is
equal to the planet's average distance from the Sun.      Technically, when
one knows a planet's orbital period, one will know its distance as a ratio
to Earth's distance.    For instance, Jupiter's mean distance is 5.2 times
that of our planet.    Kepler's laws didn't tell us the absolute distance
between the Sun and the planets.  That determination was made much
later....we'll discuss this matter in greater detail in a future class.]

10. a.  a unit of measurement equal to Earth's average distance from the
Sun
[An astronomical unit equals Earth's average distance from the Sun, equal
to approximately 93 million miles.]

11.  d.  Poseidon's tide
[The highest possible tides occur when the moon is close to Earth when new
or full at the time when Earth is at or close to perihelion.  Spring tides
occur when the moon is new or full and is working along the same direction
as the Sun.   Neap tides occur when the moon is at first and last quarter
and working in a direction perpendicular to that of the moon.    We
remember that the Sun's influence on the tides is about 44% that of the
moon's.  A King Tide occurs when the moon is new or full when it is at or
near perigee during the time when Earth is not near perihelion.]

12. d.  is reduced to one quarter of its original value
[Isaac Newton actually said

[image: screenshot1.png]
*"The magnitude of the gravitational force exerted between two massive
objects is proportional to both and inversely proportional to the square of
their separation distance."*
If we double the distance between two massive objects, the gravitational
force between them is reduced to one quarter of its original value.   If we
triple the distance between two massive objects, the gravitational force
between them is reduced to one-ninth its original value. ]

13. a.  two high tides; two low tides
 [A high tide will occur at your location when the moon is along the
meridian and at the antemeridian, the polar opposite point.  Low tides
occur at your location when you are at right angles from the moon.  See
graphic below:

[image: WPbGj.jpg]


14.  c.  within the tropics
The Sun can only pass overhead between the Tropic of Cancer (23.5 degrees
north) and Tropic of Capricorn (23.5 degrees south).  The Sun's maximum
altitude outside the tropics  depends on the observer's latitude.    Here
in Portland (ME) the Sun's maximum altitude is 70.5 degrees, which it
attains when crossing the meridian on the June solstice.]

15. b.  on the Tropic of Cancer
[The Sun passes overhead at the Tropic of Cancer on the June Solstice.  The
Sun passes directly overhead along the equator on the vernal and autumnal
equinoxes.  It passes directly over along the Tropic of Capricorn on the
December solstice.]

16. a. a planet that is closer to the Sun than Earth
[From Venus'' perspective, only Mercury is inferior.   From Mars'
perspective, Mercury, Venus and Earth are inferior.      It is all a matter
of location.]

17.  b.  Venus

[image: opposition.gif]
[An inferior planet can never move to the far side of Earth relative to the
Sun as we see in this image.  Only the superior planets can ever be at
opposition.  As Mercury and Venus are both inferior planets, neither can
ever be at opposition. ]

18.
a.  it is a superior planet
b.  it will be at or near its brightest
c.  it will be at or near its closest point to Earth
[Only superior planets can be at opposition.   When a superior planet is at
opposition, it will be at or near its closest point to Earth and therefore
will be at its brightest.]
19.
a.  planets generally won't appear to "twinkle."
b.  planets will move with respect to the stars
[Stars scintillate because they appear as pinpoint light sources.   Planets
are disc-like in appearance and don't generally twinkle unless they are
close to the horizon.     Over the course of many nights, planets appear to
move against the backdrop of stars.  The word "planet," derives from the
Greek word "planetes," meaning wanderer.]

20
a. Mercury
b.  Venus
c.   Mars
d.  Jupiter
e.  Saturn
f.  Uranus
g.  Neptune
h.  Pluto
[All the other planets, even the inferiors, can be in superior conjunction,
on the other side of the Sun relative to Earth.  The graphic below shows us
that inferior and superior planets can move into superior conjunction.
However, only inferior planets can ever be in inferior conjunction.

[image: download.jpg]



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