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: 2459027.16
2019-2020:  CLXX


THE DAILY ASTRONOMER
Friday, July 3, 2020
Remote Planetarium 58:   Week 12 Quiz

Would you believe we have just barely scratched the surface?    Honestly, we would be flattering ourselves to even make that assertion.   To actually do justice to each Remote Planetarium topic, we'd have to post a book, not an article.  Moreover, we would need volumes just to keep everyone apprised of what is discovered every week.   Such is the exponential science of astronomy. Knowing that a long trek still awaits us might exhilarate some and dismay others.    As the adage goes, "The physicist learns more and more about less and less.  The astronomer learned less and less about more and more."    Then again, wouldn't life lose a little of its luster were everything to be precisely amassed and cataloged?

Today's quiz covers the three topics discussed this week: penumbral lunar eclipses, extrinsic variables and Cepheid variables.     The good news about having a truncated week is that we're posting fifteen questions instead of twenty.

1.  One of the lunar eclipses in Saros Cycle 149 will occur on August 17, 2092.    When will the following Saros 149 lunar eclipse happen?
a.  August 17, 2099
b.  August 23, 2101
c.  August 26, 2105
d. August 29, 2110

2.  What is the penumbra?
a.  the outer part of Earth's shadow
b.  the inner part of Earth's shadow
c.  the center of Earth's shadow
d. none of the above

3.  On June 6, 2096, Lunar Saros Cycle 151 will begin.      Based ONLY on information contained within that sentence, which statement(s) do you know must be true?
a.  the eclipse will occur at or around the moon's descending node
b.  the eclipse will be a partial penumbral eclipse
c.  the next Lunar Saros Cycle 151 eclipse will occur around mid-June in 2114.
d.  the eclipse will last four hours

LE2489-04-16T.gif
Questions 4  -5 pertain to the image above.

4.  Observers in Portland, Maine in the year 2489 will see how much of the eclipse that will happen on April 16th?
a.  none of it
b. all of it
c. the eclipse will be in progress when the moon rises
d. the eclipse will be in progress when the moon sets.

5.  Based on information contained within this image, which of the following statement(s) must be true?
a. the next eclipse in this series will occur in late April 2507
b. the next eclipse in this Saros cycle will be of longer duration
c. the zenith Sun position will be at a higher latitude during the next eclipse in this Saros cycle
d. none of the above. 

6.  Which of the following are types of extrinsic variable stars?
a.  rotating variable stars
b. eclipsing binary stars
c. Cepheid variables
d. RR Lyrae variables

7.  An Algol variable is what type of variable star?
a. rotating
b. eclipsing binary
c. Cepheid
d. RR Lyrae 

algol_diagram.png

8.  The image above shows the change in Algol's brightness over time.  This graph is actually called Algol's _________________
a.  light curve
b. magnitude diagram
c.  brightness spectrum
d.  all of the above

9.  Why aren't all binary stars eclipsing binaries?
a. because the star system has to be aligned with Earth in such a way so that the stars block each other during each revolution.
b. all stars are eclipsing binaries from our perspective.  The brightness difference is so slight for most of these that we don't notice them.
c. in order to be an eclipsing binary star, the system has to have an additional component star
d. none of the above.  

10.  Which of the following statements about rotating variable stars is/are true?
a.  their brightness could vary because of darker regions along the photosphere
b.  their brightness could vary because of their ellipsoidal shape
c.  their brightness could vary because of doubly ionized helium in their interiors.
d. none of the above. 

11. Which of the following is/are type(s) of intrinsic variables?
a.  pulsating
b.  rotating
c. cataclysmic 
d. eclipsing binary

12.  How many different types of Cepheid variables have been identified?
a.  1
b.  2
c.  3
d.  4

13.  What mechanism is believed to be responsible for Cepheid variability?
a.  doubly ionized helium
b. core iron reserves
c. dark spots on the photosphere
d. none of the above 

14. Why would a star's brightness change because of pulsations?
a. the change in size and temperature affects the luminosity, or energy output
b. because as the star expands, its mass increases and therefore increases the luminosity
c. as the outer layers contract, the fusion reactions in the core accelerate, increasing the luminosity
d. none of the above. 

15.  The longer a Cepheid's variability period, the _____________ the Cepheid.
a. more luminous
b. less luminous
c. older
d. younger
ANSWERS
  1.  One of the lunar eclipses in Saros Cycle 149 will occur on August 17, 2092.    When will the following Saros 149 lunar eclipse happen?  
  d. August 29, 2110
Eclipses within the same Saros cycle are separated by 18 years 11 days and 8 hours.  
2.  What is the penumbra?
a.  the outer part of Earth's shadow  
Earth's shadow is divided into two regions: the penumbra (outer part) and umbra (inner part).
Lunar_eclipse_chart_close-2038Jul16.png
3.  On June 6, 2096, Lunar Saros Cycle 151 will begin.      Based ONLY on information contained within that sentence, which statement(s) do you know must be true?
a.  the eclipse will occur at or around the moon's descending node
b.  the eclipse will be a partial penumbral eclipse
c.  the next Lunar Saros Cycle 151 eclipse will occur around mid-June in 2114.

Any lunar eclipse that is part of an odd-numbered Saros cycle will occur at or around the moon's descending node.   The first lunar eclipses within any Saros cycle will always be partial penumbral eclipses.  The next eclipse in that cycle occurs on June 18, 2114.  We knew that it would happen in mid June 2114 because successive eclipses within any given Saros cycle are separated by 18 years and 11 days. 

4.  Observers in Portland, Maine in the year 2489 will see how much of the eclipse that will happen on April 16th?
c. the eclipse will be in progress when the moon rises
The moon will be moving into the umbra when the moon rises in Portland, Maine on April 16, 2489.   Observers will not see the moon passing through the penumbra and so won't miss much at all.

5.  Based on information contained within this image, which of the following statement(s) must be true?
a. the next eclipse in this series will occur in late April 2507
b. the next eclipse in this Saros cycle will be of longer duration
c. the zenith Sun position will be at a higher latitude during the next eclipse in this Saros cycle

  • The next eclipse in that series will occur on April 28, 2507.     (18 years, 11 days and 8 hours between successive eclipses within the same Saros cycle.)    
  • The next eclipse will bring the moon along a slightly higher arc.  Its path will bring deeper into Earth's shadow and the eclipse will be of longer duration.
  • Because the next eclipse in the series will occur later in April, the zenith Sun will be at a higher latitude 
6.  Which of the following are types of extrinsic variable stars?
a.  rotating variable stars
b. eclipsing binary stars

Rotating  variable stars and eclipsing binary stars are the only types of extrinsic variables.  Extrinsic variables are defined as stars whose variability is a result of external perspective instead of internal processes.  

7.  An Algol variable is what type of variable star?
b. eclipsing binary
Algol is one of the best known of the eclipsing binary variables.    Algol appears to diminish in brightness whenever the dimmer (secondary) star moves in front of the brighter (primary.) A secondary eclipse occurs when the primary star moves in front of the secondary.  However, that eclipse is barely noticeable. 

8.  The image above shows the change in Algol's brightness over time.  This graph is actually called Algol's _________________
a.  light curve
Every variable star has a corresponding light curve, one that shows how its brightness changes over time.   By studying the light curve, an astronomer can determine the variable star type. 

9.  Why aren't all binary stars eclipsing binaries?
a. because the star system has to be aligned with Earth in such a way so that the stars block each other during each revolution.
More than half of the stars in the sky are systems of two or more stars.   Those stars will be eclipsing binaries only if they are aligned along our line of sight.

10.  Which of the following statements about rotating variable stars is/are true?
a.  their brightness could vary because of darker regions along the photosphere
b.  their brightness could vary because of their ellipsoidal shape

A sufficiently large spot will diminish a star's brightness.  Also, the components within an ellipsoidal binary star appear to change in brightness as they rotate and revolve around each other because they we will alternately see their longer side and then narrower side during these rotations and revolutions.  

11. Which of the following is/are type(s) of intrinsic variables?
a.  pulsating
c. cataclysmic 
Intrinsic variable stars are those whose variability results from internal processes.   We divide these variables into two types:  pulsating and cataclysmic 

12.  How many different types of Cepheid variables have been identified?
b.  2
We recognize two types of Cepheids.    Type I and Type II

13.  What mechanism is believed to be responsible for Cepheid variability?
a.  doubly ionized helium
As the helium layer contracts due to the Cepheid's gravitational attraction, it absorbs heat and in the process becomes more ionized.  Doubly ionized helium is more opaque than singly ionized helium or neutral helium. As it is more opaque, it collects more heat.  (As an analogy, think of how darker colors absorb more heat than lighter ones.)    As the doubly ionized helium layer heats up, it begins to expand.  The expansion causes the layer to cool.  The cooled helium then regains an electron to become singly ionized.    The singly ionized helium, being less opaque,  allows more heat to escape.  The expansion ceases and the gravitational contraction resumes.  The compressed layer then heats, the helium becomes doubly ionized and the layer becomes more opaque.    The heating induces the next expansion and the cycle continues again.   

14. Why would a star's brightness change because of pulsations?
a. the change in size and temperature affects the luminosity, or energy output
A star's luminosity is proportional to the square of its radius and the fourth power of its temperature.  As the star pulsates, it contacts and expands, changing the size and temperature.

15.  The longer a Cepheid's variability period, the _____________ the Cepheid.
a. more luminous
The Period-Luminosity Relation states that the brighter the Cepheid variable the longer the variability period.  An astronomer can determine a Cepheid's absolute magnitude (intrinsic brightness) simply by observing this variability period. It is for this reason that Cepheids are so useful as distance indicators.   



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