The Solar System  Bulletin Board

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9/30/2008        Important!!! Exam Info!!!  I have discovered that the scanning machine that scored your Exam 01

has did not pick up many of your entries.  This might explain why the scores are so low.

Check your exam result sheet! If some of your incorrect answers occurred because of blanks

(the entry will say blank), the machine probably did not pick up your circled answer and it might

actually be correct!  If you have blanks listed on your exam results sheet and you know that

you circled an entry, bring your score sheet to me so that I can correct this problem

and record your correct score!

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9/19/2008        Please note …

1.       HW_02 due Tues 23 Sep

2.      Exam01 on Thurs 25 Sep!

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9/1/2008          1.  I modified HW assignments 2-6 in order to make some of the math questions

                        a little bit easier.  Please make sure that the files you access these assignments AFTER

                        9/1/2008!

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08/22/08          1. The syllabus for Fall Semester 2008 is available. Pay attention to Exam and HW Due dates!

                        It is your responsibility to be in class on those dates!

 

                        2. Google Earth has a new feature that you can use to observe the night sky …constellations, planets, motions,

                        etc.  It also has a lot of information about astronomical objects and processes that you might find interesting

                        and helpful.  T o download … go to www.earth.google.com and follow the “bouncing ball.”

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HW hints        Hint for question 15, hw01…The winter solstice occurs when the Sun is “in the constellation, Capricorn.”

                        (At least, it was Capricorn, before precession shifted the direction towards the constellation, Sagittarius!)

That’s why latitude -23.5 o is called the Tropic of Capricorn.  So, draw a picture …

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Complete the picture and figure out the relevant angles …

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                        Hint for Problem 17 HW_01 …

                        In order to figure out the phase of the Moon at any particular time, you need to know its position on the celestial

                        Sphere relative to the position of the Sun. The problem states that it is the 1st day of spring in the northern

                        hemisphere… so where must the Sun be?  It must lie in the direction of the vernal equinox … the direction

                        along a line of the intersection of the plane of the ecliptic and the celestial equator. (3 months later, the Sun will lie

                        inthe direction of the summer solstice.)

                        Now, the problem asks first … what is the phase of the Moon on the 1stday of spring … IF the Moon lies in

                        the direction of the vernal equinox … which would be the same direction as the Sun… right????  The question

                        is repeated for three addition possible directions of the Moon also on the 1stday of spring.

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Hint for question 13, HW_02…Take a look at Box5-2!  The luminosity,or intrinsic brightness, of a star depends upon its size and its surface temperature.  The bigger it is ---the brighter it is and the hotter it is --- the brighter it is.  The rate at which light energy per unit surface area pours out of a star of any size is called the light flux F and it is given by the following formula…

 

            where s is a constant and T is the surface temperature of the star.

 

In other words, if the temperature of a star suddenly doubled, its rate of energy output through each square meter of its surface would increase 16-fold!  The luminosity L of a star or the total rate at which it pours out energy depends on its surface area as follows …

 

           

  where A is the surface area of the star and is equal to …the surface area of a sphere of radius R.

           

Now put this altogether and calculate the relative brightness of the two stars in the problem.

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                        Hint … how to do HW_04, problem 11

                        Click here:       hint_HW04.11

                        Hint … how to do HW_03, problem 20

                        Click here:       hint_HW03.20

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