We know that the flux received by a star of fixed intrinsic brightness falls off as the inverse square of the distance to that star. This is shown in the following table:

Distance

flux received
by detector

10 Light years

1600 units

20 Light years

400 units

40 Light years

100 units

80 Light years

25 units


  1. If the star in the above table had a distance of 5 light years, the flux received by the detector would be:

    1. 1600 units
    2. 2400 units
    3. 3200 units
    4. 4800 units
    5. 6400 units

    Now consider this scenario

    Star

    Distance

    flux received
    by detector

    Relative Brightness
    to Star A

    A

    10 Light years

    1600 units

    1

    B

    20 Light years

    1600 units

    4

    C

    40 Light years

    1600 units

    16

    D

    80 Light years

    1600 units

    64

  2. Star E has a distance of 40 light years and a measured flux of 3200 units. Relative to Star A, the brightness of star E is

    1. the same
    2. 2 times greater
    3. 16 times greater
    4. 32 times greater
    5. 64 times greater

    You observe 4 stars in the sky. Their properties are summarized in the table below:

    Star Flux on Detector
    (Arbitrary Units)     		Distance
    (Light Years)     		Observed
    Color
    A 2 2 Blue
    B 4 4 Red
    C 5 4 Very Blue/White
    D 16 1 Yellow

  3. Which of these stars has the coolest surface temperature:

    1. A
    2. B
    3. C
    4. D

  4. Which of these stars has the highest luminosity (i.e. which is producing the most energy)?

    1. A
    2. B
    3. C
    4. D

  5. Which of these stars has the lowest luminosity?

    1. A
    2. B
    3. C
    4. D

  6. What is is the ratio of luminosities between Star D and Star A

    1. they are the same
    2. 2 to 1
    3. 4 to 1
    4. 8 to 1



    Download the blackbody simulator for this part

  7. What temperature produces a peak emission around 4000 angstroms?

    1. 6000 K
    2. 6400 K
    3. 7000 K
    4. 7400 K
    5. 7800 K

  8. Approximately what temperature produces a B-V index value of 1.0

    1. 7500 K
    2. 6000 K
    3. 4300 K
    4. 3800 K
    5. can't tell from the information given

  9. Click on Star Data and Select the star G1--2V. What is the approximate black body temperature of this star?

    1. 3000 K
    2. 4000 K
    3. 5000 K
    4. 5500 K
    5. 6400 K

  10. Now select the star labeled B6V. What is the approximate black body temperature of this star?

    1. 13000 K
    2. 15000 K
    3. 17000 K
    4. 19000 K
    5. 22000 K