Question

If we observe a star over 6 months and obtain a parallax angle (p) for the star, how can we calculate the distance to the star?

Answer 1

Write the angle in seconds (1/3600 of a degree). It'll be less than 1 second for any star. Now, take the reciprocal of the number of seconds. (1/seconds). That number is the distance to the star, in "parsecs". 1 parsec = about 3.26 light years. The nearest star, Alpha Centauri, has a parallax of 0.75481 second. The reciprocal of that number is 1.3248 . Multiply that by 3.26156 light years per parsec, and you get 4.32103 light years. The awesome thing about it is how in the world they were able to measure 0.75481 of a second of parallax. That's 0.00020967 of one degree ! And they have to measure it between two times that are six months apart ! ! And that's the nearest star, with the greatest parallax ! ! ! Totally incredible.

Answer 2

Question 1  

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3 out of 3 points

   

 

A light-year is best defined as ________.

 

Selected Answer:  

Correct  

the distance that light travels in one year

   

Correct Answer:  

Correct  

the distance that light travels in one year

   

Response Feedback:  

A light-year is the distance light will travel in one year.

 

 

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Question 2  

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3 out of 3 points

   

 

If you say that something is 3,000 light-years away, you are stating that ________.

 

Selected Answer:  

Correct  

the light that we see from the object traveled for 3,000 years before reaching our eyes

   

Correct Answer:  

Correct  

the light that we see from the object traveled for 3,000 years before reaching our eyes

   

Response Feedback:  

This means that we are seeing light that left the object 3,000 years ago.

 

 

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Question 3  

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2 out of 2 points

   

 

The phenomenon of cosmological redshift demonstrates that the universe is expanding.

 

Selected Answer:  

Correct  

TRUE

   

Correct Answer:  

Correct  

TRUE

   

Response Feedback:  

This statement is true.

 

 

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Question 4  

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2 out of 2 points

   

 

Galaxies moving away from us will emit light that is redder than we would otherwise expect.

 

Selected Answer:  

Correct  

TRUE

   

Correct Answer:  

Correct  

TRUE

   

Response Feedback:  

This statement is true.

 

 

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Question 5  

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3 out of 3 points

   

 

A star has a high apparent magnitude and a low absolute magnitude. This star is likely

 

Selected Answer:  

Correct  

close to Earth

   

Correct Answer:  

Correct  

close to Earth

   

Response Feedback:  

This star is close to Earth, making it appear very bright to us.

 

 

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Question 6  

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3 out of 3 points

   

 

The magnitude of a star is an expression of a star’s

 

Selected Answer:  

Correct  

brightness

   

Correct Answer:  

Correct  

brightness

   

Response Feedback:  

Magnitude is an expression of brightness.

 

 

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Question 7  

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3 out of 3 points

   

 

Which of the following describes the brightness of a star as we see it from Earth?

 

Selected Answer:  

Correct  

apparent magnitude

   

Correct Answer:  

Correct  

apparent magnitude

   

Response Feedback:  

This is the apparent magnitude.

 

 

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Question 8  

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0 out of 3 points

   

 

Stars may shine brighter or dimmer depending on their age. What else may affect how brightly we see a star’s light?

 

Selected Answer:  

Incorrect  

location of the moon in relation to the star

   

Correct Answer:  

Correct  

distance from the star

   

Response Feedback:  

The distance from a star also affects brightness.

 

 

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Question 9  

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3 out of 3 points

   

 

If we observe a star over 6 months and obtain a parallax angle (p) for the star, how can we calculate the distance to the star?

 

Selected Answer:  

Correct  

distance = 1/p

   

Correct Answer:  

Correct  

distance = 1/p

   

Response Feedback:  

Distance is 1/p.

 

 

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Question 10  

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3 out of 3 points

   

 

A star’s parallax angle is 0.8. How far away is the star in parsecs?

 

Selected Answer:  

Correct  

1.25

   

Correct Answer:  

Correct  

1.25

   

Response Feedback:  

Distance is 1/p.