<p>You are correct that a star rises 4 minutes earlier each night, and therefore is sets 4 minute earlier. Therefore, b is the correct answer.</p>
<p>The reason for the 4 minute difference from night to night is because (a) the Earth orbits the Sun, (b) the Sun is close, and (c) the stars are much farther away. This can be understood from the following figure:
<a href="https://i.sstatic.net/RRgUe.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/RRgUe.png" alt="sidereal vs solar" /></a></p>
<ol>
<li>From your position on Earth, imagine the Sun and star X are overhead (or more accurately, on the meridian - the line from due south to the point overhead to due north).</li>
<li>After 23 hours 56 minutes, the same star is overhead (on the meridian). Because of the Earth's motion around the Sun, the Sun has not yet returned to the same position.</li>
<li>After another 4 minutes (so a total of 24 hours), the Sun is again overhead.</li>
</ol>
<p>Therefore, the star is overhead (on the meridian) 4 minutes earlier each day. Likewise, the star rises and sets 4 minutes earlier each day.</p>
<p>Note that the figure is not to scale, and my description ignores the Equation of Time. (Our clocks operate at a uniform rate. Due to the eccentricity of the Earth's orbit and the obliquity of Earth's axis, the Sun takes a few seconds longer or shorter to return to the point where it is on the meridian.)</p>

CC BY-SA 4.0
2021-06-25T16:51:29.733Z
2021-06-25T16:51:29.733Z
JohnHoltz
<p>The siderean (star)time is a bit different from the solar time. Because the Earth moves around the sun. If the Earth didn't rotate around its own axis the sun would rotate around the Earth once a year(seen from Earth). The stars wouldn't rotate at all. So the sun makes an extra round once a year. Take it from there.</p>

CC BY-SA 4.0
2021-06-25T13:27:45.537Z
2021-06-25T13:27:45.537Z
Deschele Schilder
<p>In the book <em>Thinking Physics</em> by Lewis Caroll I came accross the following exercise:</p>
<blockquote>
<p>Using a good digital watch, get the exact time when a bright star goes behind a distant building or tower. A day later time the disappearance again. Sighting over a nail fixed in a window sash will help you return your eye to the same location for each sighting. It will be found that</p>
<ol>
<li>the star disappears at the same time each night</li>
<li>the star disappears a little earlier each night</li>
<li>the star disappears a little later each night</li>
</ol>
</blockquote>
<p>I am thinking that each Night stars come up 4 min earlier so the answer must be b. Could you help me with the reasoning, please?</p>

CC BY-SA 4.0
2021-06-25T08:21:23.093Z
Welcome to astronomy SE! I’m voting to close this question for similar reasons, but I am happy to retract my vote if you edit your question, in particular if (a) you textify your screenshot as quote and (b) add a bit more details why you struggle with this question, and (c) you include the source of your quote.
B--rian
CC BY-SA 4.0
2021-06-25T12:20:52.957Z
Welcome to astronomy SE. I did suggest some edit which might make increase the probability of your question to being answered.
B--rian
CC BY-SA 4.0
2021-06-25T13:30:08.813Z
This is obviously no homework question. There are no popular books of science used in school.
Deschele Schilder
CC BY-SA 4.0
2021-06-25T14:32:12.563Z
While the asker has clarified in this case that it is not a homework question, I should remind everyone that homework questions *are* allowed here: https://astronomy.meta.stackexchange.com/questions/87/homework-policy/88#88

You're certainly not required to answer them, and you can downvote them if you want, but they cannot be closed as off topic.
called2voyage
<star><observational-astronomy>
Setting of stars
Particle king
# Setting of stars

(Asked by: username_0 on 2021-06-25)

In the book *Thinking Physics* by Lewis Caroll I came accross the following exercise:

> Using a good digital watch, get the exact time when a bright star goes behind a distant building or tower. A day later time the disappearance again. Sighting over a nail fixed in a window sash will help you return your eye to the same location for each sighting. It will be found that
>
> 1. the star disappears at the same time each night
> 2. the star disappears a little earlier each night
> 3. the star disappears a little later each night

I am thinking that each Night stars come up 4 min earlier so the answer must be b. Could you help me with the reasoning, please?

**Tags:** star, observational-astronomy
> **Comments:**
> **username_1**: Welcome to astronomy SE! I’m voting to close this question for similar reasons, but I am happy to retract my vote if you edit your question, in particular if (a) you textify your screenshot as quote and (b) add a bit more details why you struggle with this question, and (c) you include the source of your quote.  
> **username_1**: Welcome to astronomy SE. I did suggest some edit which might make increase the probability of your question to being answered.  
> **username_2**: This is obviously no homework question. There are no popular books of science used in school.  
> **username_3**: While the asker has clarified in this case that it is not a homework question, I should remind everyone that homework questions *are* allowed here: https://astronomy.meta.stackexchange.com/questions/87/homework-policy/88#88  You're certainly not required to answer them, and you can downvote them if you want, but they cannot be closed as off topic.  

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## 2 answers

### Answer by username_4 on 2021-06-25. Score: 4 | Accepted answer

You are correct that a star rises 4 minutes earlier each night, and therefore is sets 4 minute earlier. Therefore, b is the correct answer.

The reason for the 4 minute difference from night to night is because (a) the Earth orbits the Sun, (b) the Sun is close, and (c) the stars are much farther away. This can be understood from the following figure:
[![sidereal vs solar](https://i.sstatic.net/RRgUe.png)](https://i.sstatic.net/RRgUe.png)

1. From your position on Earth, imagine the Sun and star X are overhead (or more accurately, on the meridian - the line from due south to the point overhead to due north).
2. After 23 hours 56 minutes, the same star is overhead (on the meridian). Because of the Earth's motion around the Sun, the Sun has not yet returned to the same position.
3. After another 4 minutes (so a total of 24 hours), the Sun is again overhead.

Therefore, the star is overhead (on the meridian) 4 minutes earlier each day. Likewise, the star rises and sets 4 minutes earlier each day.

Note that the figure is not to scale, and my description ignores the Equation of Time. (Our clocks operate at a uniform rate. Due to the eccentricity of the Earth's orbit and the obliquity of Earth's axis, the Sun takes a few seconds longer or shorter to return to the point where it is on the meridian.)


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### Answer by username_2 on 2021-06-25. Score: 2

The siderean (star)time is a bit different from the solar time. Because the Earth moves around the sun. If the Earth didn't rotate around its own axis the sun would rotate around the Earth once a year(seen from Earth). The stars wouldn't rotate at all. So the sun makes an extra round once a year. Take it from there.


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