Anonymous
Anonymous asked in Science & MathematicsAstronomy & Space · 4 weeks ago

help with Astronomy?

Here’s a practice question: ​Suppose Sherlock Holmes is investigating a murder that took place at 3 AM in a dark alley. A witness claims he recognized the killer in the light cast by a first quarter moon. Should the detective believe him?

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  • 1. No. A first-quarter moon has set by 3 am.

  • 4 weeks ago

    The first quarter moon rises about noon, so it'll set about midnight.  At 3am, it's below the horizon. 

    Arrest that man. 

  • 4 weeks ago

    That depends on how precise you believe the witness has to be on recognizing the phase of the moon.  Or on what the actual phase was.

    For example: The phase of the moon tonight is just past First Quarter.  Moonrise today was about 2:00 PM here, and moonset will be about 11:30 PM.  But in less than a week it will set at about 3:30 AM.  The witness could have misidentified the phase as First Quarter when it was really a few days later.

    Or another possibility:  Less than two weeks ago, the phase of the moon was Third Quarter.  Moonrise was just after midnight, and moonset was 3:30 in the afternoon.  In that case the moon would have certainly been visible, but the witness might have mistaken Third Quarter for First Quarter.  The only visible difference is which side (left or right) of the moon is lit.

    Either way, the lit portion of the moon, if it was above the horizon, might certainly have provided enough light to see by.

  • 4 weeks ago

    No. A first quarter Moon SETS well before 3 am 

    September 24 is first quarter Moon. It will set before 3 am. 

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