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[parent] mean solar time example problem (Example)

Mean Solar Time Problem

Problem Statement:

A sundial located in New York City (longitude $73.97^\circ$ W) shows a local apparent solar time of 12:00 PM when the sun is at its highest point in the sky. However, the standard time in New York (Eastern Time Zone, UTC-5) is different due to the equation of time and longitude correction.
  1. Calculate the mean solar time corresponding to this observation.
  2. Determine the difference between local apparent solar time and mean solar time if the equation of time on that day is $-6$ minutes.
  3. What is the standard clock time (Eastern Time) for this event, considering the longitude-based time zone adjustment?

Given:

  • Longitude of New York City: $\lambda = 73.97^\circ$ W.
  • Reference longitude for Eastern Time Zone: $\lambda_{\text{ref}} = 75^\circ$ W.
  • Equation of Time on the given day: $EoT = -6$ minutes.

Solution:

1. Mean Solar Time (MST) is related to Local Apparent Solar Time (LAST) by the equation:

   MST$\displaystyle =$   LAST$\displaystyle - EoT $
Since LAST is 12:00 PM,

   MST$\displaystyle = 12:00\,$PM$\displaystyle - (-6\,$min$\displaystyle ) = 12:06\,$PM$\displaystyle . $

2. Longitude Correction: The time zone is based on $\lambda_{\text{ref}} = 75^\circ$ W, but New York City is at $\lambda = 73.97^\circ$ W. The difference is:

$\displaystyle \Delta\lambda = 73.97^\circ - 75^\circ = -1.03^\circ. $
Since $15^\circ = 1$ hour, the time difference is:

$\displaystyle \Delta t = \frac{-1.03^\circ}{15^\circ/\text{hour}} = -0.0687\,\text{hours} \approx -4.12\,\text{minutes}. $

3. Standard Clock Time: The mean solar time must be adjusted by $\Delta t$ to get the standard time:

   Standard Time$\displaystyle =$   MST$\displaystyle + \Delta t = 12:06\,$PM$\displaystyle - 4.12\,$min$\displaystyle \approx 12:01.88\,$PM$\displaystyle . $

Final Answer:

The mean solar time is $12:06\,\,$PM, and the standard clock time is approximately $12:02\,\,$PM.

This is an example problem generated from DeepSeek AI using prompt, "For a physics class can you give an example problem for mean solar time and write it in latex".



"mean solar time example problem" is owned by bloftin.
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See Also: timescales based on Earth's rotation


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Cross-references: mean solar time

This is version 4 of mean solar time example problem, born on 2025-03-30, modified 2025-03-30.
Object id is 995, canonical name is MeanSolarTimeExampleProblem.
Accessed 43 times total.

Classification:
Physics Classification: 95.10.Km (Ephemerides, almanacs, and calendars)
 45.50.Pk (Celestial mechanics )
 95.10.-a (Fundamental astronomy)
Pending Errata and Addenda
None.
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