<p>You'll need a starting point (an &quot;epoch time&quot;) to do this, and that will require a calendar day of week. The observed state of the solar system was used as the basis of the calendar for quite some time. That we have twelve months in a year is partly a result of old civilizations that used base 12 or base 60 rather than base 10. (The same applies to the concept of 24 hours per day.) Weeks comprising seven days are partly based on phases of the Moon, but that relationship is nowhere close to perfect.</p>
<p>You'll need an accurate ephemeris and an epoch date (including day of week) to be able to do this.</p>

CC BY-SA 4.0
2022-10-24T15:53:33.140Z
2022-10-24T15:53:33.140Z
David Hammen
<p>Can any day of the week be identified by only observing the stellar bodies without calendars nor satellite?</p>

CC BY-SA 4.0
2022-10-24T15:08:45.800Z
What do you mean "without calender"? Do I have a clock? Day-of-week is a definition bound to a calender. Astronomically only year and day are well-defined by the orbital and spin period of Earth. One may argue about the lunar month, but beyond that, the rest is human definition which essentially is some form of calender to sub-divide the year into managable units of time.
planetmaker
CC BY-SA 4.0
2022-10-24T15:48:08.810Z
Please clarify your specific problem or provide additional details to highlight exactly what you need. As it's currently written, it's hard to tell exactly what you're asking.
Community
CC BY-SA 4.0
2022-10-24T18:43:29.643Z
You really need to better specify what information you want to base the calculation on.  E.g. a suitable answer to your question as is would be "On Monday at sunset, the next time the Sun rises it will be Tuesday" [outside of the arctic circle].  But I don't think you'd find such an answer too helfpul.
Greg Miller
CC BY-SA 4.0
2022-10-24T20:46:29.380Z
Heck, you'll need to know your time zone and position on Earth as well, as there can be as many as three different days of the week simultaneously at different places on Earth.
notovny
CC BY-SA 4.0
2022-10-25T00:23:16.360Z
Welcome to *Astronomy Stack Exchange!* This is an interesting first question by a new user and I don't think it deserves all the down voting and close voting. Don't worry about it. You can respond to some of the comments like "Do I have a clock" by editing your question and adding the information there. Basically the week is such an artificial construct that (as far as I can tell) there's absolutely no connection to what's happening with Earth's or the Moon's orbit or anything else. We can get nigh and day, and time of year, but everything else comes from calendars and clocks and diligence.
uhoh
CC BY-SA 4.0
2022-10-25T00:37:52.653Z
Considering that this question quite clear and is already nicely answered by @DavidHammen I disagree with the proposed close votes for "include more details and clarify the problem." It's completely clear, we don't vote to close just because the OP didn't respond to our query in comments. That's not a close reason. "You didn't answer me, so now nobody should be able to post an answer. *There!*" Therefore **voting to leave open**.
uhoh
CC BY-SA 4.0
2022-11-02T00:00:02.997Z
You can determine the date of any observation from the positions of the objects observed. You have to pick and choose to find the right objects to use. Converting date to day of the week is trivially simple, even without a calendar. If you answer the questions in the earlier comments, you'll get a complete answer from someone.
stretch
<observational-astronomy>
Can astronomy determine the days of the week
Charlo
# Can astronomy determine the days of the week

(Asked by: username_0 on 2022-10-24)

Can any day of the week be identified by only observing the stellar bodies without calendars nor satellite?

**Tags:** observational-astronomy
> **Comments:**
> **username_1**: What do you mean "without calender"? Do I have a clock? Day-of-week is a definition bound to a calender. Astronomically only year and day are well-defined by the orbital and spin period of Earth. One may argue about the lunar month, but beyond that, the rest is human definition which essentially is some form of calender to sub-divide the year into managable units of time.  
> **username_2**: Please clarify your specific problem or provide additional details to highlight exactly what you need. As it's currently written, it's hard to tell exactly what you're asking.  
> **username_3**: You really need to better specify what information you want to base the calculation on.  E.g. a suitable answer to your question as is would be "On Monday at sunset, the next time the Sun rises it will be Tuesday" [outside of the arctic circle].  But I don't think you'd find such an answer too helfpul.  
> **username_4**: Heck, you'll need to know your time zone and position on Earth as well, as there can be as many as three different days of the week simultaneously at different places on Earth.  
> **username_5**: Welcome to *Astronomy Stack Exchange!* This is an interesting first question by a new user and I don't think it deserves all the down voting and close voting. Don't worry about it. You can respond to some of the comments like "Do I have a clock" by editing your question and adding the information there. Basically the week is such an artificial construct that (as far as I can tell) there's absolutely no connection to what's happening with Earth's or the Moon's orbit or anything else. We can get nigh and day, and time of year, but everything else comes from calendars and clocks and diligence.  
> **username_5**: Considering that this question quite clear and is already nicely answered by @DavidHammen I disagree with the proposed close votes for "include more details and clarify the problem." It's completely clear, we don't vote to close just because the OP didn't respond to our query in comments. That's not a close reason. "You didn't answer me, so now nobody should be able to post an answer. *There!*" Therefore **voting to leave open**.  
> **username_6**: You can determine the date of any observation from the positions of the objects observed. You have to pick and choose to find the right objects to use. Converting date to day of the week is trivially simple, even without a calendar. If you answer the questions in the earlier comments, you'll get a complete answer from someone.  

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## 1 answers

### Answer by username_7 on 2022-10-24. Score: 2

You'll need a starting point (an "epoch time") to do this, and that will require a calendar day of week. The observed state of the solar system was used as the basis of the calendar for quite some time. That we have twelve months in a year is partly a result of old civilizations that used base 12 or base 60 rather than base 10. (The same applies to the concept of 24 hours per day.) Weeks comprising seven days are partly based on phases of the Moon, but that relationship is nowhere close to perfect.

You'll need an accurate ephemeris and an epoch date (including day of week) to be able to do this.


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