<p>To answer the question directly.  No, we can't be certain this observation is not correct.</p>
<p>Astronomy can say where the moon is, and how much of the moon is illuminated.  We know that at the time, the moon would have been close to the sun in the evening sky, which is where the claimed observation occurred.  We know it would only have been visible for a short time, as it set soon after.</p>
<p>What astronomy can't say is how the atmosphere will affect visibility, and how different people's eyes will respond to the very slight difference in sky brightness around the crescent. It can't account for the psychological effect of wish fulfilment - nor can it account for deliberate fraud and deception.</p>
<p>And cameras or telescopes can't help. There is a lot that is visible with a camera attached to a telescope that is not visible to the naked eye.  There is a question here with a telescope image of not only Jupiter but also its moons during the day. If Calisto can be seen during the day with a telescope, perhaps the crescent can too. Does that &quot;count&quot;?  Only a expert in Islamic law and traditions can decide (an in practice different experts have different opinions)</p>
<p>The calculations of visibility are based on a simple model. The astronomy is fairly easy. Eyes and brains are not.</p>

CC BY-SA 4.0
2023-04-27T19:58:07.953Z
2023-04-27T19:58:07.953Z
James K
<p>The moon has reportedly been observed on the evening of 20/04/2023 in Tumair, Saudi Arabia, marking the end of Ramadan. According to some websites such as <a href="https://www.moonsighting.com/1444shw.html" rel="nofollow noreferrer">this one</a>, this cannot happen. I was wondering how accurate these calculations are, and can we say <strong>for sure</strong> the moon has not been observed?</p>

CC BY-SA 4.0
2023-04-25T21:22:28.383Z
I see there is some news about this sighting (https://twitter.com/theholymosques/status/1648997000707297280) in some of the photos there are telescopes of various sizes. Websites that predict visibility will use some very simple approximate model for twilight and *practical* visibility for casual observers, and these folks are definitely *serious observers* with serious equipment! I can't write a proper Stack Exchange answer, but I'd say unless a website publishes their algorithm and all assumptions used, one can't really address its accuracy. And use of telescopes changes everything.
uhoh
CC BY-SA 4.0
2023-04-25T22:26:41.610Z
Predicting the position of the Sun and Moon to sub-arcsecond accuracy, is not a difficult task.  Especially with all of the modern astronomy libraries available.  Predicting the *visibility* is going to be where the large error margin comes in.  With the emphasis so many people put on this event, there has been a lot of good research put into it, but it's tough to do a controlled study on such a thing.
Greg Miller
CC BY-SA 4.0
2023-04-26T09:43:29.740Z
@uhoh they may well have the latest telescopes, but what puzzles me is that they don't share a photo/video of the observed moon. Don't these sophisticated telescopes have a recording option?! And yes, very valid point regarding the algorithms/assumptions which need to be published.
Ali Hassaine
CC BY-SA 4.0
2023-04-26T17:32:55.890Z
It may well be possible to get a photo of the moon long before it is visible - in the generally understood way. Whether the moon is visible depends greatly on meteorological (clarity of the air), physiological (acuity of the eyes) and technological (if telescopes, and cameras are considered okay) rather than astronomical (the relative position of the moon and sun).
James K
CC BY-SA 4.0
2023-04-26T17:34:15.240Z
Add to this the psychological - the kudos that comes with being "first" to spot the moon. And you have a perfect mix for people to honestly claim a sighting that never actually happened.
James K
CC BY-SA 4.0
2023-04-29T13:42:47.830Z
From what I heard, orthodox Muslims will require a *visual* observation of the Moon—i.e., with the naked eyes, as opposed to a telescopic one—to determine the start of a new month.

Photographing the Moon is possible in practically all circumstances; French astrophotographer Thierry Legault has managed to capture an image at the instant of new moon—it was at some distance north or south of the Sun, enough for a very thin sliver to be visible. So, it all depends what definition of “observe the Moon” you follow: By eye, or by telescope?
Pierre Paquette
<the-moon>
Moonsighting on 20/04/2023 in Tumair KSA
Ali Hassaine
# Moonsighting on 20/04/2023 in Tumair KSA

(Asked by: username_0 on 2023-04-25)

The moon has reportedly been observed on the evening of 20/04/2023 in Tumair, Saudi Arabia, marking the end of Ramadan. According to some websites such as [this one](https://www.moonsighting.com/1444shw.html), this cannot happen. I was wondering how accurate these calculations are, and can we say **for sure** the moon has not been observed?

**Tags:** the-moon
> **Comments:**
> **username_1**: I see there is some news about this sighting (https://twitter.com/theholymosques/status/1648997000707297280) in some of the photos there are telescopes of various sizes. Websites that predict visibility will use some very simple approximate model for twilight and *practical* visibility for casual observers, and these folks are definitely *serious observers* with serious equipment! I can't write a proper Stack Exchange answer, but I'd say unless a website publishes their algorithm and all assumptions used, one can't really address its accuracy. And use of telescopes changes everything.  
> **username_2**: Predicting the position of the Sun and Moon to sub-arcsecond accuracy, is not a difficult task.  Especially with all of the modern astronomy libraries available.  Predicting the *visibility* is going to be where the large error margin comes in.  With the emphasis so many people put on this event, there has been a lot of good research put into it, but it's tough to do a controlled study on such a thing.  
> **username_0**: @uhoh they may well have the latest telescopes, but what puzzles me is that they don't share a photo/video of the observed moon. Don't these sophisticated telescopes have a recording option?! And yes, very valid point regarding the algorithms/assumptions which need to be published.  
> **username_3**: It may well be possible to get a photo of the moon long before it is visible - in the generally understood way. Whether the moon is visible depends greatly on meteorological (clarity of the air), physiological (acuity of the eyes) and technological (if telescopes, and cameras are considered okay) rather than astronomical (the relative position of the moon and sun).  
> **username_3**: Add to this the psychological - the kudos that comes with being "first" to spot the moon. And you have a perfect mix for people to honestly claim a sighting that never actually happened.  
> **username_4**: From what I heard, orthodox Muslims will require a *visual* observation of the Moon—i.e., with the naked eyes, as opposed to a telescopic one—to determine the start of a new month.  Photographing the Moon is possible in practically all circumstances; French astrophotographer Thierry Legault has managed to capture an image at the instant of new moon—it was at some distance north or south of the Sun, enough for a very thin sliver to be visible. So, it all depends what definition of “observe the Moon” you follow: By eye, or by telescope?  

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## 1 answers

### Answer by username_3 on 2023-04-27. Score: 3

To answer the question directly. No, we can't be certain this observation is not correct.

Astronomy can say where the moon is, and how much of the moon is illuminated. We know that at the time, the moon would have been close to the sun in the evening sky, which is where the claimed observation occurred. We know it would only have been visible for a short time, as it set soon after.

What astronomy can't say is how the atmosphere will affect visibility, and how different people's eyes will respond to the very slight difference in sky brightness around the crescent. It can't account for the psychological effect of wish fulfilment - nor can it account for deliberate fraud and deception.

And cameras or telescopes can't help. There is a lot that is visible with a camera attached to a telescope that is not visible to the naked eye. There is a question here with a telescope image of not only Jupiter but also its moons during the day. If Calisto can be seen during the day with a telescope, perhaps the crescent can too. Does that "count"? Only a expert in Islamic law and traditions can decide (an in practice different experts have different opinions)

The calculations of visibility are based on a simple model. The astronomy is fairly easy. Eyes and brains are not.


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