# NASA Eclipse Calculations Accuracy

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## Main Question or Discussion Point

How accurate do you think NASA's eclipse calculations are?

Will that aircraft provide accurate moon trajectory?

## Answers and Replies

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mfb
Mentor
We know the relative position of Earth and Sun with an accuracy of meters from radar astronomy, and the position of Moon relative to Earth with a precision of centimeters from Lunar Laser Ranging.

The calculations are exact for all practical purposes.

davenn and Xilus
A.T.
How accurate do you think NASA's eclipse calculations are?
Here an app for navigation and some hints for watching it:

Xilus
I was watching on C-Span all night long.

NASA's numbers were right on. That's a difficult calculation. I want to hear more from NASA.

NASA's numbers were right on. That's a difficult calculation. I want to hear more from NASA.
NASA's eclipse maps were apparently based on far more data than just the relative positions of the three bodies. See these articles from NASA -

12/14/16 - Tracing the 2017 Solar Eclipse

1/5/17 - NASA Moon Data Provides More Accurate 2017 Eclipse Path

6/12/17 - Shadow of the Eclipse

They all cover essentially the same topic. Here are some excerpts - the first paragraph is from "Tracing the 2017 Solar Eclipse"; the remainder is from "NASA Moon Data Provides More Accurate 2017 Eclipse Path" - note that the LRO mentioned in the quote at the end is the Lunar Reconnaissance Orbiter:

When depicting an eclipse path, data visualizers have usually chosen to represent the moon's shadow as an oval. By bringing in a variety of NASA data sets, visualizer Ernie Wright has created a new and more accurate representation of the eclipse. For the first time, we are able to see that the moon's shadow is better represented as a polygon. This more complicated shape is based on NASA's Lunar Reconnaissance Orbiter's view of the mountains and valleys that form the moon's jagged edge. By combining moon's terrain, heights of land forms on Earth, and the angle of the sun, Wright is able to show the eclipse path with the greatest accuracy to date . . .

Wright . . . created a continuously varying lunar limb profile as the moon’s shadow passes over the United States as it will during the upcoming eclipse. The mountains and valleys along the edge of the moon’s disk affect the timing and duration of totality by several seconds. Wright also used several NASA data sets to provide an elevation map of Earth so that eclipse observer locations were depicted at their true altitude.

The resulting visualizations show something never seen before: the true, time-varying shape of the moon’s shadow, with the effects of both an accurate lunar limb and the Earth’s terrain.

"We couldn’t have done visualizations like this even 10 years ago,” Wright said. “This is a confluence of increasing computing power and new datasets from remote sensing platforms like LRO and the Shuttle Radar Topography Mission.”​

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We can predict eclipses thousands of years into the future and past.
Wikipedia ain't NASA, but they do have a section of their article on solar eclipses that deals with prediction & might be relevant to the OP's question:

https://en.wikipedia.org/wiki/Solar_eclipse#Predictions

And useful for explaining some of these concepts simply is the "About Solar Eclipses" page at Eclipse Chasers: https://www.eclipse-chasers.com/article/beginner/tseAbout.shtml

E.g. scroll down the "About Solar Eclipses" page to the section on "Saros Series". This comes up in the Wikipedia article, as well as in a couple of related articles, https://en.wikipedia.org/wiki/Eclipse_cycle and https://en.wikipedia.org/wiki/Saros_(astronomy)

And NASA gives some interesting history here: https://eclipse2017.nasa.gov/eclipse-history

mfb
Mentor
Wikipedia ain't NASA
The Wikipedia pages have their data from NASA. Currently NASA directs all views to the 2017 eclipse page, but you can still find the reference via web archives. Example

Andy Resnick
On a related note, I missed getting a shot of the ISS as it passed in front of the sun during the eclipse- presumably the NASA trackers knew what was going to happen, but my usual databases didn't mention it. Did anyone here know this was going to happen?

Currently NASA directs all views to the 2017 eclipse page, but you can still find the reference via web archives. Example
I hope they restore all the old links that Wikipedia is using - those are redirecting also. Somewhat overkill to do a total redirect of all relevant pages; unless it was to do with preparing for massive server traffic?

mfb
Mentor
On a related note, I missed getting a shot of the ISS as it passed in front of the sun during the eclipse- presumably the NASA trackers knew what was going to happen, but my usual databases didn't mention it. Did anyone here know this was going to happen?
As long as the eclipse is not too far north/south (~55°N/S) and lasts longer than one ISS orbit (~90 minutes), there is always at least one point where the ISS transits the Sun during the eclipse. There were one or two narrow corridors (~3 km wide) in the US where such a double transit was visible.