Astronoimical Gift for an Interested Non-Astronomer

[old_eyes]

My son recently got married in the US, and when asked what he wanted as a wedding present he mentioned that he and his wife had seen an "astronomical map" at the Hoover Dam that recorded the exact moment that the dam was inaugurated, and would be readable for thousands of years, even by alien archaeologists. Could he have something like that to remember his wedding.

An interesting challenge!

I could not find that much detail about the Hoover Dam map and how it works. It appears quite complicated and to involve many parts. There is information here and here.

The map is the work of Oskar Hansen, and he wrote of it:

"Surrounding the base is a terrazzo floor, inlaid with a star chart, or celestial map. The chart preserves for future generations the date on which President Franklin D. Roosevelt dedicated Hoover Dam, September 30, 1935.

The apparent magnitudes of stars on the chart are shown as they would appear to the naked eye at a distance of about 190 trillion miles from earth. In reality, the distance to most of the stars is more than 950 trillion miles.

In this celestial map, the bodies of the solar system are placed so exactly that those versed in astronomy could calculate the precession (progressively earlier occurrence) of the Pole Star for approximately the next 14,000 years. Conversely, future generations could look upon this monument and determine, if no other means were available, the exact date on which Hoover Dam was dedicated."

I couldn't copy Hansen's approach as there was not enough information beyond the fact that it used the precession of the celestial North Pole with its 26,000 year period as one key piece of information.

I played with a number of ideas, including using the positions of the planets as seen from above the plane of the Solar System as a clock and playing with the precession of the North Pole, but none of them connected with what they could see in the sky.

So I took a different approach. I set CdC to the exact date time and location of their wedding and got it to produce a Mercator projection of the whole sky and printed it as a raster image. I added in some labels for Solar System Objects and the moon with the correct phase, thickened some of the grid lines and generally tidied up a bit.

The image was chemically etched into a A4 sized piece of stainless steel (that should have a pretty long life) with an added inscription (which I don't expect the alien archaeologists to understand!)

Below is a poor photo of it as it was all done in a mad rush before a trip to see them, and the plaque arrived the day before we left! If I get a better picture from him I will edit the post.

It was a fun project, and the recipients are delighted with it.

How accurately will it pinpoint the moment is up for debate. The 88 day orbital period of Mercury and positions of the sun and moon against the sky give fine resolution and the outer planets give longer time information. However, apart from the accuracy of CdC and the precision of the etching process, the orbits of the outer planets are sufficiently in doubt to limit the clock accuracy. Plus over thousands of years orbital interactions and resonances may move things about.

But it should be usable until I snuff it, and after that it is someone else's problem!

 

[MarsG76]

What a great idea... nice one.

[JOC]

Neat, it reminds me of two pressies I got in the past for my parents that they have been pleased with.  One was an electronic weather station with a feed to a unit into their lounge and the more related one was a latitude correct sundial complete with the date of their wedding etched into it for their Ruby wedding and the equation of time for correction.  Neither as inventive as your suggestion, but both are nice ideas if anyone wants something 'different' for their older parents.  The Sundial is completely accurate too!