A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Frank Reed
Date: 2022 Jun 15, 11:10 -0700
Dave Walden, you wrote:
"It's 13 June 2022, 2h 20m 8.1s UT. You see delta Scorpii (Dschubba) disappear behind the moon.
At 3h 5m 30s, you see it reappear. Where are you?"
Here's a relatively "lazy" approach to this puzzle: visit the IOTA page for this occultation here: http://www.lunar-occultations.com/iota/bstar/0613zc2290.htm. Then use a plain text search in your web browser to find times that are close. Be aware that the listed locations probably derive from an ancient database since they refer to an idiosyncratic selection of airports, not city or town centers. For example, the timings for New York, NY are for LaGuardia in Queens, and the timings for Providence, RI are for "Rhode Island T.F. Green International Airport" (its new long name) which is in Warwick, RI. They also list Muir, PA, which is an insignificant small town, but the location refers to Muir Army Airfield. Like I say, it's an idiosyncratic selection.
Another approach: simulate the occultation in Stellarium and do a two-dimensional binary search (in other words, try a lat/lon pair and see if it's better or worse than the last pair). I used this method first and found a location in northern New Jersey that fits well.
I notice in Stellarium that this star is a double. Should we worry about that? And should we worry about observer altitude above sea level? The Moon's parallax is larger at altitude, and this can be simulated directly in Stellarium. Fortunately, New Jersey's "mountains" are not very high, though they do include part of the famous Appalachian Trail.
Stellarium is reasonably accurate for occultations like this in terms of pure astrometry, but it ignores the lunar limb, which can change the timings by some seconds. I'm not entirely sure about the IOTA tables, linked above, but I believe they do include the lunar limb profile in their predictions. Assuming that's the case and doing some visual interpolation, I would move the "fix" to the vicinty of Somerset, NJ, about 25km SSE of the result from Stellarium. But that's just a rough estimate founded on an assumption. Would anyone care to do it properly based on the actual lunar limb?
Clockwork Mapping / ReedNavigation.com
Conanicut Island USA