WAITING FOR THE SHADOW

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Observing the eclipse from the beach
Joe Cali

Any place with a good view of the east horizon will make a great place to watch the November 14th, 2012 Cairns Port Douglas total solar eclipse. Though the beach immediately comes to mind, the tide will be coming in as the eclipse progresses. Some beaches may become covered by tides . New Moon and totality occurs at 06:38. A high tide of about 3m occurs mid-morning (9:06am) on the day of the eclipse in this region. Tide height during totality will probably be about 2.3m. So the tide will be low at 2:30am and still low about the time you select your observing location pre-dawn. The tide will be coming in during the eclipse and high tide will occur about an hour after the total eclipse ends.  Oak beach might seem to be the perfect spot located on the beach and the centre line but the following photographs show why Oak Beach should be avoided. 


 




The tide pole base is 2m.    As best I could determine, treeline is about 3.1m AMSL. 





 
Four Mile Beach, Port Douglas


Four Mile beach is a very flat beach.  High tide regularly reaches the debris line level with the piece of driftwod in this photo and by 9am on eclipse day may well be lapping at the trees.

The marathon starts from the south end of the beach and then contestants run up the beach at the end of the race not at the beginning. At around 4th contact, the half marathon entrants will be running up the beach. One and a bit hours after this the first of the full marathon runners will be coming up the beach.

The half marathon runners might be running up the beach around 4th contact but they'll be spread out and effectively running single file.  Most eclipse chasers will be packing up or gone by then. People doing long time lapse sequences might find that runners on the beach makes for an interesting and different foreground to the cliche palm trees. At the beginning, they will be milling around at the start area at the south end of the beach. I don't know if they'll walk or jog down the beach to get there.
 
The marathon organizers seem to have attempted to minimize road closures and disruptions as much as possible. The marathon only crosses the Captain Cook highway once at the start and again once at the finish.  Most of the marathon is run on farm and bush tracks not on public roads to minimize disruption. The half marathon runners might be crossing that road and running up the beach at 4th contact but not much before.  Most likely, they'll have marshalls at the road crossings who will briefly close the roads, only while competitors cross, then reopen them.
 
The Captain Cook Highway is the only transport route along the coast. I have read where some have suggested they might close it for a day. This is a nonsense suggestion. Common sense dictates that even an hour closure would cause a major disruption. They won't close it,  if for no other reason than the inconvenience it would cause and the economic cost to the locals who cast their votes for the council. Local tour companies will still be running tours to Daintree, Mossman Gorge, Port Douglas supermarkets, shops, restaurants and hotels still need fresh food deliveries and reef cruises will still be sailing out of Port Douglas every day of the week.  That road is essential to their business.  Life doesn't stop because of a marathon or an eclipse.

One post on the solar eclipse mailing list asked (with resepect to the marathon) :
"And it remains to be seen whether viewing would even be able to be allowed from four mile beach, as the entire stretch is on the route."
 
In my opinion, you wouldn't necessarily want to watch the eclipse from Four Mile Beach. Because of the rising tides, you'll have to locate yourself at the treeline resulting in a poor view of the approaching shadow. The high tide will creep up quicker than convenient during the eclipse.  I had a poke around some online tidal models.  They seemed to spit out a tide height estimate at totality of about 2.3m.  This will cover most of Four Mile Beach and Oak beach at totality.  The incoming tide will, by 4th contact, cover most of the sand area of the beach leaving only a narrow strip for pedestrians. 
 
Here is an extract of the data. EST is Australian EST not USA.  The full raw uncorrected data set from midnight-10am on eclipse day is pasted at the bottom of this file.

Time EST
3:01
4:01
5:01
5:31
5:41
5:51
6:01
6:11
6:21
6:31
6:41
6:51
7:01
7:11
7:21
7:31
7:41
7:51
8:01		 TIDE (metres)
0.14
0.58
1.21
1.55
1.66
1.77
1.88
1.99
2.09
2.19
2.29
2.38
2.47
2.55
2.63
2.7
2.77
2.82
2.87		 EVENTS
} Setting up at observing site
} Setting up at observing site
} Setting up at observing site

First Contact





TOTALITY





Fourth Contact


Data sources :
High and low tide times   :Australian Bureau of Meteorology
Profile : http://tbone.biol.sc.edu/tide

Starting with the world map I zoomed in and selected Port Douglas.

The online tool allows you to generate a time interval height profile.  I generated this for 5 minute intervals from midnight EST on the 14th.  The data did not agree with the BOM data. It was out by about 10cm in high and low tide predictions and about 10 mins in time.

               TBONE                        BOM
LOW       02:15am   0.13m              02:31am    0.02m
HIGH      08:50am  2.88m             09:06am    2.98m 

I trust the BOM more and the tbone site contains a disclaimer warning that the data isn't guaranteed for accuracy.

I used the profile generated by the tbone site but renormalized the data to fit the BOM height predictions.  I didn't correct the 10 min time differences.  For the purposes of eclipse observation planning, they are insignificant.

Generating a set of heights is all very well but unless you can translate this to some sort of physical reality, it is of little use.  Along the Cairns -Port Douglas coast there are many beaches. Each beach has its own physical profile and this is the critical factor in determining how much real estate remains dry at high tide.

Many beaches in the region have very flat profiles. Consequently the higher king tides tides can come right up to the vegetation verge at the top of the beach. These vegetation verges frequently contain mangrove species which are highly salt tolerant.







However not all beaches are flat to the vegetation verge. Various beaches have different profiles and tides


        



One local tour guide told me that a 3m high tide can even wash into the carparks at Four Mile Beach. Four Mile Beach is very flat right into the treeline.   

The only way for anybody to get a definitive answer, is to use the high tides during the days before totality as a test to survey your observing site. The tides are a little lower and obviously at different times.

On eclipse day the estimated critical heights are -
06:40am       Totality             2.3m
07:00am       Partial               2.5m
07:40am       4th contact       2.7m

In the days before the eclipse there are several high tides which have the same heights as some of the listed eclipse day heights : -
Sun  10 Nov       06:24am        2.24m
Sun  11 Nov       07:00am        2.50m           18:55     2.55m
Mon 12 Nov       07:39am        2.72m           19:34     2.55m  
Tue 13 Nov       08:21am         2.89m           20:14     2.48m

Below is the raw data from http://tbone.biol.sc.edu/tide

The tbone site contains this discaimer
Web interface by Dean Pentcheff, calculations and graphics by David Flater's XTide Program

NOT FOR NAVIGATION. This program is furnished in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of merchantability or fitness for a particular purpose. Do not use this program as a basis for any decisions that could result in harm to people, other organisms, or property. Check these predictions against officially sanctioned tables. Agencies like NOAA exist because there is a need for certifiably correct tide predictions. Do not rely on these predictions if you need guaranteed results. There is NO WAY we can get certified data on a zero budget. We rely on users like you to tell us when something is wrong. Please continue to do so.
Remember that weather conditions affect tidal ranges and current speeds, sometimes very strongly.

Port Douglas, Australia
14 November 2012

2012-11-14  00:01 EST 0.733870
2012-11-14  00:06 EST 0.695261
2012-11-14  00:11 EST 0.657489
2012-11-14  00:16 EST 0.620595
2012-11-14  00:21 EST 0.584620
2012-11-14  00:26 EST 0.549605
2012-11-14  00:31 EST 0.515595
2012-11-14  00:36 EST 0.482637
2012-11-14  00:41 EST 0.450777
2012-11-14  00:46 EST 0.420068
2012-11-14  00:51 EST 0.390561
2012-11-14  00:56 EST 0.362313
2012-11-14  01:01 EST 0.335380
2012-11-14  01:06 EST 0.309822
2012-11-14  01:11 EST 0.285701
2012-11-14  01:16 EST 0.263078
2012-11-14  01:21 EST 0.242019
2012-11-14  01:26 EST 0.222587
2012-11-14  01:31 EST 0.204848
2012-11-14  01:36 EST 0.188865
2012-11-14  01:41 EST 0.174703
2012-11-14  01:46 EST 0.162422
2012-11-14  01:51 EST 0.152084
2012-11-14  01:56 EST 0.143746
2012-11-14  02:01 EST 0.137461
2012-11-14  02:06 EST 0.133279
2012-11-14  02:11 EST 0.131245
2012-11-14  02:16 EST 0.131401
2012-11-14  02:21 EST 0.133779
2012-11-14  02:26 EST 0.138408
2012-11-14  02:31 EST 0.145310
2012-11-14  02:36 EST 0.154500
2012-11-14  02:41 EST 0.165984
2012-11-14  02:46 EST 0.179761
2012-11-14  02:51 EST 0.195824
2012-11-14  02:56 EST 0.214157
2012-11-14  03:01 EST 0.234734
2012-11-14  03:06 EST 0.257524
2012-11-14  03:11 EST 0.282488
2012-11-14  03:16 EST 0.309576
2012-11-14  03:21 EST 0.338736
2012-11-14  03:26 EST 0.369905
2012-11-14  03:31 EST 0.403015
2012-11-14  03:36 EST 0.437992
2012-11-14  03:41 EST 0.474757
2012-11-14  03:46 EST 0.513225
2012-11-14  03:51 EST 0.553308
2012-11-14  03:56 EST 0.594913
2012-11-14  04:01 EST 0.637945
2012-11-14  04:06 EST 0.682305
2012-11-14  04:11 EST 0.727896
2012-11-14  04:16 EST 0.774617
2012-11-14  04:21 EST 0.822368
2012-11-14  04:26 EST 0.871048
2012-11-14  04:31 EST 0.920557
2012-11-14  04:36 EST 0.970799
2012-11-14  04:41 EST 1.021677
2012-11-14  04:46 EST 1.073098
2012-11-14  04:51 EST 1.124969
2012-11-14  04:56 EST 1.177205
2012-11-14  05:01 EST 1.229719
2012-11-14  05:06 EST 1.282431
2012-11-14  05:11 EST 1.335262
2012-11-14  05:16 EST 1.388139
2012-11-14  05:21 EST 1.440989
2012-11-14  05:26 EST 1.493747
2012-11-14  05:31 EST 1.546347
2012-11-14  05:36 EST 1.598729
2012-11-14  05:41 EST 1.650833
2012-11-14  05:46 EST 1.702604
2012-11-14  05:51 EST 1.753987
2012-11-14  05:56 EST 1.804930
2012-11-14  06:01 EST 1.855381
2012-11-14  06:06 EST 1.905291
2012-11-14  06:11 EST 1.954610
2012-11-14  06:16 EST 2.003287
2012-11-14  06:21 EST 2.051273
2012-11-14  06:26 EST 2.098517
2012-11-14  06:31 EST 2.144968
2012-11-14  06:36 EST 2.190572
2012-11-14  06:41 EST 2.235276
2012-11-14  06:46 EST 2.279023
2012-11-14  06:51 EST 2.321756
2012-11-14  06:56 EST 2.363416
2012-11-14  07:01 EST 2.403940
2012-11-14  07:06 EST 2.443267
2012-11-14  07:11 EST 2.481330
2012-11-14  07:16 EST 2.518065
2012-11-14  07:21 EST 2.553405
2012-11-14  07:26 EST 2.587280
2012-11-14  07:31 EST 2.619623
2012-11-14  07:36 EST 2.650366
2012-11-14  07:41 EST 2.679441
2012-11-14  07:46 EST 2.706781
2012-11-14  07:51 EST 2.732321
2012-11-14  07:56 EST 2.755997
2012-11-14  08:01 EST 2.777750
2012-11-14  08:06 EST 2.797523
2012-11-14  08:11 EST 2.815263
2012-11-14  08:16 EST 2.830920
2012-11-14  08:21 EST 2.844453
2012-11-14  08:26 EST 2.855822
2012-11-14  08:31 EST 2.864997
2012-11-14  08:36 EST 2.871952
2012-11-14  08:41 EST 2.876668
2012-11-14  08:46 EST 2.879134
2012-11-14  08:51 EST 2.879347
2012-11-14  08:56 EST 2.877310
2012-11-14  09:01 EST 2.873034
2012-11-14  09:06 EST 2.866540
2012-11-14  09:11 EST 2.857854
2012-11-14  09:16 EST 2.847009
2012-11-14  09:21 EST 2.834050
2012-11-14  09:26 EST 2.819023
2012-11-14  09:31 EST 2.801984
2012-11-14  09:36 EST 2.782997
2012-11-14  09:41 EST 2.762127
2012-11-14  09:46 EST 2.739449
2012-11-14  09:51 EST 2.715039
2012-11-14  09:56 EST 2.688980
2012-11-14  10:01 EST 2.661356

                                                   
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