First sunlight in "mainland" tasmania

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First sunlight in "mainland" tasmania

Postby cnschulz » Fri 02 Nov, 2018 7:15 pm

Gday,

Does anyone know (or know how to calculate) where the suns rays first hit the ground in Tasmania. This article: http://www.abc.net.au/science/articles/ ... /23507.htm suggests "some peaks in south east Tasmania" but is not specific. For bonus points, the last place the sun visits would be great too. Im thinking of doing "the longest day" challenge! :)
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Re: First sunlight in "mainland" tasmania

Postby ILUVSWTAS » Fri 02 Nov, 2018 7:42 pm

Geez I'm not even sure how you would work this out... maybe mt Graham or mt Maria for the sunrise and mt Sorell or Jukes for sunset.?

Just a complete guess there though.
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Re: First sunlight in "mainland" tasmania

Postby scrub boy » Fri 02 Nov, 2018 8:30 pm

I recall from 2000 the first sun is seen from Mt La Perouse; go as far south as you can and then go as high you can......
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Re: First sunlight in "mainland" tasmania

Postby GPSGuided » Fri 02 Nov, 2018 9:42 pm

Between going south and going high, which one dominates?
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Re: First sunlight in "mainland" tasmania

Postby Mark F » Fri 02 Nov, 2018 11:07 pm

A few bits of information can help answer the question.
- At 43 degrees south sunrise moves e-w across the landscape at touch over 20 kilometers per minute.
- At around 43 deg south, moving 30km further north delays sunrise by 1 minute.
- A bit of Google-fu found a table that shows the distance to the horizon from different heights above sea level http://www.table-references.info/earth-table-distances.php.

I initially thought La Perouse (1158m) seemed a good possibility but somewhere like Mt Fortescue (480m) on the Tasman Peninsula could be better than La Perouse. A quick measure shows Mt Fortescue is 100km east of La Perouse and only 36km further north. THe elevation difference is in favour of La Perouse by 1.5 minutes but the easterly advantage of 5 minutes goes to Mt Fortescue and it loses only a minute due to being further north - so about 2.5 minutes ahead of La Persouse. I checked this using the Geoscience Australia calculator http://www.ga.gov.au/bin/geodesy/run/sunrisenset Mt Fortescue comes out 4 minutes in front with Adamsons Peak showing the same sunrise/sunset times as La Perouse. This calculator doesn't seem to allow for elevation reducing the 4 minutes by 1.5 minutes to allow for the elevation difference has both calculations matching.
I also calcuated a couple of others:

Another that is close by - Adamsons Peak ( 67m higher, 6km further east, 17km further north) The 67m height adds 29km to the horizon distance + 6km north - same as La Perouse.

Mt Freycinet (620m) compared to Mt Fortescue gains 2 minutes due to extra elevation plus 1 minute for being further east but loses 3 minutes being further north - so a tie.

Mt Elephant (757m) doesn't quite make it even though it is 280m higher than Mt Fortescue (Gains 3 minutes on greater elevation plus 1 minute on 25km further east but loses 6 minutes for being 172km further north).

While these values are rough they show that there could be a few contenders for the sunrise title.
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Re: First sunlight in "mainland" tasmania

Postby GPSGuided » Fri 02 Nov, 2018 11:44 pm

Mark, you win!
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Re: First sunlight in "mainland" tasmania

Postby Mark F » Sun 04 Nov, 2018 8:35 am

For sunset I need to do the calcs but it is exactly the same process and values. My quick guess is Mt Sorell (1144m) after a scan of the map.

Edit. I built a little spreadsheet to test places. The best I have come up with is the high point (690m) on the South West Cape Range which loses the light 1 minute after Mt Sorell with Mt Hean (749m) in the De Witt Range only 6 seconds behind.
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Re: First sunlight in "mainland" tasmania

Postby MrWalker » Sun 04 Nov, 2018 2:27 pm

So now we need to know if anyone can get the "longest day" in Tasmania by starting on top of Fortescue or Freycinet at sunrise, then rushing across to Mt Sorrell by Sunset.
The Abels book says it takes 7hrs each way for Mt Sorell, starting from the Road to Kelly Basin. Is there time to drive to that carpark after starting on either of the two over east?
Google Maps says about 6 hrs driving from either the Freycinet or Fortescue car park to the Mt Sorell walk start, so 13 hrs taken up so far.
Hobart gets 15 hr 21 min of daylight on 22 December, so if you can get from the top of Freycinet or Fortescue in less than 2 hrs 20min then it will be worth doing to try to get more daylight than if you just sat at home all day. :roll:
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Re: First sunlight in "mainland" tasmania

Postby bernieq » Sun 04 Nov, 2018 9:45 pm

Have you considered the angle of the terminator? At solstice, the terminator is at approx 23.5deg to the Earth's axis.

In southern hemisphere summer, on the same longitude, a point further south has dawn before a more northly point.
Last edited by bernieq on Mon 05 Nov, 2018 8:45 pm, edited 4 times in total.

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Re: First sunlight in "mainland" tasmania

Postby Mark F » Mon 05 Nov, 2018 7:50 am

It seems counter intuitive but the azimuth of sunrise (and sunset) are well below 90 deg at the summer solstice. ga has a calculator for the position of the sun and moon so you can calculate it for any date and time http://www.ga.gov.au/bin/geodesy/run/sunmoonposn

The results for Hobart on the solstice. I had to enter a time (5:30) so it shows a little after sunrise (Altitude 4')

HOBART Lat=-42°53'00" Long=+147°17'00" Height=0.0m

AZIMUTH AND ALTITUDE OF THE SUN
Time zone: +11.00 hours
Altitude includes astronomical refraction angle for a standard atmosphere.
Date Time Refraction Azimuth Altitude
22/12/2018 05:30:00 00°34'00" 123°34'32" 0°04'00"

Computed using National Mapping Division's sunmoonposn program, version 1.1

Azimuth is the clockwise horizontal angle (in degrees minutes and seconds)
from true north to the sun/moon.
Altitude is the vertical angle (in degrees minutes and seconds)
from an ideal horizon, to the sun/moon.
An ideal horizon exists when the surface forming the horizon is at a
right angle to the vertical line passing through the observer's position on the earth.
If the terrain surrounding the observer was flat and all at the same height above sea level,
the horizon seen by the observer standing on the earth would approximate the ideal horizon.
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Re: First sunlight in "mainland" tasmania

Postby GPSGuided » Mon 05 Nov, 2018 12:05 pm

Just dawned from Mark’s post above, Tasmania’s latitude doesn’t even reach 45 deg S, not even half way to 90. And it’s already at the southern most point of Australian states.
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Re: First sunlight in "mainland" tasmania

Postby bernieq » Mon 05 Nov, 2018 8:58 pm

Mark F wrote:the azimuth of sunrise (and sunset) are well below 90 deg at the summer solstice

By "below", you mean further south? ie greater than 90deg.

Just to be clear, in the southern hemisphere at the summer solstice, the sun rises south of east - 123deg as calculated by mark f

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Re: First sunlight in "mainland" tasmania

Postby Mark F » Tue 06 Nov, 2018 6:50 am

Sloppy wording on my part - Bernie's words are correct.
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Re: First sunlight in "mainland" tasmania

Postby cnschulz » Wed 07 Nov, 2018 9:40 am

This is amazing information! Im glad I asked. I thought the collective would have know the answer already!
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