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Abel Tasman's actual vs estimated position on Dec 13th 1642.

Abel Tasman’s actual vs estimated position on Dec 13th 1642.

On December 13th 1642, Abel Tasman was nowhere near where he thought he was.

While Tasman’s Latitude was correct, his longitude estimation between Tasmania and New Zealand was wrong by over a degree.

In his journal entry for 14th December Tasman wrote something that exposed this error.

He described being so close to the coast that he could see the surf breaking, yet according to his longitude estimate he was still 150 km from the nearest land.

At noon on 14th of December Tasman also put this in his journal; “At noon Latitude observed 42° 10′, Longitude 189°3′; course kept east, sailed 12 myles. We were about 2 myles off the coast.” (a Dutch ‘myle’ is one fifteenth of a degree of latitude, or 7.4km).

This allows us to reconstruct exactly where he was at noon on Dec 13th.

Abel Tasman's actual vs estimated position on Dec 13th 1642.

Abel Tasman’s actual vs estimated position on Dec 13th 1642.

He was 2 myles off the coast, and had sailed directly east 12 myles since the previous day… and for that day, Tasman had been able to make a sighting of the midday sun; and he recorded an ‘observed’ latitude 42° 10’s.

At midday on December 13th 1642, Abel Tasman was in the latitude 42° 10’s, 104 km off the coast, and heading south east towards ‘large, high-lying land’. The land was ‘at about 15 myles distance’; approximately 110 km.

So what was the high land had had seen and was sailing towards?

This analysis shows which land was visible to Tasman from his location at noon.

Geographic analysis of the land visible to Abel Tasman from his noon position on Dec 13th.

Geographic analysis showing the land visible to Abel Tasman from his noon position on Dec 13th.

The peaks nearer the coast, Mt Camelback and Mt Grahem were visible to him, but at 561m and 828m respectively they were very low on his horizon and most likely lost in the surface haze.

Most of his skyline was formed by the line of peaks in the middle distance; Cairn Peak (1,859), Mt Reeves (1,783m), Mt O’Connor (1,815m) and Mt Bowen (1,985). Tasman wrote that he saw land about 15 myles away, and this line of peaks is 17 ½ myles from his noon position.

The distant skyline filled the gaps between these peaks and comprises mountains at the northern end of the Southern Alps, including Mt Murchison (2,400m) and Urquarts Peak (2,118m). These peaks form a slightly higher horizon, but are further away; nearly 20 ‘myles’.

Abel Tasman could have seen the biggest peaks in the Southern Alps; Mt Cook and Mt Tasman. They were well above his horizon, and even though Mt Cook (3754m) was 160 km away, it’s perfectly possible to see it from this distance in favourable conditions.

Mount Cook seen from  Fourteen Mile beach, 140km away

Mount Cook seen from Fourteen Mile beach, 140km away

From his actual position on 13th December he could have seen Mt Cook and Mt Tasman; the biggest peaks in the Southern Alps, but he could not have seen them to his south east. If he had seen them, he would have recorded seeing them to his south-south-west.

When Tasman saw a ‘large, high-lying land’, he was not looking at that snow capped peak that now bears his name, but at Mount O’Connor, Mount Reeves, and Cairn Peak.

The first 'high land' that Abel Tasman saw.

The first ‘high-lying land’ that Abel Tasman saw.

This, is the ‘high-lying land’ that was seen by Abel Tasman.

The main peak appearing south east of Abel Tasman on Dec 13th 1642 was Mt O’Connor, 1,815m.

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