As on the thread pattern page, we're going to consider two possible Perns with circumferences of (A) 20,400 miles (B) 4,500 miles.
DLG says "at sea level, Thread is visible on the horizon thirty minutes before it will be overhead". That might be (A) derived data, I can't find it in the books. Let's check it out.
Thread separates from its pods at 15,000 ft.
The distance to a horizon on a planet is given by the formula
d = (h*c)^0.5
where h is the height of the observer and c a constant dependent on the size of the planet.
If h is in feet and d in miles then for Earth c=1.5. Using a bit of trigonometry this constant can be derived for our planets: (A) 1.22 (B) 0.269.
Calculate for the observer and the Thread cloud and add the two together:
(A) 141 miles (B) 65 miles
Assuming totally flat ground and a 6' tall Menolly.
|Varying the distance to the horizon produces odd visual effects. Prior to space exploration SF writers could only surmise as to how the human brain might react, but look at this photo. Rover has landed on a flat boulder strewn plain with low hills on the horizon centre right. Mars being smaller than Earth (circumference 13,263 miles) the horizon is closer and the ground appears to our eyes to be rising.|
From the Thread page we have the speed of the Thread cloud:
(A) 340 mph (B) 75 mph
She could have spotted it with at most (A) 25 mins (B) 51 mins to spare, but it's the dragons flaming she sees and their fighting ceiling is around 10,000 ft according to DLG. 1
So, at 10,000 ft dragons are seen at
(A) 38 miles (B) 18 miles
which is (A) 7 minutes (B) 14 minutes away
Menolly can see the Dragon Stones on the horizon (12ft below horizon?), so she is about (A) 6.5 (B) 3 miles from her cave. At about 8 mph she can make that in (A) 48 mins (B) 22 mins. Oh dear.
I've been fudging figures a lot, but it looks as though (B) is a better fit. Menolly in (B) was within safety range if she'd kept a better lookout - she's not that stupid - whereas with (A) she would never have seen the Thread cloud in time.
If you believe in four hour Threadfalls then times reduce by 2/3rds. This gives a maximum Thread warning time of (B) 34 minutes, close to the DLG figure - but only gives Menolly (B) 10 minutes running time!
Are you in land of known economic value? If you are, good news - the dragonriders will be trying to protect it.
Can you see dragons flaming? Bad news - you should have seen the Thread cloud earlier. If no shelter is known about or visible within a couple of miles, run towards valuable land.
You can't outrun Thread. But you might be able to get out of its way: take a good look at the cloud and try to determine the nearest side edge. Now run towards it, parallel to the leading edge. You should make at least a couple of miles before it arrives in open country.
If you spot water you can submerge in, do so as the fall reaches you.
Hold something over your head that you can throw away if Thread hits it.
Failing all else keep running, being upright makes you a smaller target and more visible.
If you smell fire and brimstone, stop. You are either about to fall into a volcano (bad idea) or rescue is at hand. Be prepared to put up with a lecture on crass stupidity, doubly so if your savior is an Old-Timer.
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