There are many Spiders of Bigness, each bigger than an island of Cyclades, which weave a web so the Moon can go to war with the Sun. The smallest of the islands of Cyclades is Donousa, which has a width and length of 5km (or 5000m).
M2 = (H2/H1)^3*M1
= (5000/0.12)^3*0.01048932
= 7.58776042e11kg
We have our weight...but how to find out speed. For an absolute low end minimum, the worlds fastest spider (the camel spider) can move at 16km/h (.
KE = (0.5)mv^2
= (0.5) X 7.58776042e11 X 4.44444444^2
= 7.49408435e12 joules
= 1.791129146749522 kilotons
This is a colossal lowball though, as we know they can move far faster than this. The web between the Moon and the Morningstar was spun in an instant, which while fast, is unfortunately vague. Thankfully, we have other methods we can use to find a minimum. A huntsman can move between 30 to 40 body lengths in a second.
L = 5km X 30
= 150km
T = 150km/1s
= 150000/340.29
= Mach 440.800494
KE = (0.5)mv^2
= (0.5) X 7.58776042e11 X 150000^2
= 8.53623047e21 joules
= 2.0402080473231358759 teratons
Otherwise, the badge huntsman can travel 16 times its own body length in a second.
L = 5km X 16
= 80km
T = 80km/1s
= 80000/340.29
= Mach 235.093597
KE = (0.5)mv^2
= (0.5) X 7.58776042e11 X 80000^2
= 2.42808333e21 joules
= 580.32584369024857551 gigatons
That's one method of finding our speed, but just in case, let's also go for another, using the distances of Ancient Greek cosmologists for the Solar System. Posidonius calculated the circumference of the Earth to be 38,647km.
R = π/C
= 38647/π
= 12301.7222/2
= 6150.8611km
According to Hipparchus, if 1 radii was a radius of the Earth, then the Moon was calculated to be 72 radii from the Earth at it's furthest, and 490 radii from the Sun.
On Sizes and Distances (Hipparchus) - Wikipedia
en.wikipedia.org
L = 6150.8611km X 490
= 3013921.94km
L = 6150.8611km X 72
= 442861.999km
L = 3013921.94km - 442861.999km
= 2571059.94km
That's the distance, so how do we get a timeframe? Thankfully, A True Story gives us a timeframe to work with. Lucian says that he was taken alive back to the Sun as a prisoner the next day, meaning the entire main battle took place in a day. This gives us a timeframe of 24 hours.
T = 60 X 60 X 24
= 86400s
T = 2571059.94km/86400s
= 29757.6382/340.29
= Mach 87.4478774
If that's not enough, we can also get the kinetic energy. Each Nephelocentaur's human parts equals the Colossus of Rhodes, which was 33m tall (they technically are centaurs, but I can't be bothered mathing that out; it will be higher than just a giant human in anycase). The average weight of a Greek Man is 88.1kg, with an average height of 177cm (1.77m).
M2 = (H2/H1)^3*M1
= (33/1.77)^3*88.1
= 570949.805kg
KE = (0.5)mv^2
= (0.5) X 570949.805 X 29757.6382^2
= 2.52792888e14 joules
= >60.4189502868068828 kilotons
Alternatively, we can use the calculations of Aristarchus, that being 20 radii to the Moon from Earth and 380 radii from the Earth to the Sun.
L = 6150.8611km X 20
= 123017.222km
L = 6150.8611km X 380
= 2337327.22km
L = 2337327.22km - 123017.222km
= 2214310km
T = 2214310km/86400s
= 25628.588/340.29
= Mach 75.3139616
KE = (0.5)mv^2
= (0.5) X 570949.805 X 25628.588^2
= 1.87506917e14 joules
= >44.8152287284894868 kilotons
Finally...we know that the astrological distances of the Solar System are bigger than calculated back then (though ancient mathematicians and philosophers where surprisingly close). I don't think the Ancient Greeks would mind if we used modern values... The distance from Earth is 252170000km, while the distance from the Moon to the Earth is 384,000km, and the distance from the Sun to the Earth is 147620000km.
L = 252170000km - 384,000km
= 251786000km
T = 251786000km/86400s
= 2914189.81/340.29
= Mach 8563.84205
KE = (0.5)mv^2
= (0.5) X 7.58776042e11 X 2918634.26^2
= 3.23178876e24 joules
= 772.41605162523910622 teratons
L = 147620000km - 384,000km
= 147236000km/86400s
= 1704120.37/340.29
= Mach 5007.84734
KE = (0.5)mv^2
= (0.5) X 570949.805 X 1704120.37^2
= 8.29026606e17 joules
= 198.14211424474186174 megatons
Final Results
Giant spiders speed (low end) = Mach 235.094
Giant spiders speed (mid end) = Mach 440.800
Giant spiders speed (high end) = Mach 8563.842
Giant spiders kinetic energy (low low end) = 1.791 kilotons
Giant spiders kinetic energy (high low end) = 580.326 gigatons
Giant spiders kinetic energy (low high end) = 2.040 teratons
Giant spiders kinetic energy (high high end) = 772.416 teratons
Nephelocentaurs speed (low end) = Mach 75.314
Nephelocentaurs speed (mid end) = Mach 87.448
Nephelocentaurs speed (high end) = Mach 5007.847
Nephelocenaurs kinetic energy (low end) = >44.815 kilotons
Nephelocentaurs kinetic energy (low end) = >60.419 kilotons
Nephelocentaurs kinetic energy (high end) = >198.142 megatons
Hopefully I did all this right. A lot of the information is literally millenia old, but it shows even back then all of this was insanely impressive.