The Denizens of the Norse World Tree, Yggdrasill

Quite a few years ago I included a chapter on Norse cosmology in my book THE TERRIBLE ONE'S HORSE:

https://ridingodinshorse.blogspot.com/2016/07/the-terrible-ones-horse-chapter-18.html

At the time, I neglected to investigate the nature of the various inhabitants of the world tree (or of its root).  In this piece I will attempt to redress that oversight.

EAGLE AND HAWK

At the very top of Yggdrasill, there is an ancient eagle.  Between his eyes sits a hawk, Vedrfolnir.  As the top of the tree is the Pole Star, upon which the sky turns, the hawk himself is Polaris.  The two eyes of the eagle are the stars Kochab and Pherkad of Ursa Minor 

"The only nearby bright stars that are readily seen are Kochab and Pherkad, which are also part of the Little Dipper. The two stars are known as the “Guardians of the Pole” because they appear to march around the North Star like sentries."

(https://www.constellation-guide.com/polaris-the-north-star/)

Thus it would appear that the eagle comprises, at least in part, the constellation of Ursa Minor.  

FOUR HARTS

Much has been written about the harts or stags of the tree.  Usually, they are compared with Saami celestial reindeer (or elk or moose).  But the number '4' in this context is important.  I take the harts to represent constellations that housed the equinoxes and solstices, and as being resident, therefore, on the ecliptic.  They divided the sky and the seasons into quarters.  They were said to be consuming the leaves of the world tree because the Sun, Moon and planets passed through them - actions that, in effect, symbolized the constant cycle of consumption and elimination.

SQUIRREL

Ratatosk is a tough one.  As he conveyed messages to the heavenly eagle and the underworld serpent, Nidhogg, he can't be anything moving along the ecliptic.  Nor can he represent a comet, which relative to earth seems slow-moving and does not conform to the image of an animal quickly running up and down a sky-tree.

As it happens, because of the difficulty in pinning down the squirrel, scholars usually default to this creature being a shamanistic spirit or spirit-guide.  However, that is putting the cart before the horse.  Before we can have such a being, we must first have a visual object with which it accords.  Lucky for us, the Ursid meteor shower literally originates at/very near the star Kochab in Ursa Minor, which as we've just seen is one of the eyes of the cosmic eagle.

https://www.timeanddate.com/astronomy/meteor-shower/ursids.html

https://www.skyatnightmagazine.com/advice/skills/ursid-meteor-shower-when-how-to-see-it/

The corollary must be found however, i.e. a meteor show with a radiant (point of origin) in Nidhogg.  In the past, I had made the case for Nidhogg being perhaps a lunar serpent.  But I may well have been wrong in this assessment.

The Draconids do originate from the head of Draco:

https://earthsky.org/astronomy-essentials/everything-you-need-to-know-draconid-meteor-shower/

But Draco is a circumpolar constellation in the Northern hemisphere and so never "descends" into the underworld.  

Could Nidhogg be Hydra, the great water serpent of Greek mythology?  Nidhogg is related to the many serpents that inhabit Hvergelmir, the 'Roaring Cauldron' that is the sea.  Two meteor showers originate in Hydra: in early December the active Sigma Hydrids and in January the minor Alpha Hydrids.

"The constellation Hydra, the sea serpent, is best seen from the southern hemisphere, but can be observed in the north between January and May."

http://www.seasky.org/constellations/constellation-hydra.html

From my Cybersky program, I have made this image of Hydra as seen from Iceland in March, down low above the southern horizon:

The Sigma Hydrids originate just above the head of Hydra. 

https://www.universeguide.com/meteorshower/sigmahydrids

Meteors can seem to rise upward into the sky, as well as plummet downward.  

From https://www.quora.com/In-a-meteor-shower-why-dont-we-see-the-meteors-rise-towards-the-sky-from-the-horizon:

"If the radiant is a bit below the horizon, then some meteors will be seen going upwards, with their trails pointing back to the radiant.

Have a look at this picture: Perseids Rain Like Fire From Space . Here, the radiant has risen a bit above the horizon, and you can see some meteors going "upwards" at the ten o'clock and two o'clock positions. If the photgrapher had pointed the camera higher, you'd see some going vertically.

Of course, they're all coming down from the perspective of the Earth as a whole. The "up" and "down" of individual meteor trails is just an effect of perspective as seen from a particular spot.

Perhaps the diagram here Vega marks Lyrid meteor radiant point | EarthSky.org might help. Imagine it's earlier in the night, and Vega and the radiant are just below the horizon. (Put a bit of paper across your computer screen if it helps, to simulate the horizon.) You'll see that most of the meteors visible at that time are on an "upward" path."

I would, therefore, argue that Ratatosk was representative of the meteors that appeared to pass between the eagle at Ursa Minor and those that rose from Hydra.

There comes the shadowy

dragon flying,

glittering serpent, up

from Dark of the Moon Hills.

He carries on his pinions

- he flies over the field -

Malice Striker [Nidhoggr], corpses.

VOLUSPA

Ursula Dronke translation

NOTE:  BOLVERK'S/ODIN'S AUGER RATI

Some scholars have sought to relate Ratatosk to the auger Odin uses to drill through a mountain in order to reach Gunnlod and the mead of poetry.  I do not think, however, that these two mythological symbols are the same.

My guess for Baugi's auger is the Milky Way, as seen when it was standing vertically over a distant mountain.  Here is a photo of this phenomenon:

The Milky Way does not "scamper" up and down the sky between the Pole Star and a constellation that spends most of the year below the horizon.  But it does stand in quite well for a sky-god's great drill, piercing down through the mountain into the interior of the earth.