The Comet's Tail and Its Various Phenomena

133. The Comet’s Tail and Its Various Phenomena

Comets exhibit a long, radiant tail, which gives them their name.

This tail is always seen on the side roughly opposite to the Sun. So, if the Earth is positioned in a straight line between the comet and the Sun, the tail appears to spread in all directions around the comet.

For instance, the comet of 1475 displayed a tail when it was first seen. By the end of its appearance, it trailed its tail behind it as it was in the opposite region of the sky.

This length of this tail depends on several factors:

1. The size of the comet

Small comets have no tail. Large ones can appear very small when receding from our view.

2. Location

All else being equal, the the tail appears longer the farther the Earth is from a straight line drawn from the comet to the Sun.

Sometimes, when the comet is hidden under the Sun’s rays, only the tip of its tail, resembling a fiery beam, is visible.

Lastly, the tail can sometimes be wider or narrower, straight or curved, and sometimes directly opposed to the Sun or not precisely so.

134. This Tail Depends a Certain Refraction

The comet’s tail is caused by a new type of refraction. I did discuss this in Dioptrics because it is not observed in terrestrial bodies.

This refraction arises because air-aether globules are not all equal in size. Instead, they gradually diminish from the sun’s territory from Saturn to the Sun itself.

This results in light rays which pass through the larger globules. These rays go in straight lines but are also refracted and scattered to the sides by the smaller globules.

135. Explanation of This Refraction

Let there be many very small globules surrounded by much larger ones. All are in continuous motion, as described for air-aether globules.

If A is pushed towards B, its action is communicated immediately to all those found in a straight line from it in that direction.

• Notably, the action reaches from A to C intact.
• But a part of it can also pass from C to B.
• The rest is dispersed towards D and E.

The globule C cannot push globule 2 towards B without also pushing globules 1 and 3 towards D and E.

The action from A to C is deflected towards D and E by the globules 4 and 5. But it still tends directly towards C.

The continuous motion ensures that this action is never intercepted by two at once but only successively by one and then the other.

When globule C pushes three globules 1, 2, 3 towards B, its action cannot be remitted to just one of them, and some always intercept this action obliquely.

Therefore, the principal ray proceeds directly towards B. But innumerable weaker rays are dispersed to the sides towards D and E.

Similarly, if globule F is pushed towards G, its action, when reaching H, is communicated to globules 789. This sends the principal ray to G and dispersing others towards D and B.

Note the difference caused by the obliquity of the incidence of these actions on circle CH.

• The action from A to C, incident perpendicularly on the circle, disperses its rays equally towards D and E.
• The action from F to H, incident obliquely on the same circle, disperses its rays only towards its center.

If the obliquity is 90 degrees, the rays are not sent to the other side except as much weaker ones, unless the obliquity is very small.

Conversely, rays obliquely scattered towards the center of the circle are stronger the greater the obliquity.

136. Explanation of the Comet’s Tail Appearance

We apply this demonstration to air-aether globules.

There is no place for the larger globules to immediately replace the much smaller ones.

Yet, the difference between those beyond Saturn’s orbit and those near Earth’s orbit is similar to the described difference between larger and smaller globules.

Therefore, the effect of this inequality on Earth’s orbit should be the same as if the smallest globules immediately followed the larger ones, except that the lines along which these rays are dispersed are not straight but gradually curved.

Let S be the Sun.

• Circle 2345 is the Earth’s counterclockwise orbit
• DEFG is the territorial boundary where the air-aether globules between the large globules near Saturn and the small globules near the Sun

C is a comet in our solar system. The Sun’s rays striking this comet are reflected towards all parts of the spheroid DEFGH. Those perpendicular to F mainly go straight to 3 but are also scattered sideways.

Rays obliquely striking G go straight to 4 but are also refracted towards 3.

Those hitting H do not reach Earth’s orbit directly but are reflected towards 4 and 5, and so forth.

Thus, if Earth is at 3, this comet will appear from there with its tail spread in all directions.

This type of Comet they call a Rose.

• The direct rays from C to 3 form its head.
• The weaker ones, which are reflected from E and G towards 3, will show its hair.

But if the Earth is in 4, the same Comet will be seen through the straight rays CG4. Its coma, or rather tail, extends towards only one part, through rays from H and other places between G and H reflected towards 4.

If the Earth is at 2, the Comet will be seen by the straight rays CE2. Its coma will be seen by the oblique ones, which are between CE2 and CD2.

There will be no difference except that:

• with the eye at 2, the Comet will be seen in the morning, and its coma will precede it.
• with the eye at 4, the Comet will be seen in the evening, and it will drag its tail behind it.