# Tree Trunk Illusion: Does it Disappear Over the Horizon?

• Ryan Bruch
In summary, the conversation discusses the perceived disappearance of the lower part of a tree's trunk as an observer moves further away from the tree on a flat plane. However, it is clarified that this is not possible on a perfectly flat surface and the concept of a horizon only applies to curved surfaces such as the Earth. The conversation also mentions a thumb-rule from Nathaniel Bowditch's American Practical Navigator for estimating the distance to the horizon.

#### Ryan Bruch

Supposed there is a tree on a perfectly flat plane. If an observer in front of that tree moves further and further away from the tree, the tree would look smaller and smaller. When the observer moves further and further away, would the lower part of the tree's trunk seem to disappear as if sinking below the horizon?

No. Why would it?

davenn
A person claimed that it does and that he had observed it before, on Earth though. These are his illustrations:

Earth is curved, an oblate spheroid.

davenn
In more words, what Doug is telling you is that YOU were the one that specified a condition of a perfectly flat surface, thus, there is no such thing as a horizon. So, what is it? a flat surface or an sphere...please state your problem correctly and fully form the beginning.

davenn
In Nathaniel Bowditch's American Practical Navigator is listed a most useful thumb-rule for estimating the distance to the horizon for practical heights of eye.

## 1. What is the "Tree Trunk Illusion"?

The "Tree Trunk Illusion" refers to a phenomenon where a tree trunk appears to disappear as it reaches the horizon.

## 2. Why does the tree trunk appear to disappear over the horizon?

This illusion occurs due to the curvature of the Earth. As the tree trunk gets farther away, the curvature of the Earth makes it appear as though the tree is disappearing over the horizon.

## 3. Does the "Tree Trunk Illusion" only happen with tree trunks?

No, this illusion can happen with any object that is tall and extends above the horizon. This can include buildings, mountains, or even people standing on a high platform.

## 4. Can this illusion be observed in different locations and environments?

Yes, this illusion can be observed in any location with a visible horizon, such as a beach, open field, or even in a city with tall buildings.

## 5. Is the "Tree Trunk Illusion" a real optical illusion or just a trick of the mind?

This is a real optical illusion caused by the curvature of the Earth. It is not a trick of the mind, but rather a result of how our eyes perceive objects in relation to the Earth's curvature.