Introduction:
The temperature of the sun's rays varies depending on the angle at which they hit the Earth's surface. Vertical rays, which strike the surface perpendicularly, tend to be hotter than slanting rays. This can be attributed to several factors that influence the amount of solar energy absorbed by the Earth's surface.

1. Solar Intensity:
The intensity of solar radiation is higher when the sun is directly overhead, resulting in hotter temperatures. Vertical rays have a shorter path to travel through the atmosphere, encountering less scattering and absorption of solar energy. This allows a larger amount of energy to reach the Earth's surface, leading to increased heating.

2. Surface Area and Concentration:
Vertical rays cover a smaller surface area compared to slanting rays, allowing the same amount of solar energy to be concentrated on a smaller region. This concentration of energy per unit area results in higher temperatures. Conversely, slanting rays cover a larger surface area, causing the same amount of energy to be dispersed over a larger region, resulting in lower temperatures.

3. Atmospheric Path Length:
The angle at which the sun's rays enter the Earth's atmosphere affects the distance they must travel through it. Vertical rays have a shorter path length through the atmosphere compared to slanting rays. This reduced path length minimizes the opportunity for energy to be absorbed or reflected by the atmosphere, allowing more energy to reach the surface and contribute to heating.

4. Absorption and Reflection:
When sunlight enters the Earth's atmosphere at a slanting angle, it encounters a greater amount of atmospheric particles, such as dust, water vapor, and pollutants. These particles can scatter and absorb solar energy, reducing the amount that reaches the surface and subsequently lowering the temperature. In contrast, vertical rays pass through a shorter distance of the atmosphere, encountering fewer particles and experiencing less scattering and absorption.

Conclusion:
In summary, vertical rays of the sun are hotter than slanting rays due to their higher solar intensity, concentration of energy, shorter atmospheric path length, and reduced absorption and reflection. These factors collectively contribute to a greater amount of solar energy reaching the Earth's surface and causing increased temperatures.