If you see a red-hot star, you can be certain that that its peak intensity is in the ingrared region. Why is this? And if you see a violet-hot star, you can be certaiin its peak intensity is in the ultraviolet range. Why is this?

The human eye is not very sensitive to red or violet. So if you see red or violet as the predominant spectrum, its intensity is very high.

The color and temperature of a star are closely related to its peak intensity of radiation. This relationship is explained by Wien's law, which states that the peak wavelength of radiation emitted by an object is inversely proportional to its temperature.

1. Red-Hot Star:
When you see a red-hot star, it indicates that its peak intensity is in the infrared region. This is because red light has a longer wavelength compared to other colors in the visible spectrum. According to Wien's law, objects with lower temperatures have longer peak wavelengths. Therefore, the red-hot star has a lower temperature than stars emitting light in other colors, which results in its peak intensity occurring in the infrared range.

2. Violet-Hot Star:
If you observe a violet-hot star, it suggests that its peak intensity is in the ultraviolet range. Violet light has a shorter wavelength compared to other visible colors. Higher temperatures result in shorter peak wavelengths according to Wien's law. Therefore, the violet-hot star has a higher temperature than stars emitting light in other colors, causing its peak intensity to occur in the ultraviolet region.

To understand why a red-hot star has its peak intensity in the infrared region while a violet-hot star has its peak intensity in the ultraviolet range, we need to delve into the science behind black body radiation and Wien's displacement law.

Black body radiation is the electromagnetic radiation emitted by an object due to its temperature. According to Wien's displacement law, the wavelength at which a black body radiates most intensely is inversely proportional to its temperature. This means that hotter objects emit radiation with shorter wavelengths, while cooler objects emit radiation with longer wavelengths.

Now let's apply this concept to the stars. Stars are massive, glowing balls of gas, primarily composed of hydrogen and helium. The surface temperature of a star determines the color of its emitted light. The temperature range of stars is quite vast, ranging from a few thousand degrees to tens of thousands of degrees Celsius.

When a star appears red-hot, it means its surface temperature is relatively lower. In this case, the star emits most of its radiation in the longer wavelength range, which includes the infrared region. The maximum intensity of the emitted light occurs at a wavelength corresponding to the peak of the infrared range. Therefore, when we see a red-hot star, we can be certain that its peak intensity is in the infrared region.

On the other hand, when a star appears violet-hot, it indicates a much higher surface temperature. A hotter star emits radiation with shorter wavelengths, including the ultraviolet region. The peak intensity of the emitted light for a violet-hot star occurs at a wavelength corresponding to the ultraviolet range. Hence, when we see a violet-hot star, we can be certain that its peak intensity lies in the ultraviolet range.

In summary, the color of a star is directly related to its surface temperature. Lower temperature stars appear red-hot with peak intensity in the infrared region, while higher temperature stars appear violet-hot with peak intensity in the ultraviolet range. This pattern follows from the principles of black body radiation and Wien's displacement law.