Question

A star emits light of $5500$ wavelength. It appears blue to an observer on the earth, it means?

Answer 1

Let us first get some idea about wavelength. The wavelength is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests, troughs, or zero crossings, in physics. It is a feature of both travelling waves and standing waves, as well as other spatial wave patterns.

Complete step-by-step solution:
The spatial frequency is the inverse of the wavelength. The Greek letter lambda ($\lambda$) is widely used to represent wavelength. Modulated waves, as well as the sinusoidal envelopes of modulated waves or waves created by the interference of numerous sinusoids, are sometimes referred to as wavelengths.
A wave's wavelength is determined by the medium through which it travels (for example, vacuum, air, or water). Sound waves, light waves, water waves, and periodic electrical signals in a conductor are all examples of waves. A sound wave is a change in air pressure, whereas the intensity of the electric and magnetic fields varies in light and other electromagnetic radiation. Variations in the height of a body of water are known as water waves. Atomic locations change in a crystal lattice vibration.
The wavelength of blue radiation is roughly $4600$ wavelength. It demonstrates that the apparent wavelength is less than the true wavelength. It indicates that the star is moving closer to Earth.

Note:
A spectrum is a collection of wavelengths or frequencies used to describe wave events. The term was first used to describe the visible light spectrum, but it is now used to describe the full electromagnetic spectrum, as well as a sound or vibration spectrum.