A streak of light crossing the night sky, commonly called a shooting star, is actually a meteor—a piece of space debris entering Earth’s atmosphere. This debris, known as a meteoroid, is often no larger than a grain of sand. While meteors are often perceived as a single white or yellow flash, they display a spectrum of colors that reveal their origin and composition. The appearance of these colors depends on the material from the space rock and its interaction with the surrounding air.
The Science Behind the Glow
The brilliant glow of a meteor is not caused by combustion or “burning” in the traditional sense. Instead, the intense light is generated by the tremendous speed at which the meteoroid collides with air molecules in the upper atmosphere. Traveling at speeds up to 72 kilometers per second, the meteoroid creates a powerful wave of compressed air in front of it.
This rapid compression, known as ram pressure, heats both the air and the surface of the meteoroid to extreme temperatures, often thousands of degrees Celsius. The superheated air and the vaporized material from the meteoroid become ionized. This creates a glowing trail of plasma, which is the light we observe from the ground. The altitude where this process becomes visible, typically between 75 and 120 kilometers above Earth, marks the start of the meteor’s luminous flight.
Linking Specific Colors to Elements
The specific hue a meteor displays is a direct result of the chemical composition of the space rock. As the meteoroid material vaporizes, the atoms within it emit light at characteristic wavelengths, similar to how elements glow in a laboratory flame test.
A meteor rich in sodium will typically produce an orange or yellow-orange streak of light. Iron content in the space rock contributes to a bright yellow emission, while the presence of magnesium often results in a striking blue-green color. Less common is a violet or purple hue, which indicates a high concentration of ionized calcium within the meteoroid’s structure.
The atmosphere itself also contributes to the color display, especially for the longer-wavelength colors. As the surrounding air is heated by the passing meteor, excited nitrogen and oxygen atoms can emit a red light. Therefore, the overall color seen by an observer is a blend, determined by whether the light from the meteoroid’s metallic atoms or the ionized atmospheric gases is more dominant.
Factors Influencing Overall Brightness
While the color of a meteor is determined by its chemistry, its brightness is governed by separate physical factors. The primary factor influencing brightness is the initial mass, or size, of the meteoroid. A larger space rock contains more material to vaporize, leading to a much brighter flash of light.
The speed at which the meteoroid enters the atmosphere is the second major influence on its brightness. A faster meteor hits the air molecules with greater kinetic energy, generating significantly more heat and a brighter glow than a slower meteor of the same size. The angle of entry also plays a role; a shallow angle prolongs visibility but does not necessarily make the meteor as bright as a head-on impact.