The Perseid meteor shower is coming! Why do meteors have different colors?

Produced by: Science Popularization China

Author: Denovo Team

Producer: China Science Expo

The Perseid meteor shower is one of the most famous and active meteor showers each year, usually appearing from mid-July to late August, with its peak usually between August 12 and 14.

The Perseid meteor shower is so called because its radiant point (the point in the sky where the meteors appear to originate) is in the direction of the constellation Perseus. Originating from Comet 109P/Swift-Tuttle, the Perseid meteor shower can produce 60 to 100 meteors per hour, making it one of the most popular astronomical phenomena in the summer night sky due to its fast speed, high brightness and obvious tails.

Meteor Showers

(Image source: generated by the author’s AI)

Why do shooting stars come in different colors?

Meteors appear in different colors because their composition is heated by the intense heat as they enter the Earth's atmosphere, causing various elements and compounds to burn and emit specific spectra.

When meteoroids enter the Earth's atmosphere, they collide violently with a large number of air molecules. These collisions cause the material on the surface of the meteoroid to vaporize due to high temperatures, forming vapors of atoms such as sodium, iron and magnesium.

In the subsequent collision, the electron is knocked into an orbit at a greater average distance from the nucleus. When the electron falls back to its resting position, it emits light, the same process that creates a gas-discharge lamp.

Meteors of different compositions burn at high temperatures to produce light of different colors, which is similar to the flame color reaction we learned in middle school . In the flame color reaction, metal salts burn at high temperatures to produce specific colors, which is also the basis of flame analysis. For example:

Sodium (Na): yellow

Magnesium (Mg): blue-green

Calcium (Ca): purple

Iron (Fe): yellow to orange

Silicon (Si): red or orange

When a meteor enters the Earth's atmosphere, in addition to the meteor itself, its high-speed motion causes violent collisions with nitrogen (N2) and oxygen (O2) molecules in the air. The energy generated by these collisions excites and ionizes the nitrogen and oxygen molecules, causing them to emit light. Excitation refers to the absorption of energy by the electrons of a molecule, which transitions from the ground state to the excited state. Ionization refers to the absorption of enough energy by the electrons of a molecule to break away from the molecule and form ions. For example, the combustion of oxygen produces green or red light, while the combustion of nitrogen produces purple light.

Why does the same meteor change color?

In the Perseid meteor shower in August 2023, the author saw a fireball that changes color. Fireballs are extremely bright meteors, with brightness usually reaching or exceeding -4 magnitude, significantly brighter than ordinary meteors. Fireballs usually last for a long time, have a variety of colors, and may explode, even accompanied by loud sonic booms and scattered debris.

Color-changing fireball

(Photo credit: Photo taken by the author)

The color change of a meteor can be affected by other factors, such as the speed at which the meteor enters the Earth's atmosphere, the altitude at which it is located, and the size of the meteor. These factors work together to determine the specific color change that a meteor exhibits as it burns.

A fireball

(Image source: generated by the author’s AI)

1. Different ingredients

Meteors are usually composed of a variety of elements and compounds, and different components burn at high temperatures to emit different colors. For example, one part of a meteor may be rich in magnesium, while another part may be rich in sodium. When the meteor burns, these different components emit blue-green and yellow light respectively.

2. Changes in combustion temperature

As a meteor accelerates through the atmosphere and is affected by air resistance, its burning temperature changes. Burning at different temperatures causes the spectra of different elements or compounds to change. For example, at relatively low temperatures, the yellow light of sodium may be dominant, while at higher temperatures, the blue-green light of magnesium may appear.

3. Changes in atmospheric density

As a meteor enters the Earth's atmosphere, it moves from the thinner atmosphere at high altitudes to the denser atmosphere at low altitudes. Changes in atmospheric density affect the burning process and luminous characteristics of a meteor. At higher altitudes, the burning may be incomplete, and some components may emit light of one color; while at lower altitudes, the atmospheric density increases, the burning is more intense, and another color may be emitted.

Observation Guide

The Perseid meteor shower is coming, which is one of the most spectacular astronomical phenomena every year. Let's look up at the starry sky on a special night and enjoy the beautiful sight of meteors streaking across the sky. The following is an observation guide prepared for everyone, hoping to bring you the best viewing experience.

Watching shooting stars

(Image source: generated by the author’s AI)

Best time to observe : August 12-14, 2024 Due to the influence of the moon, midnight to a few hours before dawn is the best time to observe the Perseid meteor shower. The moon will set at 23:28 on the 12th; the moon will set below the horizon at 00:09 on the 13th; and the moon will set below the horizon at 00:57 on the 14th, because you can choose 1-2 hours before the moon sets.

Observation location selection : Stay away from urban light pollution. It is best to drive to a place with a wide view and darkness more than 100 kilometers away from the city, such as a rural area or a mountain top. Make sure the weather is clear and cloudless for the best observation effect.

Preparation : Bring a reclining chair or blanket so you can lie down comfortably and gaze up at the night sky. Bring enough clothing to keep warm, as well as mosquito repellent and a Bluetooth speaker.

Observation tips : It is best to lie on a chair or blanket. You can use some apps to help locate Perseus. You don't have to focus on Perseus. Meteors may appear anywhere in the night sky. Maintaining a wide field of vision is key. Be patient and you can see up to 100 meteors per hour. You may even see a stunning fireball!

SLR camera shooting tips : SLR cameras need to be equipped with wide-angle lenses or large aperture fixed focus lenses, and a stable tripod. Set the camera's aperture to maximum light, long exposure time of 15-30 seconds, and high sensitivity (ISO800-3200) is required. And set the manual focus to infinity, use the interval shooting function or remote control to shoot continuously, and choose interesting foregrounds such as trees or mountains. Noise reduction, stack synthesis and color adjustment after shooting will capture more beautiful meteor moments.

Summarize

The Perseid meteor shower is one of the most popular astronomical phenomena every year. Its abundant number of meteors, gorgeous color changes and unique observation experience make it a highlight in the summer night sky. I believe that everyone not only has a deeper understanding of meteor showers, but also has mastered the skills of how to better observe and photograph meteor showers. I hope that every stargazer can spend a night full of miracles and romance with the Perseid meteor shower. Let us look forward to it together, look up at the starry sky, and encounter the meteor that changes color gradually!

References:

1.Zhilyaev, Boris Ephimovich, et al. "Methods for estimating some characteristics of meteoroids in the wake of intrusions." 22 International scientific conference Astronomical School of Young Scientists. December 11–12 2020, p. 20-22 2020.