How Fast Do Radio Waves Travel in Space? & How Far?


Written by

Rafeal Hart


Fact-checked by

Norris Howe

how fast do radio waves travel in space

Radio waves travel very fast. In space, these radio waves would travel at the speed of light– around 3 x 108 m/s. These radio signals could reach the moon in a matter of seconds!

However, these radio waves pass through different mediums when they travel. So, when these waves pass through an object, their speed also changes. Some factors include the object’s absorption rate and conductivity.

How fast do radio waves travel in space? Read more to find out.

What Are Radio Waves?


Radio waves are electromagnetic radiations that convert mechanical vibrations into sound waves. It’s the basic building block of radio communication.

They are measured in wavelengths, the distance a radio wave travels per cycle. Its wavelengths range from 1 mm to more than 100 km. Also, the number of cycles is called frequencies, represented in Hertz (Hz).

Types of Radio Wave Propagation

Radio waves can be divided into different bands. These include:


  • Low to medium frequency

These frequencies are the first kind of radio waves that have been discovered. The radio signals travel at a frequency of less than 1MHz. This includes ELF (extremely low frequency), and VLF (very low frequency) ranges, from below 3 to around 30 kHz.

However, because these frequencies have a relatively long range, they are perfect for undersea communications.

  • Short-wave frequency

This frequency range in radio waves has a wavelength of 1.7 – 29.8 mHz. It’s also classified as high-frequency radio that can broadcast within thousands of kilometers.

  • Higher frequency

Higher frequencies include HF (high frequency), VHF (very high frequency), and UHF (ultrahigh frequency), ranging from 10 MHz to 1 GHz.

This type of frequency is mostly used in FM, GPS, broadcast audio, cell phones, and/or public service radios.

  • Highest frequency

The highest radio wave frequencies range from 10 GHz to 100 GHz. These include the SHF (super-high frequency) and EHF (extremely high frequency), which are mostly used in Wi-Fi, Bluetooth, and wireless USBs. These are also used for radars.

The Speed of Radio Waves in Space


If you’re wondering at what speed do radio waves travel, the radio waves’ speed follows the speed of light.

In a vacuum, the speed of light (and radio waves) is 299,792,458 meters per second. That’s an estimated 300,000,000 meters per second.

In km, that’s roughly 300,000 kilometers per second. In mph, that’s 670,616,279 miles per hour.

On Earth, the speed of radio waves is fast because of the short distance. But compared to Earth, the speed of radio waves in space might seem slow.

That’s because radio waves travel through space in billions of kilometers. For radio waves to reach Pluto, it’d take 4.5 hours before you can send a message.

Note that radio waves aren’t sound waves or travel at the speed of sound. Sound waves travel at a speed of only 331.29 meters per second, compared to light (radio waves) which travels 300,000,000 meters per second.

Other Types of Electromagnetic Radiation


Aside from radio waves with the longest wavelengths compared to other types of electromagnetic waves, there are more types. These are classified depending on their frequencies. These are the types of radiation in the electromagnetic spectrum– from the longest to the shortest.

  • Radio Waves (103) used for TV and radio broadcasting
  • Microwaves (10-2) are used for cooking and signals for phones, radars, etc.
  • Infrared (10-5) is used for transmitting heat from radiators and the sun
  • Visible Light (10-6) is used to see the things that are visible to us today
  • Ultraviolet (10-8) used for fluorescence
  • X-ray (10-11) is used to see what’s inside an object
  • Gamma Ray (10-12) is used for medical purposes, such as to kill cancer cells

Factors Affecting Radio Wave Speed in Space


Multiple factors can affect the radio waves’ speed in space. Some of these include:

  • Obstacles in the path the radio waves are taking
  • Antenna distance
  • Earth’s curvature
  • Receiving and transmitting antenna height

How Are Radio Waves Used in Space?


Radio waves are used (in space) for spacecraft communication. Each spacecraft usually has a radio wave transmitter and receiver. They also have a method of interpreting and working on the data received.

Radio waves can also be used in radio telescopes for astronomy– to see galaxies, planets, comets, stars, and other objects in space.

Frequently Asked Questions


What is the difference between radio waves on Earth and in space?

Radio waves on Earth are typically the same as radio waves in space. Both of them travel at the speed of light. But how far it goes in space makes it seem like radio waves in space are slower.

On Earth, radio waves are mostly used to tune in to your radio. In space, they’re used for spacecraft communication.

How do radio telescopes help in space exploration?

Radio telescopes let you view planets, stars, and other extraterrestrial bodies in space. People can also learn about these objects’ structure, composition, and motion.

What are the challenges of using radio waves for space communication?

There are many challenges when using radio waves for space communication. There may be other background radio signals that might interfere with such. These noise interferences are called SNR (signal-to-noise ratio). The radio signal may go static when there’s natural and human-made interference.

How long does it take for a radio message to travel from Earth to the moon?

A radio message coming from Earth takes only a few seconds to reach the moon. It takes 2.5 seconds– to be exact.


So, how fast do radio waves travel in space? On average, they travel at the speed of light– 300,000,000 m/s. But, many factors could slow these radio waves down. So, space communication could be very challenging.

Sending a radio message to the moon takes only a few seconds. But the communication delay with a spacecraft traveling to farther places like Pluto and beyond is far more stressful.

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