Light Years Traveled By Radio And Tv Signals

The radio and television signals we have been broadcasting for over a century have travelled a distance of about 200 light-years from Earth. This means that any alien civilisations that have picked up our signals must be within a bubble of 200 light-years from us. Our signals have reached 75 star systems that can see us, and astronomers have already observed exoplanets orbiting four of them. However, the vastness of space means that our radio and TV signals are so weak by the time they reach 100 light-years away that they are practically undetectable.

The first radio transmission was made in 1895

Marconi's first successful demonstration involved sending a wireless Morse Code message to a source over a kilometre away. This was a significant development, as it showed that electromagnetic radio waves could be transmitted through free space and detected over a short distance.

Marconi's early work in radio transmission was not without competition. Other inventors, such as Nikola Tesla, were also working on similar devices. However, Marconi was able to gain financial backing and positive publicity, which helped him become known as the "inventor" of radio.

In the years that followed, Marconi continued to refine his technology, transmitting messages across longer distances. In 1901, he successfully sent a radio transmission across the Atlantic Ocean, from Cornwall, England, to Newfoundland, Canada—a distance of over 2,000 miles. This achievement brought him worldwide fame and further established the potential of radio as a communication tool.

Today, radio waves have travelled far beyond our planet, extending more than 200 light-years into space. While this may seem like a vast distance, it is a small fraction of the size of our galaxy, the Milky Way, which stretches between 100,000 and 180,000 light-years across.

Considering the immense scale of our galaxy, the search for extraterrestrial intelligence (SETI) faces significant challenges. Even assuming advanced alien civilizations possess the necessary technological capabilities, the probability of their proximity within our radio wave bubble is extremely low.

Signals have travelled 303 trillion km, past the nearest star

Since the development of radio and television stations, we have been broadcasting radio waves in all directions. These signals have travelled about 303 trillion kilometres, well past the nearest star.

To calculate this distance, we need to know that radio waves travel at the speed of light, which is 300,000 km/sec. We then multiply this by the number of seconds in a year (31,536,000) and then by the number of years we've been broadcasting for. If we've been broadcasting for 32 years, for example, the calculation would be: 300,000 x 31,536,000 x 32 = 303,229,440,000,000,000 km (or 303 trillion km).

Using light years (the distance that light travels in a year) can simplify this calculation. If we've been broadcasting for 32 years, then our radio signals could be detected at a distance of over 32 light years, which is plenty of distance to be past the nearest star. Proxima Centauri, for example, is only 4.25 light years away (about 40 trillion km).

Our radio signals have now reached 75 star systems that can also see Earth. This was calculated by Lisa Kaltenegger at Cornell University in Ithaca and Jackie Faherty at the American Museum of Natural History in New York City. They used the Gaia Catalogue, a new 3D map of our galaxy showing the distance and motion of more than 100 million stars, to determine the size of the sphere that our radio signals have covered and the stars that sit inside it.

Despite reaching 75 star systems, our radio signals have not even come close to reaching the centre of our galaxy, which is 30,000 light years away. It will take another 29,968 years for our radio signals to reach the centre of the Milky Way.

Aliens within 200 light-years could have heard us

Since the development of radio and television stations, we have been broadcasting radio waves in all directions. Radio signals, being a form of electromagnetic radiation, travel at the speed of light. In the 126 years since we began emitting these signals, our radio bubble has expanded to a diameter of 200 light-years. This means that any alien civilizations within this bubble could have heard us.

The Milky Way, our galaxy, stretches between 100,000 and 180,000 light-years across. This means that a signal broadcast from one side of the galaxy would take 100,000 years or more to reach the other side. In contrast, our radio bubble, at 200 light-years in diameter, is minuscule in comparison.

The radio signals we emit are incredibly faint, and for aliens to detect them, they would need sensitive radio telescopes. Even if a civilization 100 light-years away had the technology to detect our earliest radio waves, we would still have to wait until the 22nd century for a response, assuming they sent one immediately upon receiving our signal.

The Search for Extraterrestrial Intelligence (SETI) Institute is constantly listening for potential alien radio signals with advanced radio telescopes, but given the vast size of the galaxy, the odds of making contact with another intelligent species are incredibly slim. The galaxy contains an estimated 100 to 400 billion stars, and even if we sent 100 messages at random, it is highly unlikely that any would reach an alien civilization.

While we may have been heard by aliens within 200 light-years, the chances of receiving a response anytime soon are remote. The vast distances and technological limitations make the search for extraterrestrial intelligence a challenging endeavor.

The first intentional transmission to space was in 1974

Radio waves have been broadcast into space since the invention of radio and television stations. Signals have travelled about 303 trillion kilometres, which is well past the nearest star, Proxima Centauri, which is only 4.25 light years away. However, our broadcasts have not even come close to reaching the centre of our galaxy, which is 30,000 light years away.

The Arecibo message was sent in the direction of M13, a globular star cluster orbiting the centre of our Milky Way galaxy. M13 is about 25,000 light-years from Earth. The message will reach M13 in about 25,000 years, and it will take at least another 25,000 years for any potential reply to reach Earth.

The Arecibo Observatory collapsed in 2020 when its 900-ton receiver platform came loose from its cables and fell onto the reflector dish.

75 star systems that can see us are within a 100 light-year sphere

Since the development of radio and television stations, we have been broadcasting radio waves in all directions. These radio signals have now reached 75 star systems that can also see Earth. This was calculated by astronomers Lisa Kaltenegger and Jackie Faherty, who used the Gaia Catalogue, a new 3D map of our galaxy showing the distance and motion of over 100 million stars. The data for the map comes from the European Space Agency's Gaia spacecraft, which was launched in 2013 and is mapping the position and motion of about 1 billion astronomical objects.

The first long-distance radio broadcasts were made by Guglielmo Marconi in 1895, with his assistant tuning in from less than a kilometre away. By the time of his death in 1937, radio signals were routinely used to communicate across the world. These signals have also travelled into space, signalling that humanity has emerged as a technologically advanced species.

The 75 star systems that can see us are within a 100-light-year sphere. This includes the Ross128 star system, which is the 13th closest to the Sun and the second closest with a transiting Earth-size exoplanet. There is also Teegarden's Star, with at least two Earth-mass exoplanets, and the Trappist-1 star system with seven Earth-sized planets, four of which are in the habitable zone.

Our radio signals will continue to radiate outwards, and Kaltenegger and Faherty have identified star systems that will receive our signals in the next 200 years or so and will also be able to see us. They estimate that there are 1,715 stars within 326 light-years that have been able to spot life on a transiting Earth since early human civilization, with an additional 319 stars entering this vantage point in the next 5,000 years.

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