Since radio WAVES travel at or near the speed of light in space they have traveled the same number of years from broadcast date to the current date, In Example IE: Radio transmitted in 1920 would have gone 90 light years by 2010. How ever there seems to be some question as to how far those waves can travel prior to loss of the ability to detect them. SETI (I THINK) believes that the newest array they have could detect our oldest radio from the 1920s up to or about 50 to 100 light years away. The more sophisticated and sensitive the equipment the weaker the signal you can detect. A radio WAVE is like an expanding ball getting weaker for many reasons as it travels through space. Some signal is "reflected" to other directions from some material, and some material will absorb the waves. However, even a degraded signal that could not be received as a sound radio channel would still give a "SINGLE Freq. Noise" for many more light years. In nature "Single Freq. Noise" does not happen, As far as we know currently. So even if we were or ET was to receive a radio signal that was just "Noise" but on a single frequency, that would mean most likely an advanced or at least tech society had created it.
In simple terms, here is how to do the math:
light travels around 5.879Trillion Miles in a year. (1LY[lightyear])
multiply that by 90, you get 529.1Trillion miles. so our first transmission are roughly that distance away from earth.
now, that might seem extremely far... but it really isn't in terms of ET, based on the distance of stars, that only passes a few stars, and who says every star gets life.
But as the question asks specifically 'how many' then answering 'a few' is not very illuminating, the following may be the best estimate.
As a function of distance, the Gliese star catalog lists the following number of stars. A parsec is 3.26 light years.Distance Number DensityDistance from Sun in parsecsnumber of starsstars/cubic parsec5630.120103280.0781510080.0712021270.0632534960.053http://www.stellarium.com/nearstar/nearby.html
So as our first radio transmissions are now (2011) approaching 90 years old it may be that we have broadcast to 4000 plus stars.
Radio waves are predominantly used for communication in space due to their long wavelengths that enable them to travel long distances without much interference. These waves are able to penetrate Earth's atmosphere and travel through space to reach distant spacecraft and satellites.
Scientists use radio telescopes to detect and study radio waves traveling through space. These telescopes can collect and analyze radio signals from various celestial objects like stars, galaxies, and pulsars. By studying these radio waves, scientists can gain insights into the properties and behavior of objects in the universe.
Signals travel in space using electromagnetic waves, such as radio waves or light. These waves can travel through vacuum without a medium and carry information encoded in their frequency, amplitude, or phase. Communication between spacecraft and Earth, for example, is achieved by transmitting signals through space using antennas and receivers.
light and radio waves are energy themselves, so they are not dependent on "something" being there to travel through as sound is. the reason that sound cannot pass through a vacuum is because it is a set of energy waves that flow through the molecules of the substance. causing the first molecule to bump into the second, second into the third, third to the fourth and so on.
Objects such as pulsars, radio galaxies, supernova remnants, and active galactic nuclei are known to emit radio waves in space. These emissions can be detected by radio telescopes and provide valuable information about the nature and behavior of these cosmic objects.
Radio waves were detected in space for the first time in 1938. At the time, radio waves traveled around 60 light years away.
Karl G. Janky
radio astronomy...:)
radio astronomy
radio astronomy
radio astronomy
october 2 1608
A radio telescope.
Radio waves are often referred to as space waves because they have the ability to move through space. Radio waves are a type of electromagnetic radiation.
radio waves
Radio Waves! (:
radio waves