Earth's Radio Sphere
Earth's Radio Sphere
Goals: Understand the relationship between light-travel time and distance in the Universe; see the extent of Earth's radio signals in the Galaxy.
Before starting, turn on: stars, mwVis, expl
You will be using: radec, 1kly
With the stars and exoplanets on, let's turn on a marker of where Earth's earliest radio transmissions are in interstellar space. Turn on the celestial coordinates. From this perspective, this group no longer acts like a coordinate system but rather doubles as Earth's radio sphere.
The radio sphere shows the boundary of Earth's radio signals beginning in the late 1930s and into the early 1940s, when radar, television carrier waves, and atomic testing started sending strong radio signals into space. Strong enough to pass through Earth's ionosphere, these signals travel into interstellar space at the speed of light. A signal that left in 1940 is, as of 2007, 67 light-years away. The radio sphere then contains a history of Earth's signals and implies what you likely know: looking out into space means you're looking back in time. At 52 light-years away (as of 2007), we would detect an original broadcast of The Honeymooners, and at 43 light-years the Beatles appear on Ed Sullivan.
With the radio sphere and the exoplanets on, it is now possible to see how many planetary systems have heard from us. How many do you count?
Fly away from the radio sphere so that you see most of the stars. The radio sphere is the farthest extent of mankind's presence in our Galaxy and the Universe, just 66 light-years from Earth. Turn on the 1,000-light-year grid and you begin to see just how small an influence we've had in the Galaxy. In the coming tutorials, we'll explore how much larger the Galaxy is, but let's start with the stars.
© 2002-2005 American Museum of Natural History
Last Modified: 2007-12-19 by Brian Abbott