The size of the Universe is immense. Traditional units of measurement (such as meters and kilometers) are of little use as far as astronomy is concerned.
The basic astronomical unit of distance, known as the AU (which stands for Astronomical Unit) is the size of the large semi-axis of the Earth's orbit, which is equal to 149 million kilometers. Larger units of distance, such as light-years and parsecs - as well as their derivatives (kiloparsecs and megaparsecs) - are employed in stellar astronomy and cosmology.
One light-year is the distance that is passed by a ray of light in a vacuum during one Earth year. It is approximately equal to 9.5∙1015 m.
A parsec refers to the distance at which one astronomical unit subtends one second of arc. One parsec is equal to 3.0857∙1016 meters or 3.2616 light years, which is also equal to 206,265 astronomical units, or 3.086∙1016 m.
This model will enable you to compare the characteristic sizes and distances in our Universe. The slides in the model's center-box display both astronomic and terrestrial objects (the Kremlin, a neutron star, the Earth, the Solar System, the galaxy), as well as their characteristic sizes. Use the slider bar at the bottom of the model to access the next slide.
Press "Run" button to activate the model. The slides will change at a 3-second interval, starting with current one. Press "Stop" to suspend the model. Press "Reset" to return to the model's initial state.