Here Navigation There Navigation Everywhere Navigation

Topics: the shape of speed.

More about Bow shocks

large bow shocks triptych

As a duck paddles across a pond, it creates ripples or waves that move out in front of it. If the duck paddles fast enough, the ripples will merge into a V-shaped wall of water called a bow wave. Bow waves are familiar sights in front of boats as well, and can also be formed

in the atmosphere and in space when objects move more rapidly than the speed of waves in their liquid or gas environments. These waves are usually called bow waves when they are produced in water, and bow shocks, or shock waves, in gases.

More Info.


Image: Patrick J. Bray

Bow waves in water create drag force that slows down the object, and in the case of large ships, can pose a risk to smaller boats, especially in a harbor. Streamlined shapes, mimicking those found in nature, are designed to produce as small a bow wave as possible.

An object moving through the air, or the rarified gas in the solar system, a galaxy or intergalactic space, of space, creates a series of pressure waves, or sound waves. When the object travels at the speed equal to or greater than the speed of sound in the gas, these waves merge into a 3-dimensional bow shock, or shock cone. The width of the bow wave or shock cone depends on the speed of the object. The faster the object travels, the narrower the cone becomes.

More about Bow waves

A nice applet illustrating the formation of bow waves, a.k.a. bow shocks can be found at:

Dolphins riding the wave of a ship


Fun Facts about Bow Shocks
More on supersonic shocks

The Mach number M of an object moving at a speed V through a gas with a sound speed Vs is defined as M = V/Vs. A shock wave is formed when M = 1, sometimes referred to as Mach 1, motion with M > 1 is called supersonic motion. For air at sea level at 20 degrees C, an object reaches Mach 1 at 1,225 km/hr (761 mph, or 1,116 feet/s). The shock wave forms a cone, with an opening angle A determined by the Mach number (sin A = 1/M) with higher Mach numbers producing cones with smaller opening angles.

Bullet Shock Wave

Image: Harold E. Edgerton, Smithsonian American Art Museum

Fun Facts about Supersonic Shocks
More on cosmic bow shocks

With so many objects out there moving so fast, it is not surprising that bow shocks are common in the cosmos. In general, cosmic bow shocks can be difficult to detect because they are relatively thin, and are usually found in an environment where a lot is happening. In spite of this, astronomers have used the Chandra, Hubble and Spitzer telescopes to collect some spectacular examples of bow shocks. The bow shocks are like weather vanes: they can reveal which way the wind is blowing. They can also tell how strong the wind is.

Bullet Shock Wave

Image: X-ray: NASA/CXC/CfA/M.Markevitch et al.; Optical: NASA/STScI; Magellan/U.Arizona/D.Clowe et al.; Lensing Map: NASA/STScI; ESO WFI; Magellan/U.Arizona/D.Clowe et al.

Fun Facts about Cosmic Bow Shocks

Back to Bow shocks page

"Here, There, & Everywhere" (HTE) is supported by the National Aeronautics and Space Administration under grant NNX11AH28G issued through the Science Mission Directorate.

HTE was developed by the Chandra X-ray Center, at the Smithsonian Astrophysical Observatory, in Cambridge, MA.

Email:   |   Phone: 617.496.7941
Follow us: #HTEScience on Twitter