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Draconids
The Draconids, historically called the Giacobinids, are an annual meteor shower from comet 21P/Giacobini-Zinner, peaking around October 8 and best viewed in the evening from Draco.
Draft (hull)
A ship's draft (draught) is the vertical distance from the waterline to the bottom of the hull, read from numbered scales painted at the bow and stern.
Drafting (aerodynamics)
Drafting, also called slipstreaming, is positioning a vehicle, cyclist, or runner close behind another to reduce aerodynamic drag; a trailing cyclist can cut drag by 15–50%.
Drag (physics)
Drag, also known as air resistance or drag force, is a mechanical force that opposes an object's motion through a fluid such as air or water.
Drag coefficient
The drag coefficient, or coefficient of drag, is a dimensionless number summarizing the effects of shape, inclination, and flow conditions on aerodynamic drag, used in the drag equation.
Drag equation
The drag equation is an aerodynamics formula giving the drag force on a body moving through a fluid, as a product of drag coefficient, density, velocity squared, and area.
Dragon (龙) (zodiac)
The Dragon (龙) is the fifth sign of the twelve-year Chinese zodiac, paired with the earthly branch Chen, and the only mythical creature among the twelve animals.
Dragon Bravo Fire
Dragon Bravo Fire was a 2025 lightning-caused wildfire in Grand Canyon National Park. It burned for nearly three months, destroying the Grand Canyon Lodge, and killed one firefighter.
Drainage density
Drainage density is a measure of how finely a landscape is dissected by stream channels: the total stream length in a drainage basin divided by its area, first formalized by Robert E. Horton in 1932.
Drake equation
The Drake equation, also called the Green Bank equation, is a 1961 formula by Frank Drake estimating the number of radio-transmitting civilizations in the Milky Way.
Dram (unit)
The dram (drachm, abbreviated dr) is a small traditional weight unit, 1/16 ounce in the avoirdupois system, and, as the fluid dram, a volume of 1/8 fluid ounce.
DRASTIC
DRASTIC is a GIS-based overlay index method that rates seven hydrogeologic factors, named in its acronym, to assess groundwater vulnerability to contamination from surface pollutants.
Dravite
Dravite is a magnesium-rich member of the tourmaline group of minerals, named in the 1880s for the Drava river near its type locality in Slovenia.
Drazin inverse
The Drazin inverse is a unique pseudoinverse of a square matrix that inverts its invertible part and annihilates its nilpotent part, introduced by M. P. Drazin in 1958.
Dredge-up
Dredge-up is a set of mixing episodes in low- and intermediate-mass stars where the convective envelope carries nuclear-burning products like carbon and s-process elements to the surface.
Drell–Yan process
The Drell–Yan process is a particle physics effect in which a quark and antiquark from colliding hadrons annihilate to produce a lepton pair, proposed by Sid Drell and Tung-Mow Yan.
Dressed state
A dressed state is an eigenstate of the combined atom and light field system, not of the free atom alone, underlying laser cooling and resonance fluorescence.
Drew Shindell
Drew Shindell, also published as D. T. Shindell, is an American atmospheric scientist at Duke University who spent 1997 to 2014 at NASA and studies methane and climate policy.
Drift (stream ecology)
Drift in stream ecology is the downstream transport of benthic invertebrates in the water column, a primary food source for stream fishes and a means of dispersal.
Drift chamber
A drift chamber is a gaseous particle detector that measures charged-particle trajectories by timing ionization electrons drifting to sense wires, reconstructing tracks and momentum in a magnetic field.
Drift velocity
Drift velocity is the average velocity a charge carrier acquires in a material under an applied electric field, typically less than a millimeter per second in metals.
Drift wave
A drift wave is a low-frequency electrostatic fluctuation of a magnetized plasma driven by a pressure gradient; its turbulence causes the dominant cross-field transport in tokamaks and stellarators.
Drift waves and microinstabilities
Drift waves and microinstabilities, also known as the drift wave instability, are low-frequency plasma oscillations driven by density and temperature gradients, and they set the practical limit on tokamak confinement through turbulent transport.
Drift-wave turbulence
Drift-wave turbulence is the turbulent state of a magnetized plasma in which drift waves, driven unstable by density and temperature gradients, transport particles, energy, and momentum across magnetic field lines.
Drifter (oceanography)
A drifter, also known as a Lagrangian drifter, is a satellite-tracked ocean buoy with a subsurface drogue at 15 m depth that follows currents while measuring temperature and position.
Drill bit
A drill bit is a rotating cutting tool with cutting edges and helical flutes that remove chips, made in materials from carbon steel to cemented carbide.
Drill bit sizes
Drill bit sizes designate a twist drill's cutting diameter in four coexisting systems: fractional inch, number gauge, letter gauge, and metric, so a stock drill sits near almost any needed hole size.
Drill hole surveying and downhole orientation
Drill hole surveying and downhole orientation measure a borehole's inclination and azimuth with depth to reconstruct its three-dimensional path, and determine the in-hole direction of core features.
Drinfeld center
The Drinfeld center of a monoidal category is a braided monoidal category whose objects are pairs with half-braidings, the categorical counterpart of Drinfeld's quantum double of a Hopf algebra.
Drinfeld double
The Drinfeld double, also called the quantum double, is a Hopf algebra built from a Hopf algebra and its dual, introduced by Vladimir Drinfeld in 1986.