Glossary – S


in computer science, sandbox means to isolate a computer program such that it is unable to affect any other part of the computer, software or hardware.
a natural or man-made object that orbits a planet or other object.
Scientific Method
a general systematic procedure for learning about the world. It consists of gathering information (data), and testing ideas through experiments and careful observations.
when high energy light, such as gamma rays, strikes certain substances, such as sodium iodide crystals, it produces a flash of lower energy light. Physicists call this process scintillation.
Seeing Disk
the apparent size of a point source like a star that is smeared out due to atmospheric blurring.
in optics, the resolution and range of a detector.
Seyfert Galaxy
a spiral galaxy (named for astronomer Carl Seyfert) with an extremely bright nucleus that emits strong emission lines. In Type I Seyferts the inner disk is tipped to our line-of-sight, allowing us to see broad emission lines produced in regions where the gas moves very fast, 1000 km/s or more. In Type II Seyferts the angle is such that we do not see down to these fast-moving regions, so we see only relatively narrow emission lines, about 200 km/s in width.
Short Gamma-Ray Burst
A gamma-ray burst which typically lasts less than about 2 seconds and which is usually associated with the merger of a pair of neutron stars or black holes (or one of each).
Sieverts (unit)
the biologically effective radiation dose from the absorption of one joule of radiation energy by one kilogram of matter.
in this context, singularity is a place in space where mass density and gravitational force become infinite.
Sodium Iodide Crystals
these specially treated crystals, made from sodium and iodine atoms, are used as part of gamma-ray detectors. The gamma rays produce flashes of optical light when they pass through the crystals, and the optical flashes are detected by photomultipliers – devices that convert visible light into electric current.
Soft Gamma Repeater
A gamma-ray burst which typically peaks in less energetic (“softer”) regions of the gamma-ray spectrum and which is associated with disruptions on the surfaces of magnetars brought about by sudden shifts in their powerful magnetic fields.
Soft X-ray
The lowest energy X-rays are commonly referred to as “soft” X-rays; the energy of these X-rays is typically in the range 0.1 to 10 keV.
this is one of the proper names for the Sun. Sol was the god of the sun in Roman mythology. It is from this root that words like “Solar” are derived.
Solar Mass
a unit of mass where the mass of the Sun is 1. Generally used for the mass of stars and galaxies. One solar mass is 2 x 1030 kg.
Solar System
a collection of planets, moons, comets, etc. which orbits a star. Our solar system is roughly 1010 kilometers (1013 meters) across.
Solar Wind
the term given to the stream of charged particles that are ejected from the Sun’s atmosphere. One of the effects of the interaction of solar wind and the Earth’s atmosphere is a creation of beautiful light patterns in sky known as auroras.
Source Code
the set of computer instructions that makes up computer programs.
Space Station
an artificial satellite orbiting a star, planet, or moon that is capable of supporting one or more crew members.
the three physical dimensions (length, width, and height), plus the dimension of time is spacetime. An object moving around in a volume over a period of time is moving through spacetime.
an instrument that measures the intensity of light over a given range of wavelengths. In astronomy, spectrometers are especially useful in determining what elements make up a given source of electromagnetic energy. A prism is a very simple type of optical spectrometer.
the scientific technique in which the intensity of light at different colors or wavelengths is measured. Comparing the measurements at different wavelengths can help to determine which elements are present in the light source.
the distribution of flux (energy or photons) with energy. Basically, the spectrum of an object is a histogram of the total energy it emits at each photon energy, or if the photon flux is being measured, then the spectrum could be the number of photons emitted at each photon energy.
Spiral Galaxy
these galaxies are flattened disks with long spiraling arms that extend out from a central core or bulge. In the arms are large amounts of interstellar matter which lead to high rates of new star formation.
Stellar Black Hole
a black hole formed from collapse of a dying star with a mass at least ten times that of our Sun. Scientists have observed more than a dozen stellar black holes in our Milky Way galaxy, and have also detected them in other galaxies that are nearby.
Stellar Classification
this is a system in which stars are given a classification of O, B, A, F, G, A, K, or M based on their surface temperature, with O being the hottest and M being the coolest. Our Sun is a type G, with a surface temperature of about 6000K. Officially, this is known as the Morgan-Keenan spectral classification system.
Stellar Density
the number of stars that exist within a given region of space.
Stellar Flare
an explosion in the atmosphere of a star caused by a sudden release of magnetic energy. When this occurs in our own sun we call it a Solar Flare.
Stellar (star) Formation
the process by which stars are formed.
Stellar Nurseries
giant molecular clouds in interstellar space where the abundance of hydrogen molecules (H2) is such that parts of the clouds collapse under their own gravity to form new stars.
Strong and Weak Nuclear Force
the strong and weak nuclear forces are short-range forces that act only inside atomic nuclei. The strong force holds the nuclei together. The weak force is responsible for radioactivity and the emission of particles from nuclei.
Supermassive Black Hole
a black hole with mass on the order of millions or billions of solar masses. There is scientific evidence for a 4-million solar mass supermassive black hole at the center of our Milky Way galaxy, as well as much larger black holes at the cores of distant galaxies.
Supergiant (star)
the most massive type of star. A supergiant may have a mass between 10 and 70 times that of the Sun, or even more. Its size (diameter) will typically be several times larger than that of our own Sun.
Supernova (pl. supernovae)
the titanic explosion of a massive star at the end of its life. The outer layers explode outward, creating a supernova remnant, while the inner core collapses to become a neutron star or black hole.
Supernova Remnant (SNR)
the expanding gas left over from a supernova.
Surface Area
a 2-dimensional measurement that has both a length and a width. For instance, it could be the area on top of a table, in which case the surface area would be the product of the table’s length and width. Surface area can also be the total area covering a shape. As an example, the surface area of a cube is the length of one of its sides squared (that’s the area of a face of the cube) times 6 (since a cube has 6 faces).
in astronomy, a survey is a map that spans some region of the sky; some surveys even show the entire observable universe. Surveys can be taken in many different wavelengths, producing very different images of the Universe.
a first-of-its-kind multi-wavelength satellite, launched in 2004, dedicated to the study of gamma-ray burst (GRB) science. Its three instruments work together to observe GRBs and afterglows in the gamma ray, X-ray, ultraviolet, and optical wavebands.
a near-Earth comet independently discovered in 1862 by American astronomers and comet hunters Lewis Swift and Horace Tuttle. It is the source of the Perseid meteors.
Synchrotron Radiation
radiation produced when charged particles accelerate in a curved path around magnetic field line.