accurate to n significant digits
rašmand bâ n raqam-e nešânâr
Fr.: écrit avec n chiffres significatifs
An expression specifying the number of meaningful digits used to express the value of a measured quantity. Same as accurate to n significant figures. For example, e = 2.71828 ... = 2.718 is rounded to four significant digits, and 2.72 to three significant digits. → accurate to n decimal places.
→ accurate; → significant; → digit.
Fr.: convertisseur analogique-numérique
In electronics, a device that converts the analog signal to → analog-to-digital units or counts.
analog-to-digital unit (ADU)
Fr.: unité analogue-numérique
A number that represents a → charge-coupled device (CCD)'s output and is proportional to the → electron charge created by the → photons, plus the constant → bias offset. The relationship between the ADUs generated and the number of electrons acquired on the CCD is defined by the → CCD gain. Intensities given in ADUs provide a convenient method for comparing images and data generated by different cameras. Also referred to as → count and digital number. In most cases, the analog signal is digitalized by an analog-to-digital (A/D) converter and fed into a computer where further manipulation and analysis are done on what the detector originally produced from the star's photons (Howell, S.B., Handbook of CCD Astronomy, Cambridge Univ. Press, 2000).
binary digit (bit)
raqam-e dorin, ~ dodoi, bit
Fr.: chiffre binaire
Either of the digits 0 or 1, used in the → binary number system.
A symbol, numeral, or graphic character that represents an integer.
From L. digitus "finger, toe."
Raqam, from Ar.
1) Of or pertaining to a digit.
râyângar-e raqami (#)
Fr.: ordinateur numérique
A computer that accepts and operates with → discrete data in the form of combinations of digits, letters, or other characters. In modern terminology, generally called computer.
To convert an → analogue signal to a → digital signal that represents the same information as the analogue signal.
Fr.: chiffre significatif
The number of digits used to express a measured or calculated quantity.
Rules for deciding the number of significant digits:
→ significant; → digit.
Sloan Digital Sky Survey (SDSS)
bardid-e adadi-ye âsmân-e Sloan
Fr.: relevé numérique du ciel Sloan
A major → redshift survey using a dedicated 2.5-m wide angle telescope with different modes in → imaging and → spectroscopy. The telescope, a modified → Ritchey-Chretien→ altitude-azimuth type is located at Apache Point Observatory, south east New Mexico, United States. A large consortium of universities and institutions all over the world participate in the project. The telescope started its observations in 2000, taking spectra and images of about 35% of the night sky, with 3 million spectra and 500 million images coming together to form the most comprehensive astrophysical catalog in the world. This catalog contains millions of galaxies up to z = 1, bright → quasars up to z = 6, with images in five major filter bands (u, g, r, i and z). SDSS was divided into multiple surveys/projects: SDSS I (2000-2005); SDSS II (2005-2008), including the Sloan Supernova Survey; SDSS III (2008-2014), including the APO Galactic Evolution Experiment (APOGEE), Baryon Oscillation Spectroscopic Survey (BOSS); SDSS IV (2014-2020), including the Mapping Nearby Galaxies at APO (MaNGA).
Named after the Alfred P. Sloan Foundation, which contributed significant funding; → digital; → sky; → survey.