An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



Number of Results: 10 Search : digit
accurate to n significant digits
  رشمند با n رقم ِ نشانار   
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.

analog-to-digital converter
  هاگردگر ِ آناگویه-رقمی   
hâgardgar-e ânâguyé-raqami

Fr.: convertisseur analogique-numérique   

In electronics, a device that converts the analog signal to → analog-to-digital units or counts.

analogue; → digital; → converter.

analog-to-digital unit (ADU)
  یکای ِ آناگویه-رقمی   
yekâ-ye ânâguyé-raqami

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).

analogue; → digital; → unit.

binary digit (bit)
  رقم ِ درین، ~ دودو‌یی، بیت   
raqam-e dorin, ~ dodoi, bit

Fr.: chiffre binaire   

Either of the digits 0 or 1, used in the → binary number system.

binary, → digit.

raqam (#)

Fr.: chiffre   

A symbol, numeral, or graphic character that represents an integer.

From L. digitus "finger, toe."

Raqam, from Ar.

raqami (#)

Fr.: numérique   

1) Of or pertaining to a digit.
2) Representing data as a series of numerical values. Often opposed to → analogue.

digit + → -al.

digital computer
  رایانگر ِ رقمی   
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.

digital + → computer.

raqamidan (#)

Fr.: numériser   

To convert an → analogue signal to a → digital signal that represents the same information as the analogue signal.

digit + → -ize.

significant digit
  رقم ِ نشانار   
raqam-e nešânâr

Fr.: chiffre significatif   

The number of digits used to express a measured or calculated quantity. Rules for deciding the number of significant digits:
The leftmost digit which is not a zero is the most significant digit.
If the number does not have a decimal point, the rightmost digit which is not a zero is the least significant digit.
If the number does have a decimal point, the rightmost significant digit is the least significant digit, even if it's a zero.
Every digit between the least and most significant digits should be counted as a significant digit.

significant; → digit.

Sloan Digital Sky Survey (SDSS)
  بردید ِ عددی ِ آسمان ِ Sloan   
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-Chretienaltitude-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.