Astrophysics (index)about


(z, redshift parameter)
(change to longer wavelengths due to Doppler affects)

Redshift is a lengthening of wavelengths, e.g., of spectral lines, due to Doppler effects of radial motion of the radiation source away from the observer (i.e., its recessional velocity). Given the expansion of the universe, redshift is used as a measure of distance and time, and a redshift due to this is called a cosmological redshift.

Smaller redshifts and blue shifts (for the analogous shortening of the wavelength from sources moving toward the observer) are also measured to determine radial velocity in studies of peculiar velocity and of objects orbiting stars such as extra-solar planets and binary star companions. Measurements using specially developed spectrographs can determine radial velocities and radial velocity differences as small as 1 meter per second.

The redshift parameter (often just called redshift) z is:

     observed wavelength - rest wavelength
z =  —————————————————————————————————————
              rest wavelength

The relationship between z and the recessional velocity is:

              1 + v/c
1 + z = sqrt( ——————— )
              1 - v/c

Transverse motion and gravity also produce/affect redshift.

Redshift derived from absorption lines is termed absorption redshift (zabs) and from emission lines is termed emission redshift (zem). A difference between the two implies distance and/or velocity differences between the emitting and absorbing material, and can motivate some analysis to determine the "true" cosmological redshift.

When a body's redshift is determined, assuming the redshift is cosmological allows a distance estimate to be calculated using the redshift and the Hubble constant (70 km/s/Mpc). Below are some calculated values. "Linear" was calculated using a simple linear approximation (workable for z less than 0.1) and "Relativistic" takes special relativity into account (the above formula) and is suitable for all redshifts. "GYears" (for gigayears) is how far in the past we're viewing the body and is also its distance in billions of light-years.

zVelocity Mpc GYearsVelocity Mpc GYearsexcess
0.013000km/s 43Mpc 0.1GY2985km/s 43Mpc 0.1GY0.50%
0.026000km/s 86Mpc 0.3GY5940km/s 85Mpc 0.3GY1.01%
0.039000km/s 129Mpc 0.4GY8865km/s 127Mpc 0.4GY1.52%
0.0412000km/s 171Mpc 0.6GY11760km/s 168Mpc 0.5GY2.04%
0.0515000km/s 214Mpc 0.7GY14625km/s 209Mpc 0.7GY2.56%
0.0618000km/s 257Mpc 0.8GY17461km/s 249Mpc 0.8GY3.09%
0.0721000km/s 300Mpc 1.0GY20267km/s 290Mpc 0.9GY3.62%
0.0824000km/s 343Mpc 1.1GY23043km/s 329Mpc 1.1GY4.15%
0.0927000km/s 386Mpc 1.3GY25789km/s 368Mpc 1.2GY4.69%
0.130000km/s 429Mpc 1.4GY28507km/s 407Mpc 1.3GY5.24%
0.260000km/s 857Mpc 2.8GY54098km/s 773Mpc 2.5GY10.91%
0.390000km/s 1286Mpc 4.2GY76952km/s 1099Mpc 3.6GY16.96%
0.4120000km/s 1714Mpc 5.6GY97297km/s 1390Mpc 4.5GY23.33%
0.5150000km/s 2143Mpc 7.0GY115385km/s 1648Mpc 5.4GY30.00%
0.6180000km/s 2571Mpc 8.4GY131461km/s 1878Mpc 6.1GY36.92%
0.7210000km/s 3000Mpc 9.8GY145758km/s 2082Mpc 6.8GY44.07%
0.8240000km/s 3429Mpc 11.2GY158491km/s 2264Mpc 7.4GY51.43%
0.9270000km/s 3857Mpc 12.6GY169848km/s 2426Mpc 7.9GY58.97%
1300000km/s 4286Mpc 14.0GY180000km/s 2571Mpc 8.4GY66.67%
1.5450000km/s 6429Mpc 21.0GY217241km/s 3103Mpc 10.1GY107.14%
2600000km/s 8571Mpc 28.0GY240000km/s 3429Mpc 11.2GY150.00%
3900000km/s 12857Mpc 41.9GY264706km/s 3782Mpc 12.3GY240.00%
41200000km/s 17143Mpc 55.9GY276923km/s 3956Mpc 12.9GY333.33%
51500000km/s 21429Mpc 69.9GY283784km/s 4054Mpc 13.2GY428.57%
61800000km/s 25714Mpc 83.9GY288000km/s 4114Mpc 13.4GY525.00%
72100000km/s 30000Mpc 97.8GY290769km/s 4154Mpc 13.5GY622.22%
82400000km/s 34286Mpc 111.8GY292683km/s 4181Mpc 13.6GY720.00%
92700000km/s 38571Mpc 125.8GY294059km/s 4201Mpc 13.7GY818.18%
103000000km/s 42857Mpc 139.8GY295082km/s 4215Mpc 13.7GY916.67%
113300000km/s 47143Mpc 153.8GY295862km/s 4227Mpc 13.8GY1015.38%
123600000km/s 51429Mpc 167.7GY296471km/s 4235Mpc 13.8GY1114.29%
133900000km/s 55714Mpc 181.7GY296954km/s 4242Mpc 13.8GY1213.33%
144200000km/s 60000Mpc 195.7GY297345km/s 4248Mpc 13.9GY1312.50%
154500000km/s 64286Mpc 209.7GY297665km/s 4252Mpc 13.9GY1411.76%
10030000000km/s 428571Mpc 1397.8GY299941km/s 4285Mpc 14.0GY9901.96%


Referenced by:
Alcock-Paczyński effect
astronomical quantities
Balmer series
band shifting
Balmer-break galaxy (BBG)
brightest cluster galaxy (BCG)
blind survey
Baryon Oscillation Spectroscopic Survey (BOSS)
Calán/Tololo Survey
Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS)
carbon (C)
CCAT-prime (CCAT-p)
Cepheid variable (CEP)
CfA Redshift Survey
Canada-France Redshift Survey (CFRS)
Canadian Hydrogen Intensity Mapping Experiment (CHIME)
cosmic infrared background (CIB)
ionized carbon fine structure line ([CII])
cluster radius
cosmic microwave background (CMB)
carbon monoxide (CO)
Carbon Monoxide Mapping Array (COMA)
cosmic distance ladder
cosmological time dilation
cosmological zoom simulation
Cosmic Evolution Survey (COSMOS)
critical density (ρc)
Carnegie Supernova Project (CSP)
dark age
data cube
direct collapse black hole (DCBH)
deep field (DF)
deep survey
Dark Energy Survey (DES)
Dark Energy Spectroscopic Instrument (DESI)
distance modulus (u)
Extended Groth Strip (EGS)
emission line galaxy (ELG)
emission line
ESO Nearby Abell Cluster Survey (ENACS)
epoch of reionization (EOR)
epoch of galaxy formation
extremely red object (ERO)
Faber-Jackson relation (FJR)
Faint Infrared Grism Survey (FIGS)
first galaxies
galaxy cluster (CL)
galaxy merger
galaxy power spectrum
Galaxy Zoo
gas fraction estimation
Green Bank Telescope (GBT)
Gemini Observatory
Giant Metrewave Radio Telescope (GMRT)
gravitational redshift
Great Attractor
great debate
Great Wall
Gunn-Peterson trough
Hα survey
Hamburg/ESO Survey (HE)
Hercules-Corona Borealis Great Wall (Her-CrB GW)
Herschel Redshift Survey (HeRS)
Hoag's Object
hot DOG
Hubble constant (H0)
Hubble diagram
Hubble Ultra-Deep Field (HUDF)
intensity mapping
K correction
Lyman-alpha emitter (LAE)
Lambda-CDM model (ΛCDM)
Lyman-break galaxy (LBG)
line broadening
Large Millimeter Telescope (LMT)
Low-frequency Array (LOFAR)
large quasar group (LQG)
luminous red galaxy (LRG)
luminosity distance (dL)
luminosity function (LF)
Lyman-alpha forest
Multi-Epoch Nearby Cluster Survey (MENeaCS)
Molecular Deep Field
Murchison Widefield Array (MWA)
near infrared (NIR)
Origins Space Telescope (OST)
Palomar Four-filter Survey (PC)
P Cygni profile
peak star-formation epoch
photometric redshift (photo-z)
quasar (QSO)
redshift-angular size relation
redshift-magnitude relation
redshift space
redshift survey
rest wavelength
Rossiter-McLaughlin effect (RM effect)
Supernova Cosmology Project (SCP)
Sloan Digital Sky Survey (SDSS)
star formation history (SFH)
star formation rate (SFR)
star-formation rate stellar-mass ratio
Spitzer HETDEX Exploratory Large Area Survey (SHELA)
submillimeter galaxy (SMG)
Supernova Legacy Survey (SNLS)
spectral feature
spectral line
Swope Supernova Survey (SSS)
survey depth
Sachs-Wolfe effect (SWE)
systemic velocity
3C 273
3C 295
3C 48
time dilation
Tomographic Ionized-carbon Mapping Experiment (TIME)
21cm experiment
21cm line
2dF Galaxy Redshift Survey (2dFGRS)
ultraluminous infrared galaxy (ULIRG)
USS Sources
VIMOS-VLT Deep Survey (VVDS)
X-ray luminosity function (XLF)