3C 66A

3C 66A is a blazar^[1][2] located in the constellation Andromeda.

3C 66A
Hubble Legacy Archive WFPC2 image of 3C 66A (brightest object on the far right)
Observation data (Epoch J2000)
Constellation	Andromeda
Right ascension	02h 22m 39.612s[1]
Declination	+43° 02′ 07.80″[1]
Redshift	0.444[1][2]
Distance	4.5 billion light-years (Light travel time)[2] 5.4 billion light-years (present)[2]
Type	BLLAC[2]
Apparent magnitude (V)	15.5[1][2]
Other designations
2E 558, 2EG J0220+4228, B3 0219+428A, QSO B0219+4248[1]
See also: Quasar, List of quasars

The "distance" of a far away galaxy depends on the distance measurement used. With a redshift of 0.444,^[1][2] light from this active galaxy is estimated to have taken around 4.5 billion years to reach Earth.^[2] But as a result of the expansion of the Universe, the present (co-moving) distance to this galaxy is about 5.4 billion light-years (1647 Mpc).^[2] Even at this great distance this blazar has an apparent magnitude of about 15.5.^[1] Although 0.444 is used as the common redshift value, 0.3347 is a new strict lower limit "inferred through observing the far-UV absorption by the low-z IGM."^[3]

3C 66A underwent an optical outburst in 2007 August, as monitored by the Tuorla blazar monitoring program.^[4] The event was monitored by the Whole Earth Blazar Telescope project.