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UDF 423 is the Hubble Ultra Deep Field (UDF) identifier for a distant spiral galaxy. With an
UDF 423 is the Hubble Ultra Deep Field (UDF) identifier for a distant spiral galaxy. With an apparent magnitude
Apparent magnitude () is a measure of the Irradiance, brightness of a star, astronomical object or other celestial objects like artificial satellites. Its value depends on its intrinsic luminosity, its distance, and any extinction (astronomy), ...
of 20, UDF 423 is one of the brightest galaxies in the HUDF and also has one of the largest apparent sizes in the HUDF.
Distance measurements
The "distance" of a far away galaxy depends on how it is measured. With aredshift
In physics, a redshift is an increase in the wavelength, and corresponding decrease in the frequency and photon energy, of electromagnetic radiation (such as light). The opposite change, a decrease in wavelength and increase in frequency and e ...
of 1, light from this galaxy is estimated to have taken around 7.7 billion
Billion is a word for a large number, and it has two distinct definitions:
* 1,000,000,000, i.e. one thousand million, or (ten to the ninth power), as defined on the short scale. This is now the most common sense of the word in all varieties of ...
years to reach Earth. However, since this galaxy is receding from Earth, the present comoving distance
In standard cosmology, comoving distance and proper distance (or physical distance) are two closely related distance measures used by cosmologists to define distances between objects. ''Comoving distance'' factors out the expansion of the univ ...
is estimated to be around 10 billion light-year
A light-year, alternatively spelled light year (ly or lyr), is a unit of length used to express astronomical distances and is equal to exactly , which is approximately 9.46 trillion km or 5.88 trillion mi. As defined by the International Astr ...
s away. In context, Hubble is observing this galaxy as it appeared when the Universe was around 4.9 billion years old.
See also
*List of Deep Fields
In astronomy, a deep field is an image of a portion of the sky taken with a very long exposure time, in order to detect and study faint objects. The depth of the field refers to the apparent magnitude or the Spectral flux density, flux of the fai ...
References
Fornax Spiral galaxies Hubble Space Telescope 00423 {{Spiral-galaxy-stub