Magnitudes and distance
radius of observable Universe ( Ym). Ym = 10+26 m, hundred yottametres. distance to quasar 3C (50 Ym). distance to quasar 3C (30 Ym);. magnitude calculator, brightness calculator, absolute magnitude, apparent magnitude, advanced magnitude calculator, advanced astronomy magnitude calculator. For example the Earth is one astronomical unit of distance from the Sun. If it were at 2 of the distance. Knowing these relationships, we can set up a formula. The brightness classes are now known as apparent magnitudes, and are denoted brighter than another, the intensity of the two stars may differ by orders of magnitude. . The relationship between distance, apparent magnitude and absolute.
Inthe mathematician John Keill described the ancient naked-eye magnitude system in this way: The fixed Stars appear to be of different Bignesses, not because they really are so, but because they are not all equally distant from us.
Hence arise the Distribution of Stars, according to their Order and Dignity, into Classes; the first Class containing those which are nearest to us, are called Stars of the first Magnitude; those that are next to them, are Stars of the second Magnitude For all the other Stars, which are only seen by the Help of a Telescope, and which are called Telescopical, are not reckoned among these six Orders.Magnitude relation between distance and displacement of the body(class9th-motion-part05)
Altho' the Distinction of Stars into six Degrees of Magnitude is commonly received by Astronomers; yet we are not to judge, that every particular Star is exactly to be ranked according to a certain Bigness, which is one of the Six; but rather in reality there are almost as many Orders of Stars, as there are Stars, few of them being exactly of the same Bigness and Lustre. And even among those Stars which are reckoned of the brightest Class, there appears a Variety of Magnitude; for Sirius or Arcturus are each of them brighter than Aldebaran or the Bull's Eye, or even than the Star in Spica; and yet all these Stars are reckoned among the Stars of the first Order: And there are some Stars of such an intermedial Order, that the Astronomers have differed in classing of them; some putting the same Stars in one Class, others in another.
And therefore it is not truly either of the first or second Order, but ought to be ranked in a Place between both. Bright "first magnitude" stars are "1st-class" stars, while stars barely visible to the naked eye are "sixth magnitude" or "6th-class".
The system was a simple delineation of stellar brightness into six distinct groups but made no allowance for the variations in brightness within a group. Tycho Brahe attempted to directly measure the "bigness" of the stars in terms of angular size, which in theory meant that a star's magnitude could be determined by more than just the subjective judgment described in the above quote.
However, early telescopes produced a spurious disk-like image of a star that was larger for brighter stars and smaller for fainter ones.
Astronomers from Galileo to Jaques Cassini mistook these spurious disks for the physical bodies of stars, and thus into the eighteenth century continued to think of magnitude in terms of the physical size of a star.
On this basis the spectral irradiance usually expressed in janskys for the zero magnitude point, as a function of wavelength, can be computed. With the modern magnitude systems, brightness over a very wide range is specified according to the logarithmic definition detailed below, using this zero reference.
In practice such apparent magnitudes do not exceed 30 for detectable measurements. The brightness of Vega is exceeded by four stars in the night sky at visible wavelengths and more at infrared wavelengths as well as the bright planets Venus, Mars, and Jupiter, and these must be described by negative magnitudes.
Apparent magnitude - Wikipedia
Negative magnitudes for other very bright astronomical objects can be found in the table below. Astronomers have developed other photometric zeropoint systems as alternatives to the Vega system.
The most widely used is the AB magnitude system,  in which photometric zeropoints are based on a hypothetical reference spectrum having constant flux per unit frequency intervalrather than using a stellar spectrum or blackbody curve as the reference.
The AB magnitude zeropoint is defined such that an object's AB and Vega-based magnitudes will be approximately equal in the V filter band. This nebula has an apparent magnitude of 8. A graph of apparent magnitude against brightness As the amount of light actually received by a telescope is reduced by transmission through the Earth's atmosphereany measurement of apparent magnitude is corrected for what it would have been as seen from above the atmosphere.