Page last updated Mar 28, 2016
Note added June 12, 2013: This page is essentially a reminder to myself to eventually post a list of quasars which happen to be shown on the images posted in my Sky Atlas. Eventually the Atlas will contain at least twenty thousand images of the regions near various NGC/IC/PGC objects, and as a result there will be something of the order of a hundred thousand cataloged background objects that happen to be in the field of view. A number of those are bound to be quasars, and if and when when I get around to labeling those background objects, any quasars will be listed on this page, with links to the images showing their locations.
There are a number of problems involved in determining the "correct" distance to very distant objects such as quasars, and the start of this page includes some notes (again, primarily as a reminder to myself) about those problems, and when I have properly addressed those problems in the text of this page, I will remove this paragraph.
The first paragraph below suggests that all quasars currently shown and labeled on images in the Sky Atlas are in the list below. That is not true. There are over a dozen already shown and labeled, and only the first three are listed below, due to the fact (indicated by the large number of question marks used in place of actual numbers) that I have yet to deal with the problems involved in calculating their distances. All three are shown in the wide-field image of NGC 7, which is the target for the links attached to their "names".
(the material below was entered prior to the notes above, and does not mention those caveats)
Even though still in its earliest stages, this site's Sky Atlas includes a few images showing the locations of various quasars. This page represents a summary of those quasars, along with a smattering of additional information and images, and links to the images which led to their being listed here. For now, the listing is in order of right ascension, but the page may be considerably revised as the Sky Atlas nears completion.
Note: An examination of quasars with different redshifts z will reveal a paradoxical result -- quasars with larger redshifts, which must have been further away than quasars with smaller redshifts at the time their light was emitted, have calculated distances which are less than those of quasars with smaller redshifts. The reason for this is that we see the higher-redshift quasars at a time when the Universe was smaller; so even though they were further out in comparison to the overall size of the Universe, they were closer to us at that time than quasars that we observe as they were at later dates.
Names for distances involved in high-redshift distance calculations
(Values depend upon theoretical models of the nature of the Universal expansion)
Angular diameter distance (a poor name, but the one used in iCosmos): For "nearby" objects (z << 1.5), the approximate distance of the object at the time its light was emitted; it can be used with the apparent angular size of an object to estimate its true size, whence its name. For distant objects such as quasars, the angular diameter distance is essentially meaningless, as it gives a distance larger than the size of the observable Universe at that time; and since quasars have no angular size it is essentially useless, anyway. So DO NOT USE THIS DISTANCE FOR OBJECTS WITH VERY LARGE VALUES FOR Z.
Co-moving distance (requires some relativity theory to explain): The current distance of the object (determined from iCosmos). For almost all quasars, this is larger than the current size of the "observable" Universe, meaning that the light now being emitted by those objects will never reach our part of the Universe (the intervening space already having an overall expansion rate greater than the speed of light).
Look-back time: The time it took the light to get from the object to us (determined from iCostmos by subtracting the age of the Universe at the time the light was emitted from the current age)
Age of the Universe at the time the light by which we see the objects was being emitted (determined directly from iCosmos)
Assumption: The Universe started at zero size, but after a brief period of Inflation (around 10 to the minus 43 seconds), which made it much larger (how large depends on who you talk to), expanded at more "reasonable" rates. For the first few billion years, the mass of the Universe created a gravitational force large enough to slow the expansion, so the initial rate of expansion gradually decreased; but around 6 to 7 billion years ago the tendency of empty space to expand (so called "dark energy") became equal to the gravitational force, and the rate of expansion remained about the same for a while. The continued expansion of space has gradually made the effects of gravity less and less important, and as a result the expansion of the Universe is asymptotically approaching the "natural" rate at which empty space expands in the complete absence of gravity. The theoretical model which best matches this scenario is the basis for the calculations below. In the numerical version of that model used to produce the calculated results listed below, the current expansion rate of the Universe (the Hubble constant) is assumed to be about 70 km/sec/Mpc (the actual value is probably within 2 or 3% of that value), the mass of the Universe is assumed to be about 30% of the "critical" mass at which gravity would forever slow or balance the tendency of empty space to expand, and the "dark energy" corresponding to the expansion of space is assumed to be equivalent to about 70% of the "critical" mass, so the total mass equivalence is 100% of the "critical" mass. This is referred to as a "flat" Universe model. In reality, the Universe is probably "open", and will expand a little faster in the far distant future than this model predicts; but at the current time, the data available are not capable of adequately distinguishing one variation on the model from another, so this is the best that can be done for now.
Note: The redshifts which we observe for very distant objects consist of two parts -- (1) a redshift corresponding to the recessional velocity of the object (as a result of the expansion of the Universe at the time its light was emitted), PLUS (2) an "expansion" of the light (an increase in the redshift) due to the expansion of the space through which the light passed during the time it took to reach us. For instance, if an object was 2 billion light years away when the Universe was only 4 billion years old, it would have started with a redshift of 0.5 (the same as its distance, compared to the "size" of the Universe at that time). But let's suppose that the light took 9.5 billion years to get here. In that case, the space between here and its original position would have expanded by 4.25 times during its journey, increasing its redshift by that much, so that its current redshift would be 2.125.
In other words, doing a simplistic calculation, let t be the age of the Universe at the time the light left the quasar. Let T be the time it took the light to get here. let x be the distance the quasar had when it emitted the light by which we see it. Then the original redshift is x/t, and the expanded redshift is x/t times T/t, or xT/t-squared. Therefore x = zt-squared/T.
So, if z = 1.591, t = 3.991, and T = 13.4694 - 3.9913 = 9.4781, x = 1.591 * 3.991 * 3.991 / 9.4781 = 2.674 billion light years (so z0 = 2.674/3.991 = 0.670, and the expansion due to the light travel time is 2.375
The italicized material above is a simplistic effort to visualize the situation. In the results below, certain things come directly out of the theoretical model, and do not require that interpretation. Namely: The current distance (the co-moving distance), the time it took the light to get here (the "look-back" time), and the age of the Universe at the time the light left the quasar are all directly calculated by iCosmos. However, the distance of the quasar at the time its light was emitted is calculated from the iCosmos numbers using the italicized equations, and even if "correct" (which is obviously a matter of some debate) would not be accepted by some other writers.
A 20th-magnitude quasar in Sculptor (RA 00 08 02.7, Dec -29 56 32)
Based on a redshift of 476970 km/sec (z = 1.591), we see this quasar as it was about 9.5 billion years ago, when the Universe was only about 4 billion years old (which means that objects at the "edge" of the "observable Universe" were only 4 billion light years away). At that time, the quasar was only about 2.7 billion light years away, but between its recessional velocity at that time (about 2/3 the speed of light) and the subsequent expansion of the space between it and us (which would have increased as it moved further away), it is now about 14.8 billion light years away, which is beyond the "edge" of the currently "observable Universe". As a result, we will never see the light it is currently emitting, as the space between here and there is expanding faster than its light can approach us.
A 21st-magnitude quasar in Sculptor (RA 00 08 26.4, Dec -29 57 50)
Based on a redshift of ? km/sec (z = 2.038), about ? billion light years away at the time the light by which we see it left it, ? billion years ago. During that time, the space between us and the original position of the quasar expanded by ? billion light years, causing the difference between the two values. Throughout that time the quasar was carried to even greater distances, leading to an even greater increase in its distance as a result of the expansion of that extra space, and it is now about ? billion light years away. As a result, any radiation now being emitted by it is being carried away from us by the expansion of the intervening space at more than the speed of light, so it now lies beyond the edge of the "observable" Universe.
A 20th-magnitude quasar in Sculptor (RA 00 08 27.4, Dec -29 54 23)
Based on a redshift of z = 2.061, 2QZ J000827.4-295423 was about 5765 million light years away at the time the light by which we see it left it, 10570 million years ago. During that time the space between us and the original position of the quasar expanded by about 4800 million light years, causing a 4800 million year delay in the light's arrival. Throughout the 10570 million years it took for its light to reach us the expansion of the intervening space carried the quasar to even greater distances, and it is now about 17650 million light years away. As a result the space between us and the quasar is expanding at a cumulative speed greater than the speed of light, and any radiation now being emitted by it will never reach us, so it is now beyond the edge of the "observable" Universe.
A 19th-magnitude quasar in Cetus (RA 00 56 31.2, Dec -09 57 58)
Based on a redshift of z = 1.654342, Q005631.24-095757.5 was about 5840 million light years away at the time the light by which w see it left it, 9815 million years ago. During that time the space between us and the original position of the quasar expanded by about 3975 million light years, causing a 3975 million year delay in the light's arrival. Throughout the 9815 million years it took for its light to reach us the expansion of the intervening space carried the quasar to even greater distances, and it is now about 15500 million light years away. As a result the space between us and the quasar is expanding at a cumulative speed greater than the speed of light, and any radiation now being emitted by it will never reach us, so it is now beyond the edge of the "observable" Universe.