web metrics

We have received a couple of letters in response to our articles on aberration in the last two issues. The most extensive is from Dick Elmendorf. I shall quote him point by point and my response will appear in italics between the points:

(1) How do you know you are pointing a telescope “forward" to see a star, as is described in the stovepipe analogy? Aren't you just pointing the telescope so as to see the star, without knowing whether that is forward, backward, sideways or straight-on? In other words, how do you know where the star is in the first place?

Bradley's original telescope was fixed immovably to the earth. Modern telescopes are mounted on a pier which is inserted into the earth down to bedrock. Part of the telescope includes a series of gauges called setting circles. If the setting circles are large enough, a resolution of a minute of arc or less is easily achieved. The most fundamental of all position determination instruments, however, was the transit circle. Here the telescope could only move along a north-south meridian. The error of a typical transit circle observation is only 0".2, one hundredth the size of aberration. Aberration showed up in two forms there. First of all, in a yearly north-south variation as the star crossed the meridian and secondly, as a variation in the time when the star crossed the meridian. For half the year the star was early, and the other half it was behind the mean transit time. A third means involves occultation timings, of which more later.

(2) How do you know that light is particles, and that the stovepipe analogy is even valid?

Whether or not light consists of particles or waves, experiments in the lab (e.g., those of Fresnell) show that aberration is real.

(3) Are the same stars used for determining both aberration and parallax, or are they different stars? If they are different stars in any particular case, aren't you just assuming that both categories of stars rotate in unison and that the phase difference is therefore a meaningful argument?

As seen under point (1), there are no reference stars used for determining aberration. That determination is made from a coordinate system rigidly fixed on the earth. To measure parallax a star's position is measured with respect to the stars seen around it. Sometimes the star is closer than those faint, presumably background stars, sometimes it is not. It is important to realize that the measurements are repeatable, that a star always behaves the same way with respect to the background stars. Modern intercontinental interferometry yields consistent results which are 10 to 100 more accurate than the uncertainties encountered 20 years ago. And that includes aberration as well as parallax. In other words, the arguments based on the uncertainties in the measurements which the small universe proponents have been using, were valid twenty years ago, but are no longer valid.

(4) Is having all stars and the sun at equal distances, as is apparently Walter van der Kamp's model, a necessary premise for arguing that aberration is really a parallax. Aren't they two separate issues?

Of course they're separate issues. That's my whole point. For years Walter's been arguing that aberration is parallax, it is not. Walter's argument is equivalent to claiming that holding one's finger a foot in front of one's face, and then alternately opening one eye while closing the other will make the finger jump up and down instead of from left to right.

(5) How do you know that the moon, streetlights and artificial satellites do not exhibit aberration because they are just too close to measure aberration?

See the following.

Two other minor comments are that your dismissal of Walter's distance ideas with that “conspiracy" comment is mere rhetoric la Galileo style, and that your 20".496 figure should better be shown as 20.496", or perhaps as 20.5", in view of the possible error in the figures.

What I said was that since all the planets exhibit aberration, as does the sun, that according to Walter's argument all these objects should be 58 light-days from earth along with the stars. Then I added: “This runs afoul of all evidence, including the U.S.A. and former U.S.S.R.'s space programs unless, of course, one wants to claim some grand conspiracy on the part of scientists and engineers around the world. I know of no such conspiracy, nor any reason to suspect one." I know some do claim that the space program is a hoax, and hence my reference. As for the notation, 20".496 is the correct way to write 20.496 seconds of arc. 20.496" on the other hand, means 20.496 inches. See, for example, the “Explanation" in The American Ephemeris and Nautical Almanac for, e.g., 1968. At this point the uncertainty in less than 0".0005, but in 1968 which was the last reference I have, the uncertainty was no more than 0".001, To contract that to 20".5 implies an uncertainty of 0".1, not 0".001. To change 20".496 to 20".500 is unwarranted, although that is what I would have to have done if I were to take your suggestion. Would you do that as an engineer on a project?

In addition to the letter from Dick Elmendorf, I have had some correspondence with Dr. Thomas Van Flandern of the United State Naval Observatory. Dr. van Flandern is in charge of the lunar occultation observations and is most famous for presenting evidence, based on those occultation results, that the gravitational constant may vary in time. Here are some excerpts.

The…Explanatory Supplement to the Astronomical Ephemeris [of] the 1961 edition…and the 1992 edition…explain the consistent set of rules by which astronomers compute and apply corrections for aberration. A point to note…is that these give a total aberration of less than one arc second for the case of the Moon, since its relative motion is only about 1 km/s, and there is no stellar aberration correction for objects within the Earth's gravitational sphere of influence. The main lunar aberration, the light-time delay, causes an 0".7 offset, which is built into the lunar theory. The numerical example [in the Supplement ] shows that only a tiny additional correction is applied to computed lunar positions for aberration to get the Moon's apparent place.

I have…spoke with George Kaplan at the U.S. Naval Observatory, who is their current expert on aberration. George points out that, if one adopts a solar system barycenter frame of reference [the “barycenter" is the point at which all objects in the solar system balance each other],1 then the Moon, artificial satellites, even radio tower lights can be thought of as having stellar aberration is a sense, even though they are seen without any displacement at their geometric positions in the Earth's frame. In the barycenter frame, one can imagine that stellar aberration almost exactly cancels out the light-time delay effect of the considerable (30 km/s) barycentric motion during the light-time, and gives a net aberration near zero.

So the astronomers' procedures work at all scales. And they work to high precision as VLBI [very-long baseline interferometry, using radiotelescopes on different continents to work together as one giant telescope] observations at the tens of micro-arcseconds [0".00001] level demonstrate. Whether or not these procedures are faithful to the relativity principle is another matter. [It has been] argued that using light-time delay for double stars is not equivalent to using relative velocities. By similar reasoning, neither is the absence of aberrational displacement for near-Earth objects.

For example, when the Moon is observed to occult [pass in front of] a star, the Earth observer sees the star displaced by 20 arc seconds from its geometric position, but sees the Moon nearly at its geometric position. Clearly, whatever displaces the starlight must happen to it before that light passes the Moon's limb, because from there on down the telescope tube the starlight and moonlight must surely remain in synchronization, photon- by-photon. It seems a reasonable inference that stellar aberration occurs at the interface between the Earth's gravitational sphere of influence and the Sun's gravity field. The same argument could be applied to double star systems to explain why their light remains synchronized.

Dr. Van Flandern was kind enough to send me a copy of an article he prepared entitled “Galilean Special Relativity."2 It deals primarily with relativity, but there is a section on aberration. The following paragraph is quoted from page 54 of the article:

In the case of the Sun, there is no motion to consider other than the Earth's orbital velocity. So the Sun's stellar aberration and the change in its position due to lighttime delay are manifestations of a single phenomenon as viewed from the Sun-fixed or the Earth-fixed frames, respectively. Planets have their own orbital motions, so their observed positions can be correctly computed from either their lighttime delay relative to a fixed Earth, or from what is called “planetary aberration" in a Sun-fixed frame.

The article also adds the following statement about the observations of occultations by the moon:

…If a star is occulted by the Moon as it slowly orbits the Earth, the last rays of the star's light are displaced on the sky by 20 arcseconds, whereas the Moon's position is not so displaced. Such a displacement is readily verified, since it makes a difference of about 40 seconds of time in the moment when the star will be seen to disappear from view.

Dr. Van Flandern brings this up to demolish the special theory of relativity's claim that aberration is due to relative motion only, but the statement has geocentric implications.


1 See “Panorama" in Biblical Astronomer 4(67):16 for more on the barycenter of the solar system and there, on the role it plays in orbital theory.

2 Tom van Flandern, 1993. “Galilean Special Relativity," Meta Research Bulletin, 2(4):48-65. Subscriptions to the quarterly are $15 per year and can be ordered by writing to: Meta Research Bulletin, PO Box 15186, Chevy Chase, MD 20825-5186, U.S.A.

Updated on 6 January, 2005 by GDB