Amedeo

Now that nobody has been able to provide a foundation for the objectivity of astronomers or, in particular, for the objectivity of the distance between the earth and a celestial body which appears in visual consciousness now but existed, e.g., a million years ago [and is not present now], I will briefly outline the facts which are hereby alleged to provide the objectivity. They are so obvious -- after they are pointed out -- that many people are not aware of them as being relevant to the question.

A Hypothetical Project:

The task is to measure the distance between the earth, E, and a luminous celestial body, S, which I have been seeing almost every night.

We start with the formula, c [vel. of light] = d/t.

We know the velocity of light (measured in a number of different ways). So, if we know the distance between E and S, we find out how long it takes for the light to go from S to E.

Now, I am assuming for a moment that d has been computed, and that, therefore t = 1 million years. So, this is given: the time lapse between the emission of light and the perception of light [which is the luminous point, S, in my vision], or the time when the e-m waves hit my eyes, is 1 million years. Let the light emitter be called ES.

Now, an astronomer uses the trigonometric parallax to determine the distance between E and ES, which is 1 million years back in time.

For his calculation, he needs to know the distance between two points on one plane of the earth, and angles taken from these two points toward ES. But it is physically impossible to point a theodolite or a telescope toward an invisible thing. So, the sighting is done toward S, the visible celestial point, that is, the visually luminous point where light reaches the eye. The astronomer points towad the arriving light, not the departing light.

The assumption is made that light travels in a straight line. So, the angle, relative to the ground, toward the luminous S is the same as if we were pointing toward ES.. (If SE was slowly moving to the right or some direction, then from night to night there is an observed movement in the same direction. The position of SE is the same as the position of S.)

Considering our visual field, we can estimate the distance from where we being to see outwards to the luminous point as, say, 15 miles. [Of course, we cannot walk in the visual field and measure the distance with a yardstick, but, from daily experience, if we know that a lighthouse on the horizon is 15 miles away, then we can say that the luminous body seems to be 15 miles away or perhaps 20. We cannot make any estimate on the basis of the size of S, because we have no knowledge of the intrinsic , tangible, size of S. And here I am assuming that the size of S has not been computed by any method.) When we see the sun and a single star in the sky, then, by their relative size, S appears to be much farther away than the sun. So, one might even feel that the stars and the like are 100 miles away. (All of these are totally vague estimates, of course). But regardless of our estimate as to how far S is, the angle toward it is the same, whether the distance is 15 miles, or 15 million miles.

The measured angles are objective measurements for points of the earth to the physical ES, even though we handle physical instruments with respect to visual images. The terrestrial distance between two points is mesured with a yardstick or is inferred from such measurements. It's the tangible ground that is measured with a tangible ruler. Of course we see the ruler and the ground which are being measured, but what is important is the INTER-OBJECTIVE measurement: Whether the ground together with the ruler look big or small does not count; the relative length of the ruler and the ground is constant. All the scientific or objective data in Galilean physics are inter-objective in character: between and object and another object [a ruler, a scale, a thrmometer, etc.] All the measurements are in the world of associated tangibles; what is seen or felt (as heavy or hot) is incidental. So, a computed diameter of the earth can be used as the distance between two points, whence the angle to ES are taken. Thus, the trigonometrically computed distance from E to SE is, in value, a tangible distance, not an optic distance (such as the one we estimated earlier).

If we look at certain light experiments to discover its velocity, one starts with a ground measured distance (on which a beam of light will be shot). In all cases, it's the inter-objective data (the Galilean data of the tangible world) that establish objectivity.

The assumed rectilinearity of light is the only datum that has to be established. (In other situations, the perfect constancy of the velocity of light may be questionable.)

Ravear

You really need to learn how to communicate.