The transit of Venus : its meaning and use / by T.H. Budd.

  • Budd, T. H. (Thomas Hayward)
Date:
1875
Catalogue details

Licence: Public Domain Mark

Credit: The transit of Venus : its meaning and use / by T.H. Budd. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    from us by comparing its apparent height, or the ^ angle it makes with the eye, with its actual height. These facts being apparent with regard to the tree we are ready of course to understand their applicability to the Sun, that is to say, we are ready to admit that if i we can ascertain the actual diameter of the Sun, we j can, by comparing it with its apparent diameter, ascer- \ tain its distance from us. I should point out that j supposing the circle of the heavens to be divided into j 360 degrees like our theodolite disc, the Sun does ^ not occupy so much as one degree of it. ^ It has been ascertained that the distances of Venus \ from the Sun and the distance of the Earth from the ^ Sun are in proportion of about 72 to 100 ; that is to say, | if Venus is 72,000,000 of miles from the Sun the | Earth is 100,000,000 of miles from it. When Venus, \ therefore, passes across the Sun’s disc, as it will do on ] its transit, and one person is looking at it from the extreme North point of the Earth, and another from the extreme South, it is obvious that the two persons cannot see her projected on the Sun in the same place. In other words, the observer at the North point of the Earth will see her lower down on the face of the Sun than the observer at the South can. If it could be seen from both points at once (which, of course, is impossible), it would appear to the eye as two planets instead of one crossing the Sun, and their tracks would make a sort of band across the Sun. Now the know- ledge of the length of our base line—in other words the