At the turn of the sixteenth century Tycho Brahe and Johannes Kepler made single pinhole measurements of the solar diameter. Their accuracy was limited by diffraction (unknown to them) and the motion of the image on the screen. We discuss how two pinholes built on the same mask can be used to bypass all the problems inherent in the single pinhole approach. The distance at which the two images of the Sun are in contact is the only measurement needed, and the experimental accuracy is much better than measuring the diameter of a single moving image. We obtained 0.5% accuracy, sufficient to follow the angular variations of the solar diameter due to the motion of the Earth in its orbit.
REFERENCES
1.
Tycho Brahe, Opera Omnia, edited by J. L. E. Dreyer (Hauniæ, 1913), Vol. XII, pp. 108–118.
2.
Johannes Kepler, Ad Vitellionem Paralipomena, Quibus Astronomiæ Pars Optica Traditur (Frankfurt, 1604), Chap. IX.
3.
C.
Sigismondi
and F.
Fraschetti
, “Measurements of the solar diameter at Kepler’s time
,” The Observatory
121
, 380
–385
(2001
).4.
Kepler can be considered to be the inventor of the camera obscura and was the first to describe its principles (see Ref. 2). A camera obscura is a dark room where a pinhole is open on one wall. It projects an upside-down image of what is visible through the pinhole on the opposite wall. The formation of the image in a photographic camera is based on the same principle.
5.
P. R. Bevington and D. K. Robinson, Data Reduction and Error Analysis for the Physical Sciences (McGraw–Hill, New York, 1992).
6.
The Encyclopedia Britannica, 1911. See http://www.1911ency.org/. The original idea of the heliometer is attributed to the Danish astronomer Olaus Römer (1644–1710), although the date of the invention, 1768, given in the Web site of the scanned version of the 1911 Britannica is accidentally incorrect.
7.
See http://scienceworld.wolfram.com/biography/Bessel.html
8.
H. C.
Chiu
, E.
Maier
, K. H.
Schatten
, and S.
Sofia
, “Solar disk sextant optical configuration
,” Appl. Opt.
23
, 1230
–1234
(1984
).9.
S.
Sofia
, H. C.
Chiu
, E.
Maier
, K. H.
Schatten
, P.
Minott
, and A. S.
Endal
, “Solar disk sextant
,” Appl. Opt.
23
, 1235
–1237
(1984
).10.
W.
Schur
and L.
Ambronn
, “Die Messungen des Sonnendurchmessers
,” Astron. Mittheilungen der Königlichen Sternwarte zu Göttingen
7
, 17
–60
(1905
).11.
See http://www.clearskyinstitute.com/xephem/ for information about XEPHEM.
This content is only available via PDF.
© 2002 American Association of Physics Teachers.
2002
American Association of Physics Teachers
AAPT members receive access to the American Journal of Physics and The Physics Teacher as a member benefit. To learn more about this member benefit and becoming an AAPT member, visit the Joining AAPT page.
