Victor d'Avila, Eugenio Reis Neto, Alissandro Coletti, Luis Carlos Oliveira, Victor Matias, Alexandre Humberto Andrei, Jucira Lousada Penna, Sergio Calderari Boscardin, Costantino Sigismondi
The heliometer of Fraunhofer in Koenigsberg (1824) is a refractor in which
the lens is split into two halves to which is applied a linear displacement
along the cut. Later in 1890s a variation of the heliometer has been realized
in Goettingen using a beam splitting wedge: these methods were both subjected
to chromatic and refractive aberrations; the second configuration being much
less affected by thermal fluctuations. The mirrored version of the heliometer
conceived at the Observatorio Nacional of Rio de Janeiro overcome these
problems: the two halves of the vitrified ceramic mirror split at a fixed
heliometric angle produce the two images of the Sun exempt of chromatisms and
distortions. The heliometer of Rio is a telescope which can rotate around its
axis, to measure the solar diameter at all heliolatitudes. A further
development of that heliometer, now under construction, is the annular
heliometer, in which the mirrors are concentric, with symmetrical Point Spread
Functions. Moreover the location of the Observatory of Rio de Janeiro allows
zenithal observations, with no atmospheric refraction at all heliolatitudes, in
December and January.
View original:
http://arxiv.org/abs/1112.5871
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