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Opik (Opik), Ernst Julius (1893–1985)

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Opik (Opik), Ernst Julius (1893–1985)

Born in Estonia, Opik studied at Moscow University,

and helped establish Turkestan University in Tashkent,

becoming the Astronomer (director) at Tartu Observatory

in Estonia. He ﬂed the Red Army by horse cart during

the Second World War and went to Armagh Observatory

(Northern Ireland) in 1948. His wide-ranging interests are

reﬂected in his discoveries and theories. These include

the discovery of degenerate stars, e.g. white dwarfs, in

his calculation of the density of o 2 Eridani (1915). He

calculated the distance of M31 as 450 000 parsecs from the

Sun (1922). He computed by hand evolutionary models

of main-sequence stars into giants (1938) over a decade

earlier than the computer computations of HOYLE and

SCHWARZSCHILD . He predicted the density of craters on the

surface of Mars, which was conﬁrmed 15 years later by

planetary probes. He put forward an unproven theory

of the Ice Ages based on a calculation of changes in the

convection in the internal structure of the Sun rather than

MILANKOVITCH cycles.

Brunel Road, Houndmills, Basingstoke, Hampshire, RG21 6XS, UK Registered No. 785998

and Institute of Physics Publishing 2001

Dirac House, Temple Back, Bristol, BS1 6BE, UK

Ångstr om, Anders Jonas (1814–74)

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Ångstr om, Anders Jonas (1814–74)

Physicist, born in Lodg o, Sweden. He was keeper of the

observatory and professor at Uppsala where he studied

heat, magnetism and optics and examined the spectra of

the Sun and auroras. His name is commemorated with

the angstrom unit ,10 − 10 m, which is used for measuring

wavelengths of light and x-rays, and the separation of

atoms in molecules and crystals.

Brunel Road, Houndmills, Basingstoke, Hampshire, RG21 6XS, UK Registered No. 785998

and Institute of Physics Publishing 2001

Dirac House, Temple Back, Bristol, BS1 6BE, UK

61 Cygni

E NCYCLOPEDIA OF A STRONOMY AND A STROPHYSICS

61 Cygni

The star 61 Cygni is important because of its large proper

motion, ﬁrst measured at the Palermo Observatory by

Giuseppe Piazzi (1746–1826). The star became popularly

known as ‘Piazzi’s ﬂying star’. Its measured annual proper

motion of 5.23 is still the seventh largest known, and is

the largest for a naked-eye star (apparent magnitude 4.8).

This star was also the ﬁrst to have its annual parallax

reliably determined, by Friedrich Bessel (1784–1846).

Bessel’s measurement of 0.314 , made at K onigsberg with

Fraunhofer’s 6.25 inch heliometer in 1838, compares quite

well with the modern value of 0.286 . Determinations of

stellar parallax made in the same year by other observers

were far less accurate. It is the eleventh closest star, at a

distance of 11.4 light-years.

61 Cygni is also a well-known binary system, with

a period of 653.3 years. Its components are currently

separated by 30.3 at position angle 150 ◦ . The primary

star 61 Cyg A is an orange dwarf, spectral type K5V,

of apparent magnitude 5.20 and absolute magnitude 7.5.

Its companion 61 Cyg B is also an orange dwarf, of

spectral type K7V, with an apparent magnitude of 6.05

and absolute magnitude 8.3. The system is reputed

to be the most extensively observed double star, some

thousands of visual observations being supplemented by

more than 34 000 photographic plates. Precise astrometric

measurements of these plates have indicated that the

system has at least one invisible component, believed to

be a planet of similar mass to Jupiter, and perhaps as many

as three, with orbital periods of between 5 and 12 years.

Brunel Road, Houndmills, Basingstoke, Hampshire, RG21 6XS, UK Registered No. 785998

and Institute of Physics Publishing 2001

Dirac House, Temple Back, Bristol, BS1 6BE, UK

Abastumani Astrophysical Observatory

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Abastumani Astrophysical

Observatory

The Abastumani Astrophysical Observatory (AbAO)—

longitude, 42.83; latitude, 41.81 degrees—was founded in

1932. It is located in Abastumani, in the south-west part

of the Republic of Georgia, 250 km west of the capital city

Tbilisi, on the top of Mount Kanobili at 1700 m.

AbAO’s primary mission is to enable astronomers

of the former Soviet Union to carry out high-quality

observations. The average number of clear nights is

130 per year with 25% of seeings smaller than one

arcsec. At present, about 100 staff members work at the

Observatory in six departments and four laboratories. The

Observatory’s main facilities are 125 cm Ritchey–Chretien

and 70 cm meniscus telescopes.

The major research areas are accretion disks and

pulsars astrophysics, solar system cosmogony, objec-

tive prism spectroscopy, low-amplitude short-period vari-

ables, AGNs variability, solar physics, solar–terrestrial

phenomena and atmospheric physics.

For further information see

http://gamma.bu.edu/webt/abastumani.

Brunel Road, Houndmills, Basingstoke, Hampshire, RG21 6XS, UK Registered No. 785998

and Institute of Physics Publishing 2001

Dirac House, Temple Back, Bristol, BS1 6BE, UK

Abbe, Ernst (1840–1905)

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Abbe, Ernst (1840–1905)

Born in Eisenach, Grand Duchy of Saxe-Weimar-Eisenach

(now Germany), Abbe became director of the observatory

at Jena and research director of the CARL ZEISS optical works

in Jena. He discovered the Abbe sine condition , which

describes a lens that will form an image, without defects

of coma and spherical aberration. His mathematical

treatment founded the present-day science of optics.

Brunel Road, Houndmills, Basingstoke, Hampshire, RG21 6XS, UK Registered No. 785998

and Institute of Physics Publishing 2001

Dirac House, Temple Back, Bristol, BS1 6BE, UK

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