Very few auroras were reported bymiddle European observers duringthe years 1793–1818, and there arevery few sunspot data for the samespan. This may be a result of inter-est in solar–terrestrial physics andpossible extreme solar minima,because in this time a limited num-bers of sunspot were also noted.
Although the 18th and 19th cen-turies marked a time of increasinginterest in solar–terrestrial physics,the study of auroras and the Sunwere not mainstream areas forresearch by the astronomers of thetime. For the span 1793–1818 onlya few positive sightings of aurorasare available from European lati-tudes and other parts of the world.Scientific studies would certainlyhave been disrupted by the warsand conflicts of the time, althoughspectacular auroral displays wouldalways have aroused interest.
As can be seen from the table, thereported amount of auroral activitythroughout the span listed isremarkably low. Following Wald-meier (1955), sunspot maximaoccurred in 1788.1, 1805.2 and1816.4, 1829.9, 1837.2. Minimaoccurred in 1784.7, 1798.3, 1810.6,1823.3 and 1833.9. It is of interestthat during 1797–1800 and1807–12, a low relative number ofsunspots was derived (Waldmeier1955). In these timespans the auro-ral reports are mostly missing, notonly in Europe (Dalton 1873, Fritz1883, Cramer 1806, Busse 1815,Parrey 1819, Lampadius 1806), butalso in America (J Lovering and E
Loomis published compilations)only a few reports are available.For 1804 Hallström in Abo andDalton in Manchester noted thevery lowest records of auroras.During their travels in higher north-ern latitudes, Hausmann andLeopold von Buch also reportedvery few auroras during this span(see also Ideler 1832.)
It seems difficult to find a physi-cal explanation for this apparentlylow level of auroral activity duringthis span. Some other known solarminima (e.g. the Spörer and Maun-der Minima) were longer. This min-imum at the end of the 18th centu-ry was short, and may have beencaused by missing observations orvariability in solar cycle length. Thevariability of sunspot cycle lengthhas been often suggested for differ-ent times (e.g. A Brekke 1997, Fritz1881, Gregori 2002, von Steiger2002, Waldmeier 1955). On theother hand, it is of interest that thenumber of observed auroras rosebefore 1793 and after 1819.
In later years, e.g. for the time1830–36, very extensive and brightauroras were noted by Argelanderduring his times in Finland. Intenseauroras were observed in this perioidfrom other parts of the world too.Waldmeier noted a low relativenumber of sunspots in 1821–24, inaccordance with low auroral activity.Between 1819–21 more auroral databecame available. The next reportedminimum was in 1823.3 and themaximum in 1829.9. Both are com-parable with the solar cycle data.
Wilfried Schröder, Geophysical Station,Hechelstrasse 8, D-28777 [email protected]
ReferencesBrekke A 1997 Physics of the polar upperatmosphere Wiley, Chichester.Busse J H (ed.)1815 Robert Halls undBillings Reise in den nordöstlichen Ozeanund durch das nördliche Eismeer Leipzig.Cramer J 1785 Über die Entstehung desNordlichtes Bremen.Dalton J 1873 Meteorological observationsand Essays London.Ephemerides societatis meteorologicaePalatinae Mannheim 1781–92.Fritz H 1881 Das Polarlicht Brockhaus,Leipzig.
Gregori J G 2002 Galaxy-Sun-Earth relationScience Edition.Ideler J L 1832 Über den Ursprung derFeuerkugeln und des Nordlichtes, Berlin.Lampadius W A 1896 Systematischer Grun-driß der Atmosphärologie Graz and Gerlach,Freyberg.Parrey W E (ed.) 1819 Parrey’s Tagebucheiner Entdeckungsreise nach den nördlichenPolargegenden im Jahre 1818 Hamburg.Schröder W 2001 Ber. Gesch. Geophys. undKosm. Physik 2 no. 5.von Steiger R History of solar wind, in SolarVariability and Geomagnetism Science Edi-tion, 78–87.Waldmeier M 1955 Ergebnisse und Prob-leme der Sonnenforschung Akad. Verlagsge-sellschaft, Leipzig.
3.6 June 2003 Vol 44
VIEWS
Auroral data from EuropeThe table summarizes the few data available and includes only data thathave been observed from at least two stations independently. The visualobservations in the table are mainly from middle latitudes (48–65°N).Single observations have been neglected. We note in this period somewidespread auroras (29.1.1780, 2.3.1780, 28.7.1780, 25.11.1780,30.1.1781, 15.2.1781, 25.9.1781, 15.10.1781, 29.3 and 27.4.1783,15.11.1884, 19.3 and 22.3.1886, 13.5, 13.7, 6.10, 31.10 and 26.11.1887,11.2, 23.8 and 21.10.1888, 22.10.1804, 8.2.1817 and 25.9.1827).
Barrie W Jones
Earth-massplanets: updateIn my article in A&G April 2003, Isaid “Gravitational lensing has thepotential now to detect Earth-massplanets”. This potential may nowhave been realized.
In the commonly used exoplanetscatalogue (www.obspm.fr/encycl/catalog.html) there is a short tableheaded “Unconfirmed, controver-sial, or retracted planets”. Thisincludes two stars that might eachhave a planet of less than a fewEarth-masses. The more persuasivecase corresponds to the high magni-
fication gravitational microlensingevent MACHO 98-BLG-35. Bondet al. (2002) conclude that theirbest model has a planet of about anEarth mass at about 1.5 or 2.3 AUfrom the star. These values use rea-sonable assumptions for the massof the lensing star, the radius of thelensed (source) star, and the dis-tances to the source and the lens.
It seems likely that this has beenplaced in the “Unconfirmed…” cat-egory because the Earth-mass inter-pretation is not entirely secure andconfirmation has not yet beenachieved. Sadly, confirmation isunlikely. A second alignmentbetween the lens and a source ishighly improbable, as is the align-ment needed for a planetary transit.
Confirmation by astrometry andDoppler spectroscopy is improbablegiven the estimated 6 kpc distance,and the small effect of an Earth-mass planet at about 1 AU on themotion of its star. Frustrating! Wethus await the first confirmed dis-covery of an exoplanet with a massabout that of the Earth. (This dis-counts the two well-known objectsof a few Earth masses around thepulsar PSR 1257+12. These puzzlingobjects are sometimes ignored insurveys of exoplanets. Certainly,they are unlikely to be habitable.)Barrie W Jones, The Open University,Milton Keynes.
ReferenceBond I A et al. 2002 MNRAS 333 71.
Wilfried Schröder
Missing auroras and sunspots at the end of the 18th century
Date Auroras 1780 161781 33 1782 341783 331784 101785 151786 831787 761788 561789 561790 391791 141792 101793 11794 4 1795 0
1796 0 1797 0 1798 0 1799 1 1800 0 1801 0 1802 1 1803 3 1804 1 1805 2 1806 1 1807 0 1808 01809 01810 01811 01812 0
1813 01814 31815 01816 11817 71818 51819 101820 201821 241822 61823 01824 3 1825 51826 61827 181828 111829 18
Andrew Fraknoi
A new journal We are very pleased to announcecompletion of the first volume ofAstronomy Education Review, thenew on-line journal/magazine forastronomy and space-science educa-tion. The home page for the journalcan be found at aer.noao.edu. Weare now ready to receive contribu-tions for the first issue of volume 2.Astronomy Education Review aimsto serve a broad audience of thoseinvolved in education.
The journal welcomes submis-sions; guidelines are on the site.Sidney Wolff and Andrew Fraknoi,Editors; [email protected]
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