VirginisR Documentation

John F. W. Herschel's Data on the Orbit of the Twin Stars γ Virginis

Description

In 1833 J. F. W. Herschel published two papers in the Memoirs of the Royal Astronomical Society detailing his investigations of calculating the orbits of twin stars from observations of their relative position angle and angular distance.

In the process, he invented the scatterplot, and the use of visual smoothing to obtain a reliable curve that surpassed the accuracy of individual observations (Friendly & Denis, 2005). His data on the recordings of the twin stars γ Virginis provide an accessible example of his methods.

Usage

	data("Virginis")
	data("Virginis.interp")

Format

Virgins: A data frame with 18 observations on the following 6 variables giving the measurements of position angle and angular distance between the central (brightest) star and its twin, recorded by various observers over more than 100 years.

year

year ("epoch") of the observation, a decimal numeric vector

posangle

recorded position angle between the two stars, a numeric vector

distance

separation distance between the two stars, a numeric vector

weight

a subjective weight attributed to the accuracy of this observation, a numeric vector

notes

Herschel's notes on this observation, a character vector

authority

A simplified version of the notes giving just the attribution of authority of the observation, a character vector

Virgins.interp: A data frame with 14 observations on the following 4 variables, giving the position angles and angular distance that Herschel interpolated from his smoothed curve.

year

year ("epoch") of the observation, a decimal numeric vector

posangle

recorded position angle between the two stars, a numeric vector

distance

separation distance, calculated 1/sqrt(velocity)

velocity

angular velocity, calcualted as the instantaneous slopes of tangents to the smoothed curve, a numeric vector

Details

The data in Virginis come from the table on p. 35 of the “Micrometrical Measures” paper.

The weight variable was assigned by the package author, reflecting Herschel's comments and for use in any weighted analysis.

In the notes and authority variables, "H" refers to William Herschel (John's farther, the discoverer of the planet Uranus), "h" refers to John Herschel himself, and "Sigma", rendered Σ in the table on p. 35 refers to Joseph Fraunhofer.

The data in Virginis.interp come from Table 1 on p. 190 of the supplementary paper.

Source

Herschel, J. F. W. III. Micrometrical Measures of 364 Double Stars with a 7-feet Equatorial Acromatic Telescope, taken at Slough, in the years 1828, 1829, and 1830 Memoirs of the Royal Astronomical Society, 1833, 5, 13-91.

Herschel, J. F. W. On the Investigation of the Orbits of Revolving Double Stars: Being a Supplement to a Paper Entitled "Micrometrical Measures of 364 Double Stars" Memoirs of the Royal Astronomical Society, 1833, 5, 171-222.

References

Friendly, M. & Denis, D. The early origins and development of the scatterplot. Journal of the History of the Behavioral Sciences, 2005, 41, 103-130.

Examples

data(Virginis)
data(Virginis.interp)

# Herschel's interpolated curve
plot(posangle ~ year, data=Virginis.interp, 
	pch=15, type="b", col="red", cex=0.8, lwd=2,
	xlim=c(1710,1840), ylim=c(80, 170),
	ylab="Position angle (deg.)", xlab="Year",
	cex.lab=1.5)

# The data points, and indication of their uncertainty
points(posangle ~ year, data=Virginis, pch=16)
points(posangle ~ year, data=Virginis, cex=weight/2)