Keeping Time at Landis

By Geoff Miller

No gar­den is real­ly com­plete with­out a solar time­piece. Ear­ly sun­di­als were impor­tant tools for deter­min­ing plant­i­ng and har­vest dates, as well as pro­vid­ing time-of-day. The per­fect blend of sci­ence and art, sun­di­als con­nect us to the heav­ens in a quan­tifi­able way. 

The Lan­dis dial, promi­nent­ly installed on the front of the Barn, is a ver­ti­cal declin­ing dial, set to dis­play East­ern Day­light Time (March to Novem­ber). Dur­ing East­ern Stan­dard Time, sub­tract one hour from the dial read­ings. The Hour Lines’ are diag­o­nal lines radi­at­ing from a spot near the top of the dial. Lines cor­re­spond­ing to whole hours are sol­id, and half-hour lines are seg­ment­ed (to avoid con­fu­sion). Time is read where the shad­ow of the top edge of the gno­mon (called the style’) falls among the hour lines. 

This dial can be used to accu­rate­ly set one’s watch to with­in a minute or two, if one knows how to read it! To do so, read the dial and apply the Equa­tion of Time,’ a vari­able quan­ti­ty that needs to be added to (or sub­tract­ed from) the dial read­ing to obtain Mean Time.’ This is nec­es­sary because sun­di­als show Appar­ent Solar Time,’ while watch­es keep Mean Solar Time.’ The Equa­tion of Time’ (EOT) is sim­ply the dif­fer­ence between the two. An EOT plot is includ­ed in this arti­cle. It shows, for a giv­en date, the cor­rec­tion, in min­utes, to apply to the dial read­ing. If the EOT is neg­a­tive, that means the dial will be slow rel­a­tive to watch time and that the num­ber of min­utes must be ADDED to the dial read­ing. If the EOT is pos­i­tive, SUB­TRACT it from the dial reading.

In lieu of a 12:00 hour line, there is a funky fig­ure-eight curve on the dial that con­tains tick marks at the first day of each month. This is an analem­ma. It basi­cal­ly makes the EOT cor­rec­tion for you. When the cen­ter of the tip of the gno­mon’s shad­ow is exact­ly on the curve (between the appro­pri­ate month marks asso­ci­at­ed with the cur­rent date), it is pre­cise­ly 12:00 EDT (11:00 EST).

The two sweep­ing curved lines on the dial are sol­stice lines. On the win­ter sol­stice (ca. 1221) the tip of the gno­mon’s shad­ow will fol­low the upper curve through­out the day. The shad­ow tip will fol­low the low­er curve on the sum­mer sol­stice (ca. June 21). The diag­o­nal line that cuts through the mid­dle of the dial is the equinox or equinoc­tial’ line. On the equinox­es, when the Sun is in the equa­to­r­i­al plane, (ca. 320 and 921), the tip of the gno­mon’s shad­ow will fol­low that line.

Geoff Miller’s avo­ca­tion is gno­mon­ics,” the sci­ence of sun­di­als. A for­mer res­i­dent of the Cap­i­tal Dis­trict, he now lives in New Mex­i­co, return­ing to the area in the sum­mer. He ran in the Arboretum’s 5K race sev­er­al years ago and offered to con­struct a sun­di­al for Landis.

Spring 2022

Volume 40 , Number 1

Share this

The Latest from Landis

Mar 14, 2023

Picturing Landis through the year

Scenic Landis Arboretum just begs to be captured by photographers, professionals and amateurs alike. Enjoy... read more

Mar 14, 2023

2022 Annual Report

View or Download read more

Mar 14, 2023 | Nolan Marciniec

Re-thinking Garden Pests

“When we try to pick out anything by itself, we find it hitched to everything... read more

Mar 14, 2023 | Fred Lape, founder of the George Landis Arboretum

Barn Swallows

In this poem, Arboretum founder Fred Lape calls our attention to the “commonplace” miracle of... read more

Mar 14, 2023 | Anita Sanchez

Things Are Looking Up

Tree canopy -- Anita Sanchez Long ago I worked at a nature center, leading walks... read more

Mar 14, 2023 | Laurie Freeman

S-L-O-W Birding: A Primer for Beginners

Are you considering birding? Perhaps you’ve heard that birding is a great way to enjoy... read more

News Archive