Huh? Nope, it’s Heh: How the Egyptians measured time and thought about eternity

The week is finally over! While only five days long, the workweek can certainly feel like an eternity. Which got me thinking (as many things do) about how the Egyptians measured time and thought about eternity.

Houston HehBarely an inch in height, this small hammered gold object depicts a man kneeling, wearing a knee-length pleated linen kilt and a long wig which comes down in two lappets on either side of his face – the typical get-up of Egyptian gods. His right hand stretches out to grasp a tall element with a curving top; his missing left hand originally did the same.

His pose and accessories identify him as the god Heh. Larger, more detailed representations show that the curved objects he holds are palm ribs, notched to tally up the years. The ‘years’ often rest on crouching frogs or tadpoles, the hieroglyphic sign for ‘100,000;’ these in turn sit on top of tied rings, symbolizing enduring protection.

Big HehWith all this in mind, it’s no surprise that Heh was considered the god of eternity, and was himself used as the hieroglyphic sign for ‘1,000,000’ – the largest number the Egyptians wished to write. Images of Heh in temples and on royal objects provided an eternal framework for the rituals that surrounded them. Tutankhamun was buried with a mirror in a Heh-shaped case, keeping him forever safe and youthful.

Our Heh is smaller and less finely worked than these, but is still made from expensive gold and would have been a cherished possession of its owner. A loop soldered to his back allowed him to be attached to a cord, where he would have served as an amuletic charm on a necklace, or possibly an element of a diadem.

Excavated parallels to our Heh date to the late Old Kingdom and First Intermediate Period (which we Egyptologists abbreviate to ‘FIP’) of Egyptian history (Dynasties 6-10, around 2300-2000 BC), and illuminate the problems we can run into when studying the past. Literary accounts of the First Intermediate Period describe it as a period in which the legitimate king was unable to exercise his authority: chaos, fighting, and famine ensued until the kings of the Middle Kingdom were able to reunite the country.

Excavations of FIP cemeteries, however, reveal a different picture. Valuable metal objects like weapons and our Heh are preserved in far higher quantities from FIP graves than Old Kingdom graves. If the FIP didn’t benefit the king and his court, less privileged people used the weakening of royal control as an opportunity to enrich themselves in this life and the next.

The amulet of Heh will go on display in the Hall of Ancient Egypt in the summer. Keep an eye out for him!

How to Use the HMNS Sundial

At 6:45 am on Friday, March 20, 2009, the Sun is overhead at the equator, marking the vernal (spring) equinox.  Here at the Museum, we’ll mark the occasion with Sun-Earth Day, one of the Fun Hundred events marking our 100th anniversary.  As part of these festivities, I will be on the Cockrell Sundial from 1 to 1:45pm, showing everyone the Sun and how to use our sundial.  Whether or not you’re able to join me on Friday, the following guide to the sundial will help you get more out of this large scientific exhibit which is free to the public.

The main features of any sundial, including ours, are the hour lines.  These are dark lines marked with roman numerals indicating the hour.  The object which casts the shadows you use to read the time on a sundial is the gnomon.  Our gnomon is especially designed for our location; the angle it makes with the base of the sundial is 29.72o, the precise latitude of the Houston Museum of Natural Science.  When the Sun shines on the gnomon, the location of its shadow on the sundial indicates the time of day.  We don’t mark fractions of the hour (as most sundials don’t), so if you’re not observing on the hour, you’ll need to interpolate a bit and estimate the time.  Further, our sundial can’t ‘spring forward’, so the time you read will be about an hour behind until Daylight Saving Time ends in November. 


Along with the hour lines, we have added some features which serve to make our sundial more accurate then most and to teach visitors a little more about how we tell time. 

You might notice, for example, that there is a brown line that points at due north, and that the noon line is offset from this.  That’s because the time on your watch, iPod, or cell phone is local time not in Houston, but in New Orleans.  Earth completes one rotation (does a ‘360’) in 24 hours.  Therefore, Earth rotates by 360/24 = 15 degrees in one hour.  When people around the world decided to create standard time zones, these zones were defined based on longitudes 15 degrees apart.  Time zones in the United States are based on 75oW (Eastern Time), 90oW (Central Time), 105oW (Mountain Time), 120oW (Pacific Time), 135oW (Alaska Time), and 150oW (Hawai’i Time).  As a result, when your timepiece reads Central Time, it reads the time at 90oW, the longitude of New Orleans, Memphis, and East St. Louis, IL.  In any of these places, the noon line on a sundial would be exactly aligned with due north.  Houston, however, is at just over 95oW.  We have offset the noon line from true north to compsensate for this. 

Along the noon line, you’ll also notice small, shiny circles in the shape of an elongated figure 8.  This is the analemma.  Earth’s orbit around the Sun is an ellipse, not really a circle.  Instead of remaining at a constant distance from the Sun, Earth has a perihelion (in January) when it is slightly closer to the Sun, and an aphelion (in July), when it is slightly father away.  The difference is small, but enough to make Earth speed up near perihelion and slow down near aphelion.  This in turn causes the Sun to be a little ahead or lag a bit behind mean solar noon.  The difference between mean solar noon and the actual solar noon on a given date is the equation of time.  If you plotted the Sun’s position in the sky at precisely the same time of day throughout a year, you would create an elongated figure 8: this is the analemma.  This is the figure we have reproduced on the sundial.  At noon (or 1pm in Daylight Saving Time), the gnomon’s shadow will fall not on the noon line, but on the analemma.  Note the difference between the analemma point and the noon line on the date of your visit; you’ll need to mentally adjust the shadow’s position by that much to make it agree with your timepiece. 

The months of the year are also indicated along the noon line.  December is indicated farthest from the gnomon, then January/November, February/October, March/September, April/August, May/July, and June.  The month names are written in a way to help you use the analemma.   In each pair, the month on ‘top’  (farther from the gnomon) is a month when the Sun is slightly behind mean solar noon and the shadow falls on the analemma to the left of the noon line (as you face north).  During the months on the ‘bottom’ of each pair (closer to the gnomon), the Sun is slightly ahead of mean solar noon, and the noon shadow lands on the analemma to the right of the noon line.   Silver curves associated with each month or pair of months show the path of the gnomon’s shadow on about the 21st of each month.  At a glance, you can see how much longer the shadow is in December, when the Sun is low, than in June, when the Sun is almost overhead. 

img_0012On top of the gnomon is a silver ball with three pairs of holes.  These holes are aligned such that the Sun shines through a pair of holes near the equinoxes and solstices (in 2009: March 20, June 21, September 22, and December 21).  To allow for cloudy weather, the holes are big enough for the Sun to shine through them for several days on either side of the equinox or solstice date.  (The holes aligned with the winter solstice are especially large, such that the Sun shines through them for over a month before and after December 21).  In each set of holes are lenses which focus sunlight, so you can project a real image of the Sun on a sheet of paper.  This works only when the Sun is close to due south–the 1:00 hour during Daylight Saving Time.  If you see a bright circle of light inside the rounded top end of the shadow–the shadow of the silver ball on top of the gnomon–it’s close enough to the equinox (or solstice) to project the Sun.  Place a sheet of paper in the light path, lift or lower the paper to focus, and voila!  A live image of the Sun is in your hands.  If any sunspots are present, they’ll show up in your image.   As I write this, there are no sunspots on the Sun, which astronomers find somewhat baffling.  Here is where you can see how many sunspots there are on the day you come.

Of the four solstice and equinox dates, June and September are usually oppressively hot and December is often cloudy.  That leaves the spring equinox, March 20, which has comfortable temperatures and a reasonable chance of clear skies.  That’s why we have chosen this date for our Sun-Earth Day.

If you like our sundial, you can take one home with you!  Well, this offer is only for Friday’s Sun-Earth Day event, and the one you make won’t have all the bells and whistles on ours.  You’ll still go home with you very own hand made timepiece.  Other activities include solar cooking and etching your initials into a popsicle stick with a Fresnel lens (yes, that’s why you don’t want to look directly at the Sun). 

Come on out and join us on Friday!

What the Heck is a Tues, Wed, Thurs, or Fri?

Earth Mars and Moon to scale
Creative Commons License photo credit: Bluedharma

We measure time based on motions in space.  The Earth rotates on its axis once a day.  The Moon orbits the Earth about once a month.  The Earth orbits the Sun once a year.  That leaves the week as the only aspect of our calendar not directly tied to the Earth, Moon, or Sun. The week, as it turns out, is based on the other planets of our solar system–at least, those easily visible to the naked eye.

Early astronomers were able to distinguish planets from stars because planets seem to move against the starry background.  The stars are always rising, moving across the sky, and setting due to Earth’s rotation.  They seem to form the same patterns all the time; we never see them move relative to each other.  (In fact the stars do have proper motion, but we don’t notice it over a time frame as short as a human life or even over several generations).  Anything shifting noticeably over several days was a ‘wandering star’, or planet.  Early astronomers identified seven ‘wanderers’: the Moon, Mercury, Venus, the Sun, Mars, Jupiter, and Saturn, and the Greeks placed them in just that order.

This order, of course, is wrong; it makes the basic error of putting the Sun in orbit around the Earth when in fact the Earth orbits the Sun.  Fixing this error by replacing the Sun with the Earth, however, makes the order from Mercury to Saturn correct.  That’s because the order is based on something directly observable–the planets seem to move among the background stars at different rates.  Ancient observers saw the Moon reappear near the same set of stars once a month.  Saturn, on the other hand, takes 29.5 years to reappear in the same part of the sky. 

The different speeds are even more apparent when two or more planets are near one another in the sky (an alignment called conjunction).  Any planet in conjunction with Saturn catches up to Saturn and then passes it.  It’s never the other way around.  Any planet (other than Saturn) in conjunction with Jupiter catches and passes Jupiter, never the other way around.  For early astronomers, slowness was associated with distance.  By carefully observing the planets’ motions and planetary conjunctions, early observers could place them in order.

Ancient Roman writer Dio Cassius was among the first to explain how the order of the planets from slowest to fastest (and thus from outside in) generated the week.  The system involves the 24-hour day and an astrological belief that each hour was ‘ruled’ by a planet following the order above, such that Saturn’s hour was followed by Jupiter’s, then Mars’, then the Sun’s, and so on.  Further, whichever planet governed the first hour of each day governed that whole day.  On Saturn’s day, then, the hours were as follows:

1) Saturn  2) Jupiter  3) Mars  4) Sun  5) Venus  6) Mercury  7) Moon 8. Saturn  9) Jupiter  10) Mars  11) Sun  12) Venus  13) Mercury  14) Moon  15) Saturn  16) Jupiter  17) Mars  18) Sun  19) Venus  20) Mercury  21) Moon  22) Saturn  23) Jupiter  24) Mars  25) Sun

Since there are 24 hours in a day, the 25th hour of Saturn’s day is the first hour of the next day.  Therefore, Saturn-day is followed by Sun-day.  Redo the list of hours, this time starting with the Sun, such that hours 1, 8, 15, and 22 are the Sun’s.  Hour 25 becomes the Moon’s hour, which means the Sun-day is followed by Moon-day.  Repeat the list with the Moon in first position, and eventually the following order of days emerges:

1) Saturn-day  2) Sun-day  3) Moon-day  4) Mars-day  5) Mercury-day  6) Jupiter day  7) Venus-day

If Venus governs the first hour, Saturn governs the 25th, and the cycle begins again.  A full table of the hours and days is here (this list also has the name of the days in 30 different languages).

You probably recognize Saturday, Sunday, and Monday in this list.  To get the other English day names from this list, we have to translate by replacing the planet names, which are names of Roman deities, with roughly equivalent Germanic deities.  Languages derived directly from Latin have preserved the Roman gods’ (thus the planets’) names more faithfully.  For example, you can recognize Latin luna (the Moon) in French lundi, Spanish lunes, and Italian lunedì.

Apollo Belvedere
Creative Commons License photo credit: Alun Salt

Similarly, Mars-day is martes in Spanish, mardi in french, and martedì in Italian.  Germanic tribes, however, replaced the Roman war god Mars with their own warlike god Tiw (or Tyr for the Norse).  Thus, Mars’ day became Tiw’s day or Tuesday.

‘Mercury-day’ is recognizable in French mercredi, Spanish miércoles, and Italian mercoledì.  The Germanic pantheon had no messenger god that corresponded well to the Roman Mercury, so they equated him with Woden (Norse Odin).  Both Woden and Mercury were gods who escorted the recently deceased to the underworld.  Also, Woden became the fastest god when he rode his eight-legged horse Sleipnir.

Creative Commons License photo credit: Pro-Zak

Jupiter’s original name in Latin was Jovis (‘Jove’ to English writers); the name Jupiter is a contraction of Jovis pater (‘father Jove’).  ‘Jove-day’ is recognizable in French jeudi, Spanish jueves, and Italian giovedì.   Although Jupiter, like the Greek Zeus, was the king of all the gods, his actual domain was the weather.  In particular, he was the god who caused storms and struck people with lightning.  Thus Germanic tribes assigned his day to Thor, their god of thunder.  Thor’s day is Thursday.

‘Venus-day’ is still recognizeable in French vendredi, Spanish viernes, and Italian venerdì.  Germanic tribes replaced Venus’s name with that of Frigg, the wife of Woden who was associated with married women and whom they called upon to help in giving birth.  Frigg-day is Friday.

As the Germanic tribes had no one in their pantheon who even roughly corresponded to Saturn, Saturn’s name remains in Saturday.  Ironically, the Latin-based languages have lost ‘Saturn-day’ as the day’s name.  Spanish sábado and Italian sabato derive from the word ‘sabbath’ (as does French samedi, through a more complex etymology).  This is due to the influence of the Catholic Church, which was loath to name the days of the week after pagan gods, and sought to replace the planetary names. 

The Church designated Sunday ‘Lord’s Day’ (dies dominicus), called Saturday the sabbath (sabbatum), and numbered the weekdays from 2 to 6.  Except in Portugal, however, the numbered weekdays never replaced the planetary days in popular usage.  Everyday people in southern Europe did adopt the Church’s terms for the weekend days.  Northern Europe, largely outside the influence of the Catholic Church, was less affected by this; we retain ‘Saturday’ and ‘Sunday’ in English as a result.

In November and December 2008, you can make for yourself some of the observations that helped astronomers of antiquity imagine the solar system.  The two brightest points of light in the southwest tonight are Venus and Jupiter.  They outshine all stars we ever see at night and are visible even in twilight.  But don’t wait too late; you’ll need to look in the hours right after sundown before the two planets set.  Venus, lower to the horizon, is the brighter of the two.  Its closeness to us and the clouds that cover the whole surface and reflect most sunlight back into space cause Venus to outshine the much larger Jupiter.

Watch as Venus gets closer and closer to Jupiter each night this month.  This is exactly how ancient astronomers could tell that Venus and Jupiter were not stars.  On November 30 and December 1, watch as Venus passes 2 degrees ‘under’ Jupiter.  (The crescent Moon also passes by on these nights).  Imagine ancient Greek astronomers concluding that Venus is closer because it is faster.  Keep watching each night in December as Venus pulls away from Jupiter, getting higher in the dusk sky while Jupiter sinks into the Sun’s glare by early January.  Early astronomers would have seen this as the Sun catching up to Jupiter while Venus pulls away; observations like this account for the Sun’s position in the ancient order of ‘planets’.  Of course, we now know better–the Sun’s apparent motion is really ours.  Earth is going around the far side of the Sun from Jupiter’s position, putting Jupiter behind the Sun as the New Year opens. 

Venus remains an evening star until March 2009.  Compare Venus to the stars around it, and you’ll see it slow down and then move ‘backwards’ towards the Sun’s position each night in March.  That’s because Venus will have come around to our side of the Sun, and will be passing us up on its faster orbit. 

Should you make any of these observations on a Thursday or Friday, you can reflect on why those days have those names.