New Scientist - USA (2022-04-16)

16 April 2022 | New Scientist | 9

WE MAY have figured out the
date from which an ancient
device often described as the first
computer began its calculations.
This device, called the Antikythera
mechanism, was built sometime
between the years 200 BC and
60 BC, and it was used to track
time and predict the motions
of celestial bodies.
A spiral shape inset in the
back of the mechanism depicts
a 223-month cycle called a Saros,
which is based on the amount
of time it takes for the sun, moon
and Earth to return to the same
relative positions and repeat a
cycle of similarly timed solar
and lunar eclipses.
Aristeidis Voulgaris at the
Thessaloniki Directorate of
Culture and Tourism in Greece
and his colleagues used this to
calculate a sort of starting date
for the Antikythera mechanism,
the “Day Zero” by which its
calculations were calibrated.
“Any measuring system,
from a thermometer to the
Antikythera mechanism, needs
a calibration in order to [perform]
its calculations correctly,” says

Voulgaris. “Of course, it wouldn’t

have been perfect – it’s not a digital

computer, it’s gears – but it would

have been very good at predicting

solar and lunar eclipses.”

Based on our understanding

of how the mechanism works

and the inscriptions on it, the

calibration date was expected to

occur during a particular kind of

solar eclipse in which the moon

was located at the furthest spot

in its orbit from Earth, a position

called apogee. Voulgaris and his

colleagues searched a NASA

repository of eclipse calculations

for unusually long-lasting eclipses,

which occur when the moon is

particularly far from Earth.

The longest such eclipse during

the era when the Antikythera

mechanism was built occurred

in the small hours of 23 December

178 BC. When they looked further

into this date, the researchers

found that several astronomical

events of cultural significance

occurred then, including the

winter solstice, which is engraved

at the top left of the front of the

mechanism, which Voulgaris

says is a hint at its importance

to calibration (arxiv.org/

abs/2203.15045).

“This is a very specific and

unique date,” says Voulgaris.

“In one day, there occurred too

many astronomical events for

it to be coincidence – this date

was a new moon, the new moon

was at apogee, there was a solar

eclipse, the sun entered into

the constellation Capricorn,

it was the winter solstice.”

However, other prominent

researchers in the field have

found a different calibration date.

“The eclipse predictions on

the [device’s back] contain enough

astronomical information to

demonstrate conclusively that

the 18-year series of lunar and

solar eclipse predictions started

in 204 BC,” says Alexander Jones

at New York University. There

have been four independent

calculations of this, he says. “The

reason such a dating is possible is

because the Saros period is not a

highly accurate equation of lunar

and solar periodicities, so every

time you push forward by 223

lunar months... the quality of

the prediction degrades.”

These other works relied on

finding the one Saros period

for which the mechanism’s

astronomical predictions

would have been most accurate.

However, the date that they found

is in the summer, which would

leave the question of why the

winter solstice engraving is so

prominent on the Antikythera

mechanism’s front plate

unanswered, says Voulgaris. ❚

Astronomy

Leah Crane

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Ancient computer may have had its

clock set to 23 December 178 BC

The Antikythera

mechanism, built at

least 2080 years ago

Cosmology

A GALAXY called HD1 may be the
most distant object ever seen. Its
astonishing brightness could be due
to a huge black hole or the creation
of extremely massive primordial
stars, both of which confound our
understanding of the early universe.
Fabio Pacucci at the Harvard-
Smithsonian Center for Astrophysics
in Massachusetts and his colleagues
found HD1 by sifting through data
from several of the most powerful

telescopes available. Next, they

observed it with the Atacama Large

Millimeter/submillimeter Array in

Chile. They found that HD1 is about

33.4 billion light years away, more

than a billion light years further

than the previous most distant

object ever spotted. This is possible,

despite the universe being only

about 13.8 billion years old,

because of the accelerating

expansion of the cosmos.

HD1 is extraordinarily bright in

ultraviolet wavelengths, meaning

that whatever is producing its light

is probably extremely hot. There

are two possibilities: it hosts a burst

of star formation much bigger than

we would expect for the galaxy’s

relatively small size or it is home

to an active supermassive black

hole (Monthly Notices of the Royal

Astronomical Society, doi.org/hpps).

If it is a starburst, HD1 would have

to be producing about 110 times the

sun’s mass in stars every year. “It’s

a crazy number,” says Pacucci. “One

explanation is this galaxy might

not be forming normal stars, but

these primordial stars that are much

more massive and much hotter than

normal nearby stars.” We have never

seen such primordial stars before.

Or it could host an unexpectedly

colossal supermassive black hole.

“The observation of a 100-million-

solar-mass black hole so early in the

history of the universe would really

be groundbreaking, because we

really wouldn’t be sure how to form

this,” says Pacucci. We are seeing

HD1 as it was just 330 million

years after the big bang, and it

is unclear how a black hole could

have become so big so quickly. ❚

Astronomers have

spotted the most

distant galaxy ever

Leah Crane

33.

Distance in billions of light years

to the HD1 galaxy