Halley’s Comet | Calm Reading For Sleep

Drift off with this calm bedtime reading designed to ease you into sleep and soothe insomnia. In these gentle moments, you’ll explore the story of Halley’s Comet while settling into a peaceful state of rest. Unwind with a soft, steady narration as Benjamin guides you through the comet’s history, its predictable visits, and the science that makes it such a fascinating celestial traveler. You’ll discover something new while relaxing deeply, supported by his warm cadence—never whispered, just quiet, fact-filled comfort to ease stress, anxiety, and sleeplessness. Let your mind settle, your breath slow, and allow this serene reading to help you drift effortlessly toward rest. Happy sleeping!

Transcript

Welcome to the I Can't Sleep Podcast,

Where I help you drift off one fact at a time.

I'm your host,

Benjamin Boster,

And today's episode is about Halley's Comet.

Halley's Comet is the only known short-period comet that is consistently visible to the naked eye from Earth,

Appearing every 72 to 80 years,

Though with the majority of recorded apparitions occurring after 75 to 77 years.

It last appeared in the inner parts of the solar system in 1986,

And will next appear in mid-2061.

Officially designated 1P Halley,

It is also commonly called Comet Halley,

Or sometimes simply Halley.

Halley's periodic returns to the inner solar system have been observed and recorded by astronomers around the world since at least 240 BC.

But it was not until 1705 that the English astronomer Edmund Halley understood that these appearances were reappearances of the same comet.

As a result of this discovery,

The comet is named after Halley.

In March 1986,

During its latest visit to the inner solar system,

Halley's Comet became the first comet to be observed in detail by a spacecraft,

ESA's JOTO mission,

Providing the first observational data on the structure of a comet nucleus and the mechanism of coma and tail formation.

These observations supported several long-standing hypotheses about comet construction,

Particularly Fred Whipple's dirty snowball model,

Which correctly predicted that Halley would be composed of a mixture of volatile ices,

Such as water,

Carbon dioxide,

Ammonia,

And dust.

The missions also provided data that substantially reformed and reconfigured these ideas.

For instance,

It is now understood that the surface of Halley is largely composed of dusty,

Non-volatile materials,

And that only a small portion of it is icy.

It was also visited by the two spacecrafts of the Vega program,

Vega 1 and Vega 2,

On the 6th and 9th of March,

Respectively.

They went as close as 8,

890 km and 8,

030 km,

Providing data on Halley's dimensions,

Shape,

Temperature,

And surface properties.

Comet Halley is usually pronounced Hally,

Rhyming with Valley,

Or sometimes Haley,

Rhyming with Daily.

As to the surname Halley,

Colin Ronan,

One of Edmund Halley's biographers,

Preferred Hawley,

Rhyming with Crawley.

Spellings of Halley's name during his lifetime included H-A-I-L-E-Y,

H-A-L-E-Y,

H-A-Y-L-E-Y,

H-A-L-L-E-Y,

H-A-L-Y,

H-A-W-L-E-Y,

And H-A-W-L-Y.

So,

Its contemporary pronunciation is uncertain,

But the version rhyming with Valley seems to be preferred by modern bearers of the surname.

Halley was the first comet to be recognized as periodic.

Until the Renaissance,

The philosophical consensus on the nature of comets,

Promoted by Aristotle,

Was that they were disturbances in Earth's atmosphere.

This idea was disproven in 1577 by Tycho Brahe,

Who used parallax measurements to show that comets must lie beyond the Moon.

Many were still unconvinced that comets orbited the Sun,

And assumed instead that they must follow straight paths through the solar system.

In 1687,

Sir Isaac Newton published his Philosophiae Naturalis Principia Mathematica,

In which he outlined his laws of gravity and motion.

His work on comets was decidedly incomplete.

Although he had suspected that two comets that had appeared in succession in 1680 and 1681 were the same comet before and after passing behind the Sun,

He was later found to be correct.

He was initially unable to completely reconcile comets in his model.

Ultimately,

It was Newton's friend,

Editor and publisher Edmund Halley,

Who in his 1705 Synopsis of the Astronomy of Comets,

Used Newton's new laws to calculate the gravitational effects of Jupiter and Saturn on cometary orbits.

Having compiled a list of 24 comet observations,

He calculated that the orbital elements of a second comet that had appeared in 1682 were nearly the same as those of two comets that had appeared in 1531 and 1607.

Halley thus concluded that all three comets were the same object returning about every 76 years.

A period that has since been found to vary between 72 and 80 years.

After a rough estimate of the perturbations a comet would sustain from the gravitational attraction of the planets,

He predicted its return for 1758.

He personally observed the comet around Perihelion in September 1682,

But died in 1742 before he could observe its predicted return.

Halley's predictions of the comet's return proved to be correct,

Although it was not seen until the 25th of December,

1758,

By Johann Georg Paulitsch,

A German farmer and amateur astronomer.

Other observers from throughout Europe and its colonies sent confirmations to Paris after the comet brightened early the following year.

In the Americas,

John Winthrop lectured at Harvard University to explain the implications of the comet's reappearance for Newtonian mechanics and natural theology.

Another independent recognition that the comet had returned was made by Jamaican astronomer Francis Williams,

But his observations did not reach Europe.

A unique portrait commissioned by Williams demonstrates the impact of the comet's return on period astronomers.

Williams' hand rests on page 521 of the 3rd edition of Newton's Principia with procedures to predict comet sightings.

The white smudge in the sky is probably a depiction of Halley's comet relative to the constellations in March 1759,

And the cord hanging above the book likely represents the comet's orbit.

In 2024,

Using X-ray imaging,

The painting was shown to depict the field of stars in which the comet would have been visible in 1759.

Williams likely commissioned the portrait to commemorate his observations.

The comet did not pass through its perihelion until the 13th of March 1759,

The attraction of Jupiter and Saturn having caused a delay of 618 days.

This effect was computed before its return was a one-month error to the 13th of April by a team of three French mathematicians.

The confirmation of the comet's return was the first time anything other than planets had been shown to orbit the Sun.

It was also one of the earliest successful tests of Newtonian physics,

And a clear demonstration of its explanatory power.

The comet was first named in Halley's honor by French astronomer Nicolas-Louis Delacalle in 1759.

Some scholars have proposed that first-century Mesopotamian astronomers already had recognized Halley's comet as periodic.

This theory notes a passage in the Babylonian Talmud tractate Horeyot that refers to a star which appears once in 70 years that makes the captains of the ships Ur.

It has also been suggested that the passage may have referred to the variable star Mira,

Whose brightness oscillates with a period of 60 years.

Researchers in 1981 attempting to calculate the past orbits of Halley by numerical integration,

Starting from accurate observations in the 17th and 18th centuries,

Could not produce accurate results further back than 837,

Owing to a close approach to Earth in that year.

It was necessary to use ancient Chinese comet observations to constrain their calculations.

Halley's orbital period is varied between 74 and 80 years since 240 BC.

Its orbit around the Sun is highly elliptical,

With an orbital eccentricity of 0.

967,

With a zero being a circle and one being a parabolic trajectory.

The perihelion,

The point of the comet's orbit when it's nearest the Sun,

Is 0.

59 AU.

This is between the orbits of Mercury and Venus.

Its aphelion,

Or farthest distance from the Sun,

Is 35 AU,

Roughly the orbital distance of Pluto.

Unlike the overwhelming majority of objects in the solar system,

Halley's orbit is retrograde.

It orbits the Sun in the opposite direction to the planets,

Or clockwise from above the Sun's north pole.

The orbit is inclined by 18 degrees to the ecliptic,

With much of it lying south of the ecliptic.

This is usually represented as 162 degrees,

To account for Halley's retrograde orbit.

The 1910 passage was at a relative velocity of 70.

56 km per second.

Because its orbit comes close to Earth's in two places,

Halley is associated with two meteor showers.

The Eta Aquariids in early May,

And the Orionids in late October.

Halley is classified as a periodic or short-period comet.

One with an orbit lasting 200 years or less.

This contrasts it with long-period comets,

Whose orbits last for thousands of years.

Periodic comets have an average inclination to the ecliptic of only 10 degrees,

And an orbital period of just 6.

5 years.

So Halley's orbit is atypical.

Most short-period comets,

Those with orbital periods shorter than 20 years,

And inclinations of 30 degrees or less,

Are called Jupiter family comets.

Those resembling Halley with orbital periods of between 20 and 200 years,

And inclinations extending from 0 to more than 90 degrees,

Are called Halley-type comets.

As of 2024,

105 Halley-type comets have been observed,

Compared with 816 identified Jupiter family comets.

The orbits of the Halley-type comets suggest that they were originally long-period comets,

Whose orbits were perturbed by the gravity of giant planets,

And directed into the inner solar system.

If Halley was once a long-period comet,

It is likely to have originated in the Oort cloud,

A sphere of cometary bodies around 20,

000 to 50,

000 AU from the Sun.

Conversely,

The Jupiter family comets are generally believed to originate in the Kuiper belt,

A flat disk of icy debris between 30 AU and 50 AU from the Sun.

Another point of origin for the Halley-type comets was proposed in 2008,

When a trans-Neptunian object with a retrograde orbit similar to Halley's was discovered,

2008 KV42,

Whose orbit takes it from just outside that of Uranus to twice the distance of Pluto.

It may be a member of a new population of small solar system bodies that serves as the source of Halley-type comets.

Halley has probably been in its current orbit for 16,

000 to 200,

000 years,

Although it is not possible to numerically integrate its orbit for more than a few tens of apparitions,

And close approaches before 837 AD can only be verified from recorded observations.

The non-gravitational effects can be crucial.

As Halley approaches the Sun,

It expels jets of sublimating gas from its surface,

Which knock it very slightly off its orbital path.

These orbital changes cause delays in its perihelion passage of four days on average.

In 1989,

Boris Chirikov and Vytautas Vyacheslavov performed an analysis of 46 apparitions of Halley's comet,

Taken from historical records and computer simulations,

Which showed that its dynamics were chaotic and unpredictable on long timescales.

Halley's projected dynamical lifetime is estimated to be about 10 million years.

The dynamics of its orbit can be approximately described by a two-dimensional symplectic map,

Known as the Kepler map,

A solution to the restricted three-body problem for highly eccentric orbits.

Based on records from the 1910 apparition,

David Hughes calculated in 1985 that Halley's nucleus has been reduced in mass by 80-90% over the last 2,

000-3,

000 revolutions,

And that it will most likely disappear completely after another 2,

300 perihelion passages.

More recent work suggests that Halley will evaporate or split in two within the next few tens of thousands of years,

Or will be ejected from the solar system within a few hundred thousand years.

The Giotto and Vega missions gave planetary scientists their first view of Halley's surface and structure.

The nucleus is a conglomerate of ices and dust,

Often referred to as a dirty snowball.

Like all comets,

As Halley nears the sun,

Its volatile compounds,

Those with low boiling points,

Such as water,

Carbon monoxide,

Carbon dioxide,

And other ices,

Begin to sublimate from the surface.

This causes the comet to develop a coma,

Or atmosphere,

At distances up to 230,

000 km from the nucleus.

Sublimation of this dirty ice releases dust particles,

Which travel with the gas away from the nucleus.

Gas molecules in the coma absorb solar light and then re-radiate it at different wavelengths,

While dust particles scatter the solar light,

Making the coma visible.

As a fraction of the gas molecules in the coma are ionized by the solar ultraviolet radiation,

Pressure from the solar wind,

A stream of charged particles emitted by the sun,

Pulls the coma's ions out into a long tail,

Which may extend more than 100 million km into space.

Changes in the flow of the solar wind can cause disconnection events,

In which the tail completely breaks off from the nucleus.

Despite the vast size of its coma,

Halley's nucleus is relatively small,

Barely 15 km long,

8 km wide,

And perhaps 8 km thick.

Based on a re-analysis of images taken by the Giotto and Vega spacecraft,

Lamy et al.

Determined an effective diameter of 11 km.

Its shape has been variously compared to that of a peanut,

A potato,

Or an avocado.

Its mass is roughly 2.

2 x 1014 kg,

With an average density of about 0.

55 g per cubic cm.

The low density indicates that it is made of a large number of small pieces,

Held together very loosely,

Forming a structure known as a rubble pile.

Ground-based observations of coma brightness suggested that Halley's rotation period was about 7.

4 days.

Images taken by the various spacecraft,

Along with observations of the jets and shell,

Suggested a period of 52 hours.

Given the irregular shape of the nucleus,

Halley's rotation is likely to be complex.

The flyby images revealed an extremely varied topography with hills,

Mountains,

Ridges,

Depressions,

And at least one crater.

Halley's day side,

The side facing the sun,

Is far more active than the night side.

Spacecraft observations showed that the gases ejected from the nucleus were 80% water vapor,

17% carbon monoxide,

And 3-4% carbon dioxide,

With traces of hydrocarbons.

Although more recent sources give a value of 10% for carbon monoxide,

And also include traces of methane and ammonia.

The dust particles were found to be primarily a mixture of carbon,

Hydrogen,

Oxygen,

Nitrogen compounds,

Common in the outer solar system,

And silicates,

Such as are found in terrestrial rocks.

The dust particles ranged in size down to the limits of detection.

The ratio of deuterium to hydrogen in the water released by Halley was initially thought to be similar to that found in Earth's ocean water,

Suggesting that Halley-type comets may have delivered water to Earth in the distant past.

Subsequent observations showed Halley's deuterium ratio to be far higher than that found in Earth's oceans,

Making such comets unlikely sources for Earth's water.

Giotto provided the first evidence in support of Fred Whipple's dirty snowball hypothesis for comet construction.

Whipple postulated that comets are icy objects warmed by the sun as they approach the inner solar system,

Causing ices on their surfaces to sublime,

Change directly from a solid to a gas,

And jets of volatile material to burst outward,

Creating the coma.

Giotto showed that this model was broadly correct,

Though with modifications.

Halley's albedo,

For instance,

Is about 0.

04,

Meaning that it reflects only 4% of the sunlight hitting it,

About what one would expect for coal.

Thus,

Despite astronomers predicting that Halley would have an albedo of about 0.

17,

Roughly equivalent to bare soil,

Halley's comet is,

In fact,

Pitch black.

The dirty ices on the surface sublime at temperatures between 170 Kelvin in sections of higher albedo to 220 Kelvin at low albedo.

Vega 1 found Halley's surface temperature to be in the range 300 to 400 Kelvin.

This suggested that only 10% of Halley's surface was active,

And that large portions of it were coated in a layer of dark dust that retained heat.

Together,

These observations suggested that Halley was,

In fact,

Predominantly composed of non-volatile materials,

And thus more closely resembled a snowy dirtball than a dirty snowball.

Due to its intrinsic brightness,

About one-eighth of all comet sightings mentioned in historic records belong to Halley's comet.

The first certain appearance of Halley's comet in the historical record is a description from 240 BC in the Chinese Chronicle Records of the Grand Historian,

Or Shiji,

Which describes a comet that appeared in the east and moved north.

The only surviving record of the 164 BC apparition is found on two fragmentary Babylonian tablets,

Which were rediscovered in August 1984 in the collection of the British Museum.

The apparition of 87 BC was recorded in Babylonian tablets,

Which state that the comet was seen day by day for a month.

This appearance may be recalled in the representation of Tigranes the Great,

An Armenian king who is depicted on coins with a crown that features,

According to Vahe-Gurzadyan and R.

Vardanyan,

A star with a curved tail that may represent the passage of Halley's comet in 87 BC.

Gurzadyan and Vardanyan argue that Tigranes could have seen Halley's comet when it passed closest to the sun on August 6th in 87 BC,

As the comet would have been a most recordable event.

The apparition of 12 BC was recorded in the Book of Han by Chinese astronomers of the Han Dynasty,

Who tracked it from August through October.

It passed within 0.

16 astronomical units of Earth.

According to the Roman historian Cassius Dio,

A comet appeared suspended over Rome for several days,

Portending the death of Marcus Vipsanius Agrippa in that year.

Halley's appearance in 12 BC,

Only a few years distant from the conventionally assigned date of the birth of Jesus Christ,

Has led some theologians and astronomers to suggest that it might explain the biblical story of the Star of Bethlehem.

There are other explanations for the phenomenon,

Such as planetary conjunctions,

And there are also records of other comets that appeared closer to the date of Jesus' birth.

If Yehoshua ben Hananiah's reference in the Talmud to a star which arises once in 70 years and misleads the sailors refers to Halley's comet,

He can only have witnessed the 66 AD appearance.

Another possible reference to the same apparition is also found in the writings of the Jewish historian Josephus,

Who described several portents visible over Jerusalem shortly before the outbreak of the First Jewish-Roman War.

He reported that there was a star resembling a sword,

Which stood over the city,

And a comet that continued a whole year,

Events that were interpreted as omens of the city's destruction in 70 AD.

The 141 AD apparition was recorded in Chinese chronicles as observations of a bluish-white comet on 27th and 16th of March,

22nd of April,

And 23rd.

The early Tamil bards of southern India also describe a certain relatable event.

The 374 AD and 607 approaches each came with 0.

09 astronomical units of Earth.

The 451 AD apparition was said to herald the defeat of Attila the Hun at the Battle of Shallins.

The 684 AD apparition was reported in Chinese records as the Broom Star.

The 760 AD apparition was recorded in the Züchnin Chronicles entry for Eeyore 1071 SE,

May 760 AD,

Calling it a white sign.

The year SE 1071,

In the month of Eeyore,

May,

A white sign was seen in the sky before early twilight,

In the northeast quarter,

In the zodiac sign,

Which is called Aries,

To the north from these three stars in it,

Which are very shining.

And it resembled in its shape a broom.

And the sign itself remained for 15 nights until dawn of the Feast of Pentecost.

In 837 AD Halley's comet may have passed as close as 0.

03 astronomical units from Earth,

By far its closest approach.

Its tail may have stretched 60 degrees across the sky.

It was recorded by astronomers in China,

Japan,

Germany,

The Byzantine Empire,

And the Middle East.

Emperor Louis the Pious observed this appearance and devoted himself to prayer and penance,

Fearing that by this token a change in the realm and the death of a prince are made known.

In 912 AD Halley is recorded in the Annals of Ulster,

Which states,

A dark and rainy year,

A comet appeared.

Thanks for watching!

Reviews

I remember Hally's comet. It was a very exciting occurrence in my young life. If I keep getting good rest, I may yet see it again!

Enjoyed this one Benjamin. I missed seeing it in 86. Too bad. I’ll be long dead when it comes into view again!! But Thank you anyway !!