A Pedestal of the Sun for the Solstice

Analemma printed on a globe (Globe Museum, Vienna)

The second solstice for the year is today, December 21st. It literally happens at a moment in time but like many cosmic events, most of us think of it as a day. For those in Northern Hemisphere, it will be the winter solstice and for those in Southern Hemisphere, it will be the summer solstice marking the first day of the two seasons.

At that moment, it will be sunset in North and South America, sunrise in far-eastern Asia, midnight in Africa and Europe, and noontime over the Pacific Ocean.

In Paradelle (Northern Hemisphere), we will have our shortest day and longest night of the year. This month, one rotation of Earth relative to the noonday sun – what we call a day – is about 30 seconds longer than the average 24 hours. Get past that “day” that is on your calendar or the idea of that clock face.

You would actually be better off measuring the true length of a solar day (the time from one solar noon to the next) by using a sundial.

The photo at the top of this post shows an analemma printed on a globe that shows the sun’s declination. That is the angular distance from the celestial equator and the difference (in minutes) between time as measured by the clock and time as measured by the sun. Sounds complicated, right?

In fact, in astronomy, an analemma (from Greek “pedestal of a sundial”) is a curve representing the changing angular offset of a celestial body (usually the Sun) from its mean position on the celestial sphere as viewed from another celestial body (usually the Earth).  Still complicated.

Analemma plotted as seen at noon GMT from the Royal Observatory, Greenwich (latitude 51.48° north, longitude 0.0015° west).

The Earth’s annual revolution around the Sun is an elliptical orbit. That means it is tilted relative to the plane of the equator. We, being observers at a fixed point on the Earth, see the Sun appear to move in an analemma around a mean position. If you observed the position of the Sun in the sky and plotted it or photographed it at the same time every few days, all year-long, the points would trace out the analemma.

I did this very unscientifically one year by just noting where the Sun appeared (I used a compass) when viewed every morning as I had my breakfast and gazed out the east window. It amazed me how far the Sun moved during the year. I ended up with a graph of the Sun’s declination plotted against the equation of time.

Like the “equator” or other terms, an analemma is an abstract concept. It has no physical existence except in diagrams and time-lapse photographs. Nevertheless, we do describe it as if it were a real, visible celestial object.

This afternoon analemma photo was taken in Murray Hill, NJ – not far from Paradelle – at Bell Laboratories where my father worked in the 1950s and early 196os.

Autumn Comes But Twice a Year

Image by pasja1000 from Pixabay

I suspect your calendar says autumn will arrive on September 22, but it arrived on the first of September along with some violent weather that arrived in Paradelle.

By the meteorological calendar, the first day of autumn is always  September 1 and the season ends November 30. The meteorological calendar defines the season quite cleanly as spring (March, April, May), summer (June, July, August), autumn (September, October, November) and winter (December, January, February).

Most of us were taught that the seasons change with solstices and equinoxes.  Those are the astronomical seasons that follow the position of Earth in relation to the sun. Meteorological seasons follow the annual temperature cycle and match our Gregorian calendar.

The dates of the Equinox and Solstice aren’t fixed due to the Earth’s elliptical orbit of the Sun. The Earth’s orbit around the Sun is closest (perihelion) in early January. In early July,  it is most distant (aphelion). That always seems odd to people. Closer is not warmer. Farther is not colder.

On the autumn equinox, day and night are of roughly equal length. Nights become increasingly longer than the days – something you are no doubt are already observing. The pattern reverse with the spring equinox.

So, when is it really the start of autumn? For those of us living on the top half of the Earth, I say it is with the autumn equinox when the northern hemisphere begins to tilt away from the Sun. That means less direct sunlight hits us so temperatures cool.

The end of summer in September – and hopefully early October – is one of my favorite times of the year.  In some years and in some places in the north, we may get what has become known as “Indian Summer” – that imaginary season that occurs when temperatures are more summer than autumn from late September to mid-November.

I love it when summer gets a second chance. Sometimes the universe doesn’t play by the rules of meteorology and astronomers.

That Dialogue on Opposing World Systems

Galileo and Copernicus    (Gilgub/Flickr)

The title “Dialogue Concerning the Two Chief World Systems” certainly sounds like a heavy topic. It was heavy in 1632 when Galileo published it. The two systems were the Ptolemaic and the Copernican theories of cosmology. It is less controversial and easier to understand today.

Ptolemy, following the tradition of Aristotle, believed that the Earth was the center of the universe, and everything — Sun, Moon, planets, and stars — revolved around it.

Copernicus, on the other hand, posited that the Sun is the center of the universe, and though we seem to be standing still, we are in fact hurtling through space as we circle the star.

I used to have a quotation in my middle school classroom for my students that said “You are not the center of the universe” – Copernicus. Nicholas didn’t say exactly that quote, and he wasn’t specifically referencing my young teen students, but it was a good point-of-departure quote for discussion.

Galileo had spoken with Pope Urban VIII earlier and discussed his tide theory as proof that the Earth moved through space – not that the Sun was the center of the universe. The Pope granted him permission to write “Dialogue on the Tides” but that the Copernican theory should be treated as hypothetical in the book. Wisely, Galileo wrote the book as a series of discussions between two philosophers. One believed in Copernicus, one believed in Ptolemy, and a neutral but well-educated layman served as a moderator. That got it past the Catholic censors.

But Galileo was Copernican all the way and the popular book did not please Pope Urban VIII who had Galileo tried by the Inquisition. They ruled that he was “vehemently suspect of heresy” and too close to endorsing Copernican theory and the book was placed on the Catholic Church’s Index of Forbidden Books.

Galileo was ordered to recant and recite weekly psalms of penitence. He spent the rest of his life under house arrest, and none of his later books were permitted to be published in his lifetime.

The Dialogue on Opposing World Systems remained on the Index of Forbidden Books until 1835. Change is slow in religion – but not in science.

Further Reading

The Essential Galileo

Earth Had a New Moon

I’m not writing here about the monthly New Moon phase that will appear this Sunday. I’m talking about a news item that didn’t get a lot of attention.

It seems that Earth acquired a second “mini-moon.” It’s not very big – about the size of a small car. Astronomers spotted it circling our planet back in February.

Researchers Kacper Wierzchos and Teddy Pruyne at the NASA-funded Catalina Sky Survey in Arizona. They say that Earth has “temporarily captured” this object which is a “possible mini-moon called 2020 CD3,” and likely to be a C-type asteroid.

Any Near-Earth Object (NEO) that follows an Earth-like orbit may eventually be captured by Earth’s gravity during low-velocity encounters. This is just the second asteroid known to orbit Earth (2006 RH120 was first). Its route suggests it entered Earth’s orbit three years ago.

Okay, it doesn’t look so impressive in this International Gemini Observatory image. This is 2020 CD3.

The Smithsonian Astrophysical Observatory’s Minor Planet Center collects data on minor planets and asteroids says it is likely an asteroid captured by Earth’s gravity.

Our “new moon” is not in a stable orbit around us and so it didn’t stay long enough to get really established in our imagination. I don’t imagine there will be many poems written about it. (What rhymes smoothly with 2020 CD3?) It orbited Earth like a tiny natural satellite. It seems like Asteroid 2020 CD3 has now gone back into orbit around the sun, so it is tailing us on our annual journey around the Sun after about a year of travel around Earth.

Farewell, 2020 CD3. Have a good journey.

The Heartbeat of the Planet

Checking a person’s pulse is a way to know that the person is alive or how fast their heart is beating. A normal resting heart rate for adults ranges from 60 to 100 beats per minute. Generally, a lower heart rate at rest implies more efficient heart function and better cardiovascular fitness. For example, a well-trained athlete might have a normal resting heart rate closer to 40 beats per minute.

Every 26 seconds, the Earth pulses.

The Earth’s pulse is not enough that you can feel it. Seismologists in different places around the world have been measuring the pulses for decades, but they don’t know for sure what is causing it.  This pulse was first documented in the early 1960s.

In seismology, the term microseism is defined as a faint earth tremor caused by natural phenomena and it is sometimes referred to as a “hum.” According to Wikipedia, it should not be confused with the anomalous acoustic phenomenon of the same name. The term is most commonly used to refer to the dominant background seismic and electromagnetic noise signals on Earth, which are caused by water waves in the oceans and lakes.

Since then, digital seismometers have moved the research forward. It seems that it is strongest during storms but the pulse is constant. In 2005, Greg Bensen at the University of Colorado-Boulder noted a strong signal, coming from somewhere far off.  His team considered possible sources – instrument error, incorrect data analysis, or that this seismic activity was real. They were even able to triangulate the pulse to a single source in the Gulf of Guinea, off the western coast of Africa.

But is it caused by waves? Volcanic activity?

It’s interesting but not particularly shocking or new. There is seismic activity all the time, not just during an earthquake or volcanic eruption.

Another way to look at it is to point to the Sun which heats the Earth more at the equator than at the poles and creates winds and storms and ocean currents and waves. When a wave hits a coastline or the continental shelf, the energy is transferred to the land and the pressure deforms the ocean floor.

Other scientists still favor the volcanic explanation. The pulse’s origin point is close to a volcano on the island of São Tomé in the Bight of Bonny.

And other scientists say that why is the pulse there when there are other continental shelves and volcanoes around the world. Why aren’t there other pulses?

I like scientific studies that are still unsolved after more than a half-century. I like the mystery. And I like that the planet has a pulse.

If we look beyond our planet, astronomers think they’ve solved a cosmic mystery surrounding fast radio bursts – powerful emissions of radio waves in space. Astronomers believe they have been able to track a burst back to a type of dense star called a magnetar. Magnetars have more mass than our sun but are squeezed into an area about the size of Manhattan. They occasionally spew bursts of radio waves and that’s what’s been causing the mysterious phenomenon lately. The bursts aren’t dangerous to humans.

One theory before this was that it was an alien signal.  That one was less scientific but certainly more fun. It would really be exciting if the Earth’s pulse came from radio waves sent here by aliens. No one seems to be investigating that possibility though.

Shakespeare’s Moons

A proportionate image of Uranus’ large moons and one smaller moon: from left to right Puck, Miranda, Ariel, Umbriel, Titania and Oberon. Images via NASA’s Voyager 2

“Well shone, Moon. Truly, the moon shines with a good grace.” – A Midsummer Night’s Dream

The moons that orbit planets in our solar system other than our own mostly have names from ancient mythologies.  Uranus’ moons are unique in being named for Shakespearean characters and a few named for characters from the works of Alexander Pope.

“Sweet Moon, I thank thee for thy sunny beams; I thank thee, Moon, for shining now so bright.”  –  A Midsummer Night’s Dream

Oberon and Titania, a King and Queen from A Midsummer Night’s Dream, are logically the names of the largest Uranian moons. They were the first ones to be discovered by William Herschel in 1787.

The next two discovered were named Ariel and Umbriel. In 1948, Miranda was discovered.

It wasn’t an astronomer but the Voyager 2 spacecraft visited that found ten more moons orbiting in 1986. They were named Juliet, Puck, Cordelia, Ophelia, Bianca, Desdemona, Portia, Rosalind, Cressida, and Belinda.

Astronomers using the Hubble Space Telescope and powerful ground-based telescopes have increased the number of moons Uranian moons to 27! They are small (12-16 km or 8-10 miles across). They are black and, being 2.9 billion km (1.8 billion miles) away from the Sun, they are composed half of water ice and half of rock.

A lonely Miranda by John William Waterhouse, 1875

Miranda is from my personal favorite of Shakespeare’s plays – The Tempest. She is the only female character to appear on stage. She is the daughter of Prospero, a wizard banished to the island setting. Miranda was 3 years old when they arrived there and has only known her father and their servant Caliban for her 12 years there.

It is reasonable to consider that island setting as being influenced by explorations of the New World (North America). We believe that Shakespeare wrote the play in 1610-1611 and from 1607–1611 Henry Hudson explored Greenland and the river, strait and bay that now carry his name. Reports of the New World probably reached Shakespeare in the news along with tales of exotic plants, animals and people encountered or imagined. Caliban is an anagram of “cannibal.”

When Miranda first sees shipwrecked men arrive on the island, she says:
O, wonder!
How many goodly creatures are there here!
How beauteous mankind is! O brave new world,
That has such people in’t!

Like discovering a new moon or planet, it is wondrous – but Prospero reminds her and us that ‘Tis new to thee,” but of course they were always there.

According to NASA, Miranda, the innermost and smallest of the five major satellites, is unique. It has giant fault canyons that are as much as 12 times as deep as the Grand Canyon.

Uranus’ icy moon Miranda – Image from Voyager 2 NASA/Jet Propulsion Laboratory

The moon Ariel is named for a spirit in The Tempest. The name Ariel means Lion of God, but Shakespeare probably meant it was a play on the word “aerial” since this spirit is supposed to fly around the island. The moon itself is the brightest and possibly the youngest of the moons of Uranus.

And following Shakespeare’s characters, Oberon, Shakespeare’s King of the Fairies in A Midsummer Night’s Dream, is an older, heavily cratered moon.

Shakespeare’s writing and characters live on in many ways.