The NSF Rubin Observatory Credit: Rubin Observatory/NOIRLab/NSF/AURA/P. Horálek (Institute of Physics in Opava) government photograph in the public domain.

Comets are deeply mysterious and have sought since antiquity. The earliest written records of comets date back to ancient Babylon, around 500 BC, and many cultures interpreted these celestial phenomena as omens or messages from the gods. However, it wasn’t until the 16th century that the scientific study of comets began to truly take shape.

In 1531, the German astronomer Michael Maestlin documented the return of a comet, marking one of the first instances where an astronomer connected a comet’s periodic nature with the idea that it was an object in orbit around the Sun. Later, in 1682, the famous English astronomer Edmond Halley observed that a comet which had appeared in 1607 and 1682 was the same object, suggesting comets had elliptical orbits. Halley’s Comet, helped establish the idea that comets were not random in their appearance but part of our solar system’s clockwork mechanism.

The first comet discovered through a telescope was in 1618, when Johannes Kepler used his observations of the night sky to note the presence of a comet near the constellation of Andromeda. The 19th and early 20th centuries saw an expansion of observatories and technological advancements in telescopes. The invention of photographic plates in the late 1800s allowed astronomers to capture images of the night sky with far more detail than ever before. As a result, astronomers could begin scanning vast sections of the sky in search of moving objects that could be comets.

In the 20th century, the rise of professional comet hunting truly took off with large telescopes, and the introduction of wide-field surveys helped make discoveries more routine. Observatories like the Mount Wilson Observatory in California, the Palomar Observatory, and the Mauna Kea Observatory in Hawaii became central to the discovery of new comets, some of which became famous in their own right, such as Comet Hale-Bopp (1995) and Comet NEOWISE (2020).

Today, many of the world’s most powerful telescopes are still in use for comet hunting. These observatories often employ both optical and infrared technologies to scan the night sky for signs of a comet’s unique characteristics: a bright core (nucleus) and a long tail.

Some of the most notable modern observatories include:

• The Pan-STARRS (Panoramic Survey Telescope and Rapid Response System): Located in Hawaii, Pan-STARRS is known for its wide-field sky surveys. This observatory has discovered hundreds of asteroids and comets, often catching those that could potentially impact Earth.
• The Sloan Digital Sky Survey (SDSS): Using the Apache Point Observatory in New Mexico, SDSS has mapped a vast portion of the sky, leading to the discovery of several comets, as well as asteroids, galaxies, and other astronomical phenomena.
• The Catalina Sky Survey: Based in Arizona, this project focuses on detecting near-Earth objects (NEOs), including comets. It is part of the search for hazardous asteroids and comets that could pose a threat to Earth.
• The European Southern Observatory (ESO): Operating several telescopes across Chile, the ESO is instrumental in comet research, providing valuable data to both professional and amateur astronomers.

If you look in a modern comet observing guide, such as Sky Safari, you will often see the names of these observatories and widefield comet scans attached to some of the major and most dramatic modern comets. This includes the comet that we have been talking about C/2023 Tsuchinshan Atlas A3. What’s in a name. Tsuchinshan: This part of the name is derived from the Tsuchinshan Observatory, which is located in China. Atlas: This part refers to the ATLAS (Asteroid Terrestrial-impact Last Alert System) survey, which is an automated system that scans the sky for asteroids and comets, especially those that could potentially impact Earth.  A3: This part of the name is used to indicate the sequence of the comet’s discovery within that particular year. In this case, A3 signifies that this is the third comet discovered in 2023 that has been assigned a name in the “A” group. The “A” typically represents the first half of the year.

However, as I write there is a major game changer in comet, and asteroid, and novae  on the horizon [sic]. Coming on line this year is the launch of  Vera C. Rubin Observatory in Chile’s Atacama Desert. It will feature  a 8.4-meter telescope. If like me, you grew up when the 200 inch telescope at Palomar was king, pause a moment and recognize that that is ~328 inches.  The telescope is equipped with a state-of-the-art camera with a field of view larger than that of any previous sky survey telescope. It can capture the entire sky continuously every three nights looking for the telltale changes due to asteroids, comets, and novae. The observatory’s primary mission is to conduct the Legacy Survey of Space and Time (LSST), a 10-year project that will scan the entire sky repeatedly, providing a treasure trove of data on asteroids, comets, and other celestial objects.

The camera at the Vera Rubin Observatory has an extremely wide field of view that spans about 9.6 square degrees (that’s ~ twenty moon diameters). Its 3.2 gigapixel detector, will be the largest digital camera in the world. All of this boils down to a spatial resolution of about 0.2 arcseconds per pixel.

It once was true that revolution was rare, particularly scientific revolution. Now as we aspire to the singularity they are ever more familiar. Ten years from now we will speak very differently about the solar system and the universe. Vera Rubin will enable us to lift up a thousand veils and extend relentlessly the margins of the known universe.

I am part of all that I have met;
Yet all experience is an arch wherethrough
Gleams that untraveled world, whose margin fades
For ever and for ever when I move.

Ulysses

Alfred, Lord Tennyson

Figure 1 – Comet C/2023 A3 – Tusuchinshan Atlas from Spy Pond in Arlington, MA, ISO 800, 1 sec F/4 70 – 200 mm Zoom on October 12, 2024. (c) DE Wolf 2024

When I was teenage Davy and obsessed with astronomy I dreamt with wonder at the coming of Comet Halley in 1986. I was to be an impossibly old man at that date, although not as old as I would be at the coming of the millennium. I waited and many things happened. Finally, one night I went out to find the great comet. I searched the sky, star map in hand, with my father’s binoculars. I remember the moment vividly.

“So the years spin by and now the boy is twenty
Though his dreams have lost some grandeur coming true
There’ll be new dreams maybe better dreams and plenty
Before the last revolving year is through.“

The Circle Game, Joni Mitchell

The 1986 appearance of Comet Halley, compared to it predecessors, was kind of a dud. And we were left to new dreams, since none of us would live to see Halley come again.

“Comets are like cats: they have tails, and they do precisely what they want.”

David H. Levy

Fortunately, there have been other comets, which have lived up to the dream and mystery. In 2024, we were graced this fall with the appearance of Comet C2023 3A Tusuchinshan-Atlas – so wonderful! TC and I went out to Spy Pond in Arlington, MA. She wisely waited in the car listening to Bach, while I stood with a small crowd of nerdy Cambridge people waiting and stared in the chilly, setting light at the brilliance of Venus hovering above the horizon. Then we say it!

For comets in twilight, where the goal is to capture as much of the tail as possible I like to set up my Canon T6 with my 70 to 200 mm zoom on a tripod and take a wide open shot at something like 10 seconds. Figure 1 is the result, a spectacular comet against a cream blue sky.

Truly this comet was not a disappointment.  Comets have captivated humanity for millennia, inspiring awe and curiosity. These icy visitors from the far reaches of the solar system have been the subject of myths, legends, and scientific studies alike. They have been seen as harbingers of change, foretelling great battles won and lost.

“When beggars die, there are no comets seen: the heavens themselves blaze forth the death of princes.”

William Shakespeare

To the Elizabethans, who believed that the world was meant to be static the sudden appearance of these hairy mysteries could be terrifying.

As Hamlet says, “Time is out of joint. Oh cursed spite, that ever I was born to set it right.”

At their core, comets are icy bodies that orbit the Sun. They are composed primarily of frozen water, gases, and dust. Unlike planets or asteroids, comets have highly elliptical (elongated) orbits, which means they spend much of their time far from the Sun before making a dramatic, close approach.

When a comet gets near the Sun, the heat causes its ices to sublimate (change directly from solid to gas), releasing gas and dust into space. This process creates a glowing coma (a cloud of gas and dust) and often a bright, visible tail that points away from the Sun.

Comet tails, in fact, come in three distinct types, each created by different interactions between the comet, the solar wind, and the Sun.

Dust Tail:
This is the most visible and often the brightest tail. The dust tail forms from small, solid particles (mostly dust) that are released as the comet’s icy nucleus heats up and begins to sublimate as it gets closer to the Sun. These particles are pushed away from the Sun by the pressure of sunlight. The dust tail tends to be broad and curved, following the comet’s orbit.

Ion Tail (Plasma Tail):
The ion tail is created when the comet’s gases (mostly water vapor, carbon dioxide, and other compounds) ionize due to the intense ultraviolet radiation from the Sun. The solar wind then carries these charged particles away from the comet, forming a tail that always points directly away from the Sun. The ion tail is often faint and blue due to the ionized gas, and it’s more straight compared to the dust tail.

Antitail:
This one is a bit more unusual. An antitail occurs when the comet’s orbit is such that, from our perspective on Earth, the ion tail appears to point in the opposite direction to the Sun. This phenomenon can happen when the comet is moving away from the Sun and the ion tail is still pushed by the solar wind. The antitail appears as a faint feature, and it’s not visible in all comets. But it was brilliantly visible with comet C/2023 3A.

Comets are believed to be leftovers from the early solar system. They are said to be “cosmic time capsules,”  When our Sun and planets formed about 4.6 billion years ago, the outer regions of the solar system were home to many icy bodies that never coalesced into planets or moons. These icy bodies, known as cometary nuclei, contain some of the most primitive material in the solar system and are thought to have been preserved in their original state since the formation of the solar system.

There are two main regions in the solar system where comets originate: The Kuiper Belt: Located just beyond Neptune, the Kuiper Belt is home to short-period comets, which have orbits that last less than 200 years. These comets come from a relatively stable region and are believed to be remnants from the solar system’s early years. The Oort Cloud: A much more distant and hypothetical region, the Oort Cloud is thought to be a vast sphere of icy bodies that could contain long-period comets (those that take more than 200 years to orbit the Sun). These comets are often sent into the inner solar system by gravitational interactions with nearby stars.

These are just some basic facts about comets. Along with asteroids, they are very ancient objects which present in an unspoiled way the very beginnings of our solar system four plus billion years ago, We can visit them now, and in so doing sample our very own origins. Always there is the wonderful dichotomy between the physics of comets and the metaphysics of wonder at these cosmic voyagers some visiting us over and over again with clocklike regularity; others fleetingly passing us but once.

“Old men and comets have been reverenced for the same reason: their long beards, and pretences to foretell events.”

Jonathan Swift

Figure 1 – Comet Tusuchinshan Atlas bidding farewell to Earth and Earthlings on October 27, 2024 seen here with the SeeStar 50s. Five minute exposure. (c) DE Wolf 2024

You may have noted a paucity of blogs here lately. I have finally come to grips with the fact that my photography over the last year has become more and more astrophotography. Astronomy was the keystone of my nerd days in my teens. Whom am I fooling? I am still a major techno-nerd. In those days I had a wonderful 60 mm Unitron refractor, would stand on the shores of New York’s East River and well, observe! My eyes were clearer then and the skies of The City were clearer then. About eight years ago I bought a wonderful Skywatcher 127 mm Maksutov telescope – more wonderful observing! I won’t go on and on with each telescope bought and used. Sufficeth it to say that I am the proverbial “pig in slop.” But last year something important happened – the advent of AI smart telescopes. I purchased the ZWO SeeStar 50s and my adventure in Astrophotography began. Teenage Davy may feel happy and fulfilled!

The ZWO Seestar 50s is the ideal low-budget entry companion to personal astrophotography. Released in 2023, the ZWO Seestar 50s is ZWO’s first smart telescope, You basically set it up and tell it what you want to look at. It’s smart! Actually, its been getting smarter and smarter, easier and easier to use as the firmware evolves.

The Seestar 50s is truly built with beginners in mind. Its intuitive controls and mobile app make it easy to operate. The automatic GOTO and tracking capabilities simplify locating celestial objects (always a bugaboo in the past) and make the stargazing experience hassle-free.

The amazing technical specs are:

• Aperture: 50mm
• Focal Length: 250mm (f/5 ratio)
• Sensor: Sony IMX462 (2 megapixels)
• Battery: 6000mAh, Lithium
• Image Formats: JPG, FITS, MP4, AVI RAW
• Dimensions: 10.2 x 5.6 x 5.2 inches
• Weight: 5.5 pounds

There are, of course, both pros and cons, particularly the fact that it is less than ideal for planets, and at this point I think I have largely grown beyond it. BUT it is the ideal travel scope and leaves room in my backpack for, well, clothes and candy bars.

The Observacar you ask? This is key to the experience. I set my smart telescope up and then control it with my iPad from my car. I’m warm and toasty in winter, cool and bug free in summer. And yes, I always try to pop my head out and marvel at the night sky regularly, to marvel like men and women over all the ages at the glories of the distant light.