Facination with 'magical' solar eclipses

Another eclipse story

The events of April 8 show solar eclipses are very special to us.

It is not just a matter of the comparatively rare event of the Moon passing in front of the Sun. For many, the spectacle makes us feel part of something immensely bigger, which is beyond our control. Our fascination with solar eclipses is probably as old as humanity. Long before Isaac Newton, Johannes Kepler and others who made it possible for us to precisely analyze the orbits of objects in space, our ancestors studied the rhythms of the heavens and could predict solar eclipses with great accuracy. Woe betide the astronomer who failed to predict one.

We have a situation that must be extremely rare in the universe. From Earth, the Moon looks as big in the sky as the Sun, making it possible to cover the bright solar disc completely, revealing the pink loops and other structures in the solar chromosphere, and the pale streamers of the solar corona.

There is a down side. As the Moon interacts with our oceans—making the tides—the force of our oceans on the Moon is making it gradually move further out into space. One day it will appear too small to cover the solar disc, bringing our current magical era to an end.

Some years ago, I was returning to Canada from a meeting in Europe and took the opportunity to stop over in the United Kingdom for a few days to see some friends and fellow scientists. It just so happened there was to be a total solar eclipse, visible from Devon and Cornwall in southwest England.

I had no scientific plans for the eclipse and just planned to enjoy the spectacle and feel the awe. I stayed with some friends in Sussex, in the southeast, on the edge of the path of totality, and planned to take a train down to the eclipse site.

However, the weather forecast was horrible. Southwest England was headed for several days of heavy cloud and intermittent rain. One wry joke about Devon is: "Welcome to Devon, where it rains eight days out of seven".

On the other hand, Sussex was to be clear, cloudless and sunny. I decided a marginal eclipse in Sussex would be better than standing watching the clouds get darker as the rain ran down my neck. So we elected to set up some equipment for safe solar observations in the backyard in Sussex, with a picnic and bottle of wine to toast the Sun.

The eclipse day in Sussex dawned sunny with a completely cloudless sky. Devon and Cornwall got clouds and heavy rain. At the predicted time, the solar disc showed a dark nibble—the edge of the Moon. It slowly got bigger, and as more of the disc was covered, it got darker. However, our eyes are highly adaptable and so the main effect was finding colours harder to see and it getting harder for our eyes to focus.

Eventually, the entire solar disc was covered apart from an incredibly thin, thread-like crescent, with darker gaps where the light was blocked by lunar mountains.

When experiencing eclipses, it is important to not only to watch the Sun—we need to watch our surroundings. When the solar disc was covered but for that thin thread of light, the trees all looked odd, showing sparkly patterns that shifted in the wind. The ground was covered with crescents of all sizes, moving, appearing and vanishing. Gaps between the leaves on the trees acted as pinhole cameras, projecting images of that solar crescent on each other and on the ground beneath.

Then, the crescent broadened as the Moon moved on and our surroundings started to brighten again. We must have had just a bare instant of totality but the experience was one I will never forget.

Eclipses offer not only opportunities for scientific research into how the Sun works and how it interacts with the Earth, but also into the fascinating issue of how we respond to eclipses.


• Venus lies extremely low in the dawn glow.

• Jupiter shines very low in the west after sunset.

• The Moon will be full on April 23

This article is written by or on behalf of an outsourced columnist and does not necessarily reflect the views of Castanet.


Figuring out what occurred in the galaxy before the Big Bang

Before the Big Bang

For much of our history, we have conceived the universe as something eternal, in which everything we know of comes and goes.

Then, in the first half of the 20th century, Georges Lemaitre, a Roman Catholic priest and a brilliant physicist, proposed the known-to-be expanding universe points back to a time when everything was concentrated in one lump. He called the "primaeval atom".

This That primaeval atom then started to expand, leading to the universe we have around us today. Einstein disagreed, although his calculations proved Lemaitre right, and eminent astrophysicist Fred Hoyle, would not accept the idea of a beginning, and came up with the derisive term: "These men with their Big Bang".

That name stuck, although not in the way Hoyle expected.

The fading breath of the Big Bang has since been detected, mapped and studied. The universe is expanding, and the young universe was different from what exists today. There was a beginning, and probably will be an end.

An early possible answer to both these questions came from the "Big Crunch Theory". If everything is gravitationally pulling at everything else in the universe, we would expect the expansion we see to gradually slow, and possibly stop. Then everything would start falling inward again until at some point in the far future there would be a big “crunch,” with everything back in one compact lump, a repeat of Lemaitre's primaeval atom.

Then, at some point, that would undergo a “big bang,” and the whole universal process would start over again. This provided a very convenient answer to the questions as to what came before, and what comes after—one universe after another.

Unfortunately, this convenient idea was ruled out by our subsequent observation that the expansion of the universe is not slowing towards a new big crunch. The expansion is accelerating. This suggests the universe will expand, becoming more and more rarefied, with all the stars eventually running out of fuel.

At some point the particles making up the atoms of our stars, worlds, and us, will decay, and everything will finally fade away. Would a better understanding of the beginning of the universe help us here? Unfortunately, as yet that part of our universe's history is unobservable.

Until about 380,000 years after the Big Bang, the universe was an incredibly hot, dense, glowing fog. At the moment, we can only work our way further back towards the beginning through calculation. However, our knowledge of physics has been derived under the conditions we see around us now, or produce in the laboratory. This does not help us understand the extreme conditions after the Big Bang.

An idea currently enjoying a lot of interest is the existence of an eternal "multiverse", in which universes form, expand and dissipate, like bubbles in a "cosmic foam". Apart from making imaginative calculations, is there something concrete we can do to establish whether this foam exists?

It has been suggested that in foams, bubbles are often in contact with other bubbles. At these contact surfaces, the curvature is different, as we see when taking a bath with lots of bubbles. We might be able to see the contact faces with other universes by searching the sky for patches of sky that are different. The most distant region of space we can see is the cosmic microwave background, that point 380,000 years after the beginning when the fog cleared.

The search is on for unusual patches in that. Nothing has been found yet.

Of course, invoking a multiverse in which universes like ours form, expand and then dissipate is only pushing the big question back another level. Did the multiverse have a beginning, or is it eternal? Can we answer that?


• Venus lies extremely low in the dawn glow.

• Jupiter shines low in the west after sunset.

• The Moon will reach its first quarter on April 15.

This article is written by or on behalf of an outsourced columnist and does not necessarily reflect the views of Castanet.

Measurements of radiation around Earth marked early days of Space Age

Earth's radiation belts

The Space Age began on Oct. 4, 1957, when the Soviet Union launched the Earth's first artificial satellite.

At the time, the Cold War was in full swing, with the world's power blocs competing for power and prestige. With the launch of that first satellite, called Sputnik (Russian for "little traveller"), the then-USSR scored a major goal in the prestige competition. At that time, the only other country actively working on launching spacecraft into orbit was the United States, with its Project Vanguard.

The fact a Russian satellite was passing overhead several times each day, transmitting its "bleep, bleep" signals on a frequency almost all radio amateurs could hear, pushed Project Vanguard into high gear.

The Soviet satellite was launched using an inter-continental ballistic missile (ICBM), sending the not-so-subtle message that if the missile could put a satellite into orbit, it could be used to attack anywhere on Earth. However, Project Vanguard was completely different. The launcher rocket was being specifically developed for launching satellites. The program for developing ballistic missile weapons was entirely separate.

An attempted launch of the Vanguard launcher with a satellite in December that year failed spectacularly. A backup plan was quickly put into action. An intermediate range ballistic missile (IRBM) was modified for launching a satellite, and a satellite, known as Explorer1, was hastily put together.

With time and weight constraints, the number of onboard instruments was limited to four, the main one being a Geiger counter. This device, invented by Hans Geiger and Walther Müller, is a device for detecting high-energy particles, such as those produced by radioactive materials. It was known there were high-energy particles in space, coming from the Sun and other sources.

Explorer 1 was successfully launched on Feb. 1, 1958. The speed with which it was achieved is a real indicator of what can be done if it is wanted enough. Unlike Sputnik, which was in a near-circular orbit, Explorer's orbit was highly elliptical, ranging between 358 and 2,550 kilometres from the Earth.

As the spacecraft moved around its orbit, the scientists noted something odd. When it was close to the Earth, the Geiger counter was detecting the expected 30 or so counts per second due to cosmic radiation particles. However, as Explorer moved towards the highest part of its orbit, the count rate increased and then suddenly dropped to zero. This caused some puzzlement, until it was realized that the Geiger counter was encountering such high count rates it was overloading and reporting zero. This was not expected.

As the spacecraft moved to and fro between the lowest and highest points in its orbit (referred to in astronomy and space science as the perigee and apogee respectively), the Geiger counter data showed the Earth was surrounded by two radiation belts. These were named the inner and outer van Allen belts, after a magnetospheric physicist who pioneered putting scientific instruments on satellites. These radiation belts are made up of mainly high-energy particles from the Sun that had become trapped in the Earth's magnetic field. They are not strong enough to endanger astronauts.

Spacecraft flying past Jupiter and exploring the Jupiter system showed the giant planet has an intense magnetic field filled with enough high-energy particles to damage spacecraft electronics and pose a very severe hazard for human astronauts. Saturn, Uranus and Neptune have radiation belts too.

Most planets probably have them, with the stronger the magnetic field, the higher the radiation hazard.


• Venus and Mars lie extremely low in the dawn glow.

• Jupiter shines low in the west after sunset.

• The Moon will be new on April 8.

This article is written by or on behalf of an outsourced columnist and does not necessarily reflect the views of Castanet.


Solutions sought to measuring speed and distance travelled by planets in space

Trouble with Hubble

Our knowledge of the expansion of the universe is fundamental to understanding how it formed and how it has and is evolving.

That expansion was first measured by Edwin Hubble. He compared measurements of how far away galaxies lie with the speeds they are receding from us. The relationship between the distance and the speed of recession is known as Hubble's Constant. We have a problem with chaining down the precise value of Hubble's Constant and hoped observations made using the James Webb Space Telescope would resolve the issue. However, unfortunately, it has made things worse.

It is fairly easy to measure the speed with which a distant galaxy is receding (or approaching). We use spectroscopes to detect the signatures of particular elements in the light from that galaxy. If the object is receding from us, we will see those signatures shifted to longer wavelengths, that is, reddened. The amount of the reddening, or "the red-shift", gives us the speed.

Getting distances is a bit harder. Fortunately there is a class of variable stars called cepheids. These stars cycle in brightness, and the duration of each cycle is related to the average brightness of the star. We search images of distant galaxies for cepheids, and then measure how long each cycle of brightness changes takes. We can then calculate the light energy output (the luminosity) of the star and compare that with the observed brightness.

That will tell us how far away it is. If we measure the brightness of a distant light, and know that it is a 100-Watt light, we can calculate how far away it is. So by searching for thousands of cepheids lying in distant galaxies, and measuring their red-shift, we can evaluate Hubble's Constant and calculate how long ago everything in the universe was in one lump. Measurements made using the Hubble Space Telescope have been a mainstay of this work. The value obtained for Hubble's Constant was about 74 kilometres a second per million parsecs. That is, for each additional million parsecs of distance, the recession speed of galaxies as they are carried away by the expansion of the universe increases by 76 kilometres a second. A parsec is a unit of distance, and is equal to about 3.26e13 km.

There is another method for determining Hubble's Constant. That involves looking at the tiny irregularities in the cosmic microwave background, the fading breath of the Big Bang. That originated 380,000 years after the beginning, when, for the first time the universe cooled enough for atoms to come together, allowing light to travel through it. That method is also believed reliable, but gives a different answer—67 kilometres a second per million parsecs.

This discrepancy was widely believed to be measurement errors, and more precise determinations would resolve the issue.

That is where the James Webb Space Telescope came in. However, a long series of measurements yielded an answer that agreed well with the measurements made using the Hubble Space Telescope, So, that discrepancy between the results obtained using the two different methods of measurement is real. Could it be that the two sets of measurements are not really describing the same thing?

Many possibilities are being looked at. One of them is a revival of an idea suggested a long time ago to explain the reddening of the light from distant galaxies. The idea is, as it travels over cosmic distances, light loses energy, it gets "tired". When light loses energy it becomes redder. That may explain why the measured red-shifts are higher than expected. There are other possibilities, so the next year or two should be interesting.


• Venus and Mars lie extremely low in the dawn glow.

• Jupiter shines in the west after sunset, with Mercury hiding low in the sunset glow.

• The Moon will reach its last quarter on April 1.

This article is written by or on behalf of an outsourced columnist and does not necessarily reflect the views of Castanet.

More Skywatching articles

About the Author

Ken Tapping is an astronomer born in the U.K. He has been with the National Research Council since 1975 and moved to the Okanagan in 1990.  

He plays guitar with a couple of local jazz bands and has written weekly astronomy articles since 1992. 

Tapping has a doctorate from the University of Utrecht in The Netherlands.

[email protected]

The views expressed are strictly those of the author and not necessarily those of Castanet. Castanet does not warrant the contents.

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