Ken Tapping – August 5, 2022 / 04:00 | History: 378743
Photo: Greg Reely
Unique once-in-a-lifetime image of a comet taken by local South Okanagan photographer near Cawston.
If you want to make a comet, an asteroid, a planet, a star, or many other bodies, the recipe is the same. There is only one ingredient: cosmic clouds of gas and dust.
The procedure is the same, only part of the material is assembled in one piece. What you end up with is entirely determined by the size of the dough you’re working with. The mass of the lump determines two critical quantities, the pressure and the temperature at the core of this body.
The temperature at the Earth’s core is about 5,200 C and the pressure about 3.6 million times the atmospheric pressure at the surface. The pressure comes from the weight of the rock above it. The internal heat comes from two sources: the energy released by the impacts of incoming objects when the Earth was formed, about 4.5 billion years ago, and from the decay of radioactive elements present in the cosmic material.
For a planet our size, heat escapes very slowly. For smaller worlds, the process is faster.
Imagine that somewhere in a great cloud of cosmic dust and gas, a couple of grains drift in and, thanks to static electricity or something else, stick together. The resulting grain is larger and presents a larger target for other particles, so it has a better chance of catching more particles. Even in these clouds, the density of material is very low, so collisions are rare, but they happen a long, long time.
As the grain grows, it collects samples of all the chemicals that make up the cloud, including hydrogen and other volatiles. Eventually, it goes from being a grain to a lump, and after more time it becomes massive enough that a new force takes over to hold the lump together and increase its rate of growth by dragging more and more of the surrounding material: gravity.
The impact of the new material on the growing lump causes it to heat up, melt so that when it gets big enough and its gravity is strong enough, it is stretched into a sphere, perhaps a thousand kilometers in diameter. It is now a large asteroid. Continued impacts produce more heat. Of course, the formation process can stop at any time, allowing the object to cool and eventually solidify throughout the process. However, in our case the growth continues. When it reaches a diameter of several thousand kilometers, it has graduated as a planet.
If our new planet is close enough to a star, the star’s heat will evaporate and expel most of the gas and other volatile material, so we end up with a rocky planet, like Mercury, Venus, the Earth or Mars
On the other hand, if the planet manages to hold on to its gas and volatiles, it can become a gas giant planet, like Jupiter, Saturn, Uranus and Neptune. During their formation, these planets collected a large amount of internal heat, so even today their cores are extremely hot.
Now things get very interesting. If our planet collects material to the point where it exceeds about 20 times the mass of Jupiter, the central pressure and temperature are high enough for some elements, such as deuterium and lithium, to undergo nuclear fusion, producing energy. It’s no longer a planet and it’s not yet a star, which gets its energy by fusing hydrogen.
Objects like this, a star not very bright, are known as brown dwarfs. These objects show some aspects of star behavior, such as flaring. Astronomers are very interested in them. If the material keeps coming, and our star reaches 100 or more Jupiter masses of material, we have a new star.
It’s amazing what you can do with one recipe, one ingredient and just changing the amount.
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• Saturn rises shortly after sunset, followed a couple of hours later by Jupiter. After two hours or so, Mars comes into view, followed, just as the sky begins to light up with dawn, by Venus.
• The Moon will be full on the 11th.
This article is written by or on behalf of an outsourced columnist and does not necessarily reflect the views of Castanet.
Ken Tapping – July 29, 2022 / 04:00 | History: 377609
Photo: NASA
The James Webb Space Telescope
One of the goals of the James Webb Space Telescope is to find out when shortly after the Big Bang galaxies began to form and when stars began to make the elements needed to make planets and life.
The JWST is just getting into action, but it’s already giving us some strong hints. This kind of study is possible because looking at ever greater distances takes us back in time. Although light travels very quickly, cosmic distances are so great that light from stars and galaxies can take anywhere from years to billions of years to reach us, depending on how far away they are.
Expressing these distances in kilometers leads to extremely large numbers, which are difficult to visualize. We often express these distances in “light years”, which is the distance light travels in one year. If we look at a galaxy located a billion light-years away, we are seeing it as it was when that light came our way, a billion years ago.
By looking at increasingly distant objects, we see the universe as it was further back in its history. Telescopes are time machines. Recent observations using the JWST show us that galaxies like ours existed only 600 million years after the Big Bang, just under 14 billion years ago.
The oldest and most distant thing we can see is the cosmic microwave background, or CMB. This dates back to about 380,000 years after the Big Bang, the beginning of the universe, about 13.8 billion years ago.
The CMB is basically a nearly uniform glow across the sky, emitted when the universe had expanded and cooled enough for light to travel through. However, when this glow is accurately mapped, we see small variations in temperature. These mark clumps of material, collapsing under their own gravity, on their way to becoming the first galaxies.
When the universe became transparent, there were no stars to illuminate it. It was dark. We often refer to the period of time between the CMB and the first stars as the “Cosmic Dark Age”.
We would really like to know when this era ended and the first stars and galaxies were formed. We’re doing this by using our ever-improving instruments to move forward from Earth and back in time, until we stop seeing galaxies or, hopefully, see the first galaxies and stars forming.
Of course, when we see one of these distant, dim galaxies, we need to know how far away it is and, from here, how far back in time we’re looking. Measuring such large distances directly is extremely difficult. Fortunately, there is a simple and fairly reliable indirect method. We use the expansion of the universe.
This has been accurately measured over decades of work. The rate at which a distant galaxy is being swept away from us by the expansion of the universe is directly related to how far away it is. A galaxy twice as far away from us as another will recede twice as fast.
The relationship between recession speed and distance has been widely measured and is known as the Hubble constant.
Measuring the recession rate of a galaxy is pretty easy, so we apply the Hubble constant and get a pretty good idea of how far away that galaxy is. So the search is for fainter and fainter galaxies moving away from us at ever higher speeds, placing them at greater and greater distances. This requires ever better telescopes, like the JWST.
JWST has only just started operating, so its discovery of normal-looking galaxies that exist only 600 million years after the Big Bang is encouraging. His training must have started very quickly. At this point we still don’t know how fast, because we haven’t gone far enough back in time yet.
Watch this space.
•••
• Before dawn, Saturn is low in the south, with bright Jupiter to the left, then Mars and finally Venus, in the dawn glow.
• The Moon will reach its first quarter on July 5.
This article is written by or on behalf of an outsourced columnist and does not necessarily reflect the views of Castanet.
Contributed – July 22, 2022 / 04:00 | History: 376511
Photo: smithcube.wilsonema.com
The James Webb Space Telescope (JWST) is almost in its parking lot, 1.5 million kilometers from Earth.
It is fully functional and sends beautiful images.
Its 6.5-meter mirror, made up of 18 hexagonal segments, is fully deployed, with all of these segments located a millionth of a meter apart (the spacecraft had to be folded to fit the launcher).
The mirror is larger than that of the Hubble Space Telescope (HST); it can collect about seven times more light and discern finer details. It will supplement rather than replace the HST.
Instead of observing visible light, which is HST’s goal, JWST will observe primarily at infrared wavelengths. This makes it better for looking at the formation of stars and planets and for exploring the most remote regions of the universe.
Putting telescopes into space is a big job and it’s expensive, and there won’t be anyone there if something goes wrong during setup.
The problems with the HST were manageable because its low orbit made it accessible via the Space Shuttle. We currently have no easy means of getting a service engineer on the James Webb Space Telescope.
Ground-based telescopes can be made larger, and telescope instruments can be easily changed to keep up with evolving scientific needs. If something breaks, it can be fixed. So, given the enormous additional expense and challenges involved in putting telescopes into space, why do it?
If you look at a star through a telescope, most nights you’ll see a drop, dancing around and flashing different colors, when you should be seeing a dot of color. The moon and planets can…