On Christmas morning of 2021, the James Webb Space Telescope successfully launched from Earth. Thomas Zurbuchen, now NASA's associate administrator for science, had made the call. If Webb was going to fail, he would take the blame.

Not only did Webb launch, but its Ariane 5 rocket performed the flight with such precision that the spacecraft was able to save precious fuel for maneuvering, thereby extending its lifetime. Over the next two weeks, engineers and scientists executed hundreds of steps to unfold and fully extend the telescope and its massive sunshield. And then, finally, on Monday, the spacecraft performed one final major burn of its thrusters, falling into a halo orbit around the L2 point.

This means that the Webb space telescope has reached its final destination, a 180-day orbit around this L2 point, which keeps the telescope in line with the Earth as both the instrument and planet orbit around the Sun. Here, while using a minimum amount of fuel to hold its position, Webb can use its sunshield to keep the infrared telescope and its instruments cold.

The work is not done. The telescope has 18 primary mirror segments, which are moved by 132 actuators. These actuators have already been tested and shown to work. Now, over the next three months, telescope operators will fine-tune the alignment of these mirrors. During this process, scientists will use a Sun-like star named HD84406 to focus the mirrors. This star is located about 240 light years from Earth and can be found in Ursa Major near the bowl of the Big Dipper.

At the same time, in the wake of the sunshield, these mirrors and their scientific instruments will continue to cool in order to be able to detect the weak, ultra-distant signals of heat from the Universe's oldest galaxies. //

What is it about HD84406 that makes it the one to use for focusing the mirrors?

There are probably lots of criteria, but I only know two of them:

1. It's in the same 1/3 of space that JWST can see (i.e. the telescope doesn't have to look towards the Sun to see it)
2. It has to be relatively bright (HD84406 is not visible to the naked eye but can be seen with binoculars).

I can't find a reference now, but IIRC it was also selected because it's isolated with nothing behind it that's close (in interstellar terms), so it's easier to determine if the focus is good because there's less background light.

Japanese Geostationary Satellite 'Himawari-8' captured an eruption of a volcano near Tonga. Not only the eruption but also the shock wave can be seen. On the other hand, the terminator between daylight and night caught up with the shock wave. This means the terminator runs faster than the speed of sound, that is, the surface speed of the Earth's rotation exceeds the speed of sound, and we are rotating at supersonic speeds!

"The last star will slowly cool and fade away. With its passing, the Universe will become once more a void, without light or life or meaning."
So warned the physicist Brian Cox in the recent BBC series Universe. The fading of that last star will only be the beginning of an infinitely long, dark epoch. All matter will eventually be consumed by monstrous black holes, which in their turn will evaporate away into the dimmest glimmers of light. //

let's take a look at how "material" – physical matter – first came about. If we are aiming to explain the origins of stable matter made of atoms or molecules, there was certainly none of that around at the Big Bang – nor for hundreds of thousands of years afterwards.

Aurora Borealis, the good old.
Taken by Markus on November 15, 2021 @ Tromsø Norway

Stellarium is a free open source planetarium for your computer. It shows a realistic sky in 3D, just like what you see with the naked eye, binoculars or a telescope.

Try the Web Version

This is not an APODThese APODs are not real.
They were made with a score-based generative model.
Check out the paper for more info.
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The astronomical unit was defined to be exactly 149 597 870 700 meters in 2012, so it is no longer a measured value. In fact, it never was a measured value. It was instead a computed value, and it was computed rather strangely.

Prior to 2012, the astronomical unit was defined as the distance between the center of the Sun at which a tiny particle in an unperturbed circular orbit about the Sun would yield a value of exactly 0.0172020985 for the Gaussian gravitational constant. That value corresponds to the distance at which a tiny particle in an unperturbed circular orbit about the Sun would have an orbital angular velocity of 0.0172020985 radians per solar day. That value corresponds to an orbital period of 365.256898 days. That value, now called a Gaussian year, was based on measurements available to Gauss of the length of a sidereal year. (The currently accepted value of the sidereal year is 365.256363004 days of 86400 seconds each.)

This outdated value in the length of a sidereal year was one of the reasons the astronomical unit was given a defined value in 2012. There were other reasons. One is that that definition made the concept of the astronomical unit a bit (more than a bit?) counter-intuitive. With that definition, uncertainty in the computed value of astronomical unit depended on the ability of solar system astronomers to estimate the Sun's gravitational parameter (conceptually, the product of the Newtonian gravitational constant and the Sun's mass; in practice, a quantity that could be estimated directly as a consequence of models used to generate ephemerides) and the ability to measure time.

The ability to measure time (currently about one part in 1016
) has far outpaced the ability to estimate the Sun's gravitational parameter (currently less than one part in 1010). This means that if the 2012 change had not happened, the uncertainty in the astronomical unit would depend on the ability estimate the Sun's gravitational parameter, about three parts in 1011, or about 0.000000003%. That's a lot better than the 0.0000001% precision asked about in the question.

One of the most spectacular Einstein rings ever seen in space is enabling us to see what's happening in a galaxy almost at the dawn of time.
The smears of light called the Molten Ring, stretched out and warped by gravitational fields, are magnifications and duplications of a galaxy whose light has traveled a whopping 9.4 billion light-years. This magnification has given us a rare insight into the stellar 'baby boom' when the Universe was still in its infancy. //

The Molten Ring (formally named GAL-CLUS-022058s) is just such an Einstein ring, magnified by the gravitational field around a huge cluster of galaxies in the constellation of Fornax. So powerful is this effect that not only does the distant galaxy appear in four distorted images, it's magnified by a factor of 20.
When combined with the Hubble Space Telescope, the resulting images are as detailed and sharp as observations taken with a telescope with a huge 48-meter aperture. From this, a team of researchers led by Anastasio Díaz-Sánchez of the Universidad Politécnica de Cartagena in Spain worked out that light from the galaxy has traveled 9.4 billion light-years.

We don't even know everything we don't know – a fact that's been made evident in a new discovery. While running equations for quantum gravity corrections for the entropy of a black hole, a pair of physicists found that black holes exert pressure on the space around them.
Not much pressure, to be sure – but it's a finding that's fascinatingly consistent with Stephen Hawking's prediction that black holes emit radiation and therefore not only have a temperature, but slowly shrink over time, in the absence of accretion.
"Our finding that Schwarzschild black holes have a pressure as well as a temperature is even more exciting given that it was a total surprise," said physicist and astronomer Xavier Calmet of the University of Sussex in the UK.
"If you consider black holes within only general relativity, one can show that they have a singularity in their centres where the laws of physics as we know them must break down.
"It is hoped that when quantum field theory is incorporated into general relativity, we might be able to find a new description of black holes." //

the finding could have interesting implications for our attempts to square general relativity (on macro scales) with quantum mechanics (which operates on extremely small scales).
Black holes are thought to be key to this undertaking. The black hole singularity is mathematically described as a one-dimensional point of extremely high density, at which point general relativity breaks down – but the gravitational field around it can only be described relativistically.
Figuring out how the two regimes fit together could also help tp solve a really thorny black hole problem. According to general relativity, information that disappears beyond a black hole could be gone forever. Under quantum mechanics, it can't be. This is the black hole information paradox, and mathematically exploring the space-time around a black hole could help resolve it.

Gravity is the weird, mysterious glue that binds the Universe together, but that's not the limit of its charms. We can also leverage the way it warps space-time to see distant objects that would be otherwise much more difficult to make out.

This is called gravitational lensing, an effect predicted by Einstein, and it's beautifully illustrated in a new release from the Hubble Space Telescope.

In the center in the image (below) is a shiny, near-perfect ring with what appear to be four bright spots threaded along it, looping around two more points with a golden glow.

This is called an Einstein ring, and those bright dots are not six galaxies, but three: the two in the middle of the ring, and one quasar behind it, its light distorted and magnified as it passes through the gravitational field of the two foreground galaxies.

Because the mass of the two foreground galaxies is so high, this causes a gravitational curvature of space-time around the pair. Any light that then travels through this space-time follows this curvature and enters our telescopes smeared and distorted – but also magnified.

A potentially dangerous asteroid called Bennu has a 1 in 1,750 chance of hitting Earth between now and the year 2300.

That's according to the most precise calculations of an asteroid's trajectory ever made, and the odds are slightly worse than NASA previously thought.

Still, the researchers studying Bennu say this doesn't keep them up at night.

"The impact probability went up just a little bit but it's not a significant change," says Davide Farnocchia at the Center for Near Earth Object Studies at NASA's Jet Propulsion Laboratory in Southern California.

He points out that there is a 99.94% probability that Bennu is not on an impact trajectory.

A multibillion-dollar radio telescope is moving into its construction phase while still working to raise funding and deal with satellite megaconstellations whose interference “change the game” for their plans.

In a June 29 talk at the annual meeting of the European Astronomical Society, Philip Diamond, director general of the Square Kilometer Array (SKA) Observatory, announced that the observatory’s council had formally approval plans to move into the construction phase of the radio telescope.

SKA is two separate facilities. SKA-Low, in Western Australia, will eventually be an array of more than 130,000 antennas performing observations at low frequencies. SKA-Mid will feature 197 dishes in South Africa for midrange radio frequencies, including 64 dishes of the existing MeerKAT array there.

It is hard for humans to wrap their heads around the fact that there are galaxies so far away that the light coming from them can be warped in a way that they actually experience a type of time delay. But that is exactly what is happening with extreme forms of gravitational lensing, such as those that give us the beautiful images of Einstein rings. In fact, the time dilation around some of these galaxies can be so extreme that the light from a single event, such as a supernova, can actually show up on Earth at dramatically different times. That is exactly what a team led by Dr. Steven Rodney at the University of South Carolina and Dr. Gabriel Brammer of the University of Copenhagen has found. Except three copies of this supernova have already appeared – and the team thinks it will show up again one more time, 20 years from now.

Finding such a supernova is important not just for its mind bending qualities – it also helps to settle an important debate in the cosmological community. The rate of expansion of the universe has outpaced the rate expected when calculated from the cosmic microwave background radiation. Most commonly, this cosmological conundrum is solved by invoking “dark energy” – a shadowy force that is supposedly responsible for increasing the acceleration rate. But scientists don’t actually know what dark energy is, and to figure it out they need a better model of the physics of the early universe.

A stunning photo of the aurora over Siberia has been captured from a 747 cockpit by pilot Christiaan van Heijst.
Christiaan takes up the story.
“Completely unexpected this time of year: a fierce show of dancing northern lights while crossing the Siberian plains. What started as a dim green glow, barely visible to the naked eye, soon turned into a frenzy of bright lights with luminescent purple pillars that reached far into space.
“Curtains of rapidly moving light, powered by a powerful solar flare that traveled with the speed of light across the solar system. Particles that have been released from the Sun eight minutes before, caught in Earth’s magnetic field and showing up in ways words fail to describe.

Two black holes; one very warped tango.

Black Hole

First in a four-part exclusive Asia Times interview with renowned physicist and Big Bang theory critic Eric Lerner
By JONATHAN TENNENBAUM

The Big Bang is probably the most famous scientific theory since Einstein’s relativity. The Big Bang theory says that our Universe began with a gigantic explosion, about 14 billion years ago, and has been expanding and cooling down ever since.

Until relatively recently this theory has been regarded as the foundation of modern cosmology, the branch of science devoted to the study of the Universe as a whole.

But not all scientists agree with the Big Bang theory, and some even say it is completely wrong and contradicted by a growing mountain of evidence. In fact, in recent years one hears more and more talk about a “crisis of cosmology.”

I am talking now to one of the most well-known, outspoken critics of the Big Bang, the American physicist Eric J Lerner.

Scientists were expecting to find an intermediate-mass black hole at the heart of the globular cluster NGC 6397, but instead they found evidence of a concentration of smaller black holes lurking there. New data from the NASA/ESA Hubble Space Telescope have led to the first measurement of the extent of a collection of black holes in a core-collapsed globular cluster.

Just after sunset on Sunday, Jupiter, Saturn, and Mercury will have a rare triple conjunction, coming close together from our perspective. The trio will form a small, clear triangle low in the southwest sky with Jupiter sitting at the top of their planetary pyramid. The planets will actually be near each other each night from January 8 through January 11, but the tightest group will happen on January 10, per EarthSky. Though, you should look right away, because they won't stay above the horizon for long.

To settle the score, an international team of astronomers led by Cornell university used data from the National Science Foundation's Atacama Cosmology Telescope (ACT) in Chile and "cosmic geometry" to end the debate, Cornell officials said in a statement. Their estimate of (about) 13.77 billion years roughly matches the estimate from the Planck Collaboration.

"Now we've come up with an answer where Planck and ACT agree," astronomer Simone Aiola, a researcher at the Flatiron Institute's Center for Computational Astrophysics in New York City and author of one of two new papers describing these findings, said in the same statement. "It speaks to the fact that these difficult measurements are reliable."

By determining the age of the universe, the researchers also were able to estimate how fast the universe is expanding — this figure is known as the Hubble constant. With ACT, they calculated a Hubble constant of 42 miles per second per megaparsec, or 67.6 kilometers per second per megaparsec. In other (simpler) words, they found that an object 1 megaparsec (or about 3.26 million light-years) away from Earth would be moving away from Earth at 42 miles per second (67.6 km/s).