Author Topic: Astronomy Thread  (Read 121175 times)

Offline Star One

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Re: Astronomy Thread
« Reply #700 on: 03/18/2019 06:51 am »
US detects huge meteor explosion

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A huge fireball exploded in the Earth's atmosphere in December, according to Nasa.

The blast was the second largest of its kind in 30 years, and the biggest since the fireball over Chelyabinsk in Russia six years ago.

But it went largely unnoticed until now because it blew up over the Bering Sea, off Russia's Kamchatka Peninsula.

The space rock exploded with 10 times the energy released by the Hiroshima atomic bomb.

Lindley Johnson, planetary defence officer at Nasa, told BBC News a fireball this big is only expected about two or three times every 100 years.


Offline bkellysky

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Re: Astronomy Thread
« Reply #701 on: 03/18/2019 04:26 pm »
This is way too technical for me to express an opinion.

Venus is not Earth’s closest neighbor

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Calculations and simulations confirm that on average, Mercury is the nearest planet to Earth—and to every other planet in the solar system.

I was surprised to learn in Sky and Telescope a few years ago that Mercury was most often the closest planet to Earth.  There is so much fuss about Martian close approaches and I knew Venus comes the closest of all the planets to Earth.  Because Mercury does not get too far from Earth, it is most frequently the closest planet to Earth.

I plotted a graph of distance from Earth to Mercury, Venus and Mars for two years centered on this month, attached here and at my blog at https://bkellysky.wordpress.com/2019/03/18/which-planet-is-closest-to-earth-most-often/

Offline eeergo

Re: Astronomy Thread
« Reply #702 on: 03/18/2019 11:46 pm »
I was surprised to learn in Sky and Telescope a few years ago that Mercury was most often the closest planet to Earth.  There is so much fuss about Martian close approaches and I knew Venus comes the closest of all the planets to Earth.  Because Mercury does not get too far from Earth, it is most frequently the closest planet to Earth.

I plotted a graph of distance from Earth to Mercury, Venus and Mars for two years centered on this month, attached here and at my blog at https://bkellysky.wordpress.com/2019/03/18/which-planet-is-closest-to-earth-most-often/

But that's the thing, it's a trivial result that for any given planet, any circularly-orbiting object arbitrarily close to its star (with the limit being the star around which the planet under consideration orbits) will be closest to it on average.

You can even see it intuitively: as you plotted, the sinusoidals will start getting flatter and flatter until you reach a flat constant line (the system's star), while any other circularly-orbiting object farther from the star will be closer at some point of its orbit, but also diametrically-opposite the star at some other moment, increasing the average distance for at least half of its orbit. Unless you're considering something in the planet-star Lagrange points, this is the case for a suitably long time period (to account for close-coorbiting bodies) for any planet, star and distance considered, provided it's a circular orbit as the article considers.

The farther the considered planet orbits, the clearer this effect gets - hence why Mercury is the closest planet, on average, to *any* of the Solar System's planets, and even to Pluto whose results gets a bit more complicated due to eccentricity and plane inclination issues.
-DaviD-

Online ugordan

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Re: Astronomy Thread
« Reply #703 on: 03/19/2019 03:20 pm »
US detects huge meteor explosion

Scott Manley has a Himawari image sequence in his new video:

Offline Star One

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Astronomy Thread
« Reply #704 on: 03/19/2019 07:06 pm »
Talking longer term I think there is a possibility that the Earth will see an uptick in impacts over the next million years as I was reading an article in Astronomy Now January 2019 issue that there is a theory that Gaia data will show that Scholz’s Star went further into the Oort Cloud 70,000 years ago than initial calculations showed. That the information to prove or disprove this theory will be in the next Gaia data release.
« Last Edit: 03/19/2019 07:08 pm by Star One »

Online Rondaz

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Re: Astronomy Thread
« Reply #705 on: 03/20/2019 08:19 pm »
Dancing the Lunar Transit

By Sarah Frazier NASA’s Goddard Space Flight Center
March 20, 2019

On March 6, 2019, our Solar Dynamics Observatory, or SDO, witnessed a lunar transit — where both the Sun and Moon displayed a little odd behavior.

First, there was the transit itself. A lunar transit occurs when the Moon passes between SDO and the Sun, blocking the satellite’s view. But instead of appearing on one side of the frame and disappearing on the other, the Moon seemed to pause and double back partway through crossing the Sun. No, the Moon didn’t suddenly change directions in space: This is an optical illusion, a trick of perspective.

Here’s how it happened: SDO is in orbit around Earth. When the transit started, the satellite was moving crosswise between the Sun and Earth, nearly perpendicular to the line between them, faster than the Moon. But during the transit, SDO started the dusk phase of its orbit — when it’s traveling around towards the night side of Earth, moving almost directly away from the Sun — but no longer making any progress horizontally to the Sun. The Moon, however, continued to move perpendicular to the Sun and thus could “overtake” SDO. From SDO’s perspective, the Moon appeared to move in the opposite direction.

The second, subtler part of this celestial dance seemed to come from the Sun itself. If you look closely, you may notice the Sun seems to wiggle a bit, side-to-side and up and down, during the transit. That’s another result of SDO’s perspective, though in a different way.

SDO relies on solar limb sensors to keep its view steady and focused on the Sun. These limb sensors consist of four light sensors arranged in a square. To keep the Sun exactly centered in its telescopes, SDO is trained to move as needed to keep all four sensors measuring the same amount of light.

But when the Moon covers part of the Sun, the amount of light measured by some of the sensors drops. This makes SDO think it’s not pointed directly at the Sun, which would cause SDO to repoint — unless that function gets overridden.

Since SDO’s fine guidance system wouldn’t be much use during a lunar transit regardless, the mission team commands the spacecraft to disregard limb sensor data at the beginning of such transits. This loss of fine guidance accounts for some of the Sun’s apparent movement: SDO is now pointing at a general Sun-ward spot in space, instead of keeping its view steady using the much more accurate limb sensors.

The other factor behind the apparently wiggly Sun is temperature. SDO’s instruments are designed to work in the full glare of the Sun’s light and heat. When the Moon’s shadow passes over the spacecraft, the instruments quickly cool in the vacuum of space and start to bend and flex. The flexing of the front part of the telescope can make it look like the image is moving around in the frame.

SDO’s operators use strategically-placed heaters onboard the spacecraft to minimize this flexing as much as possible and to get back to providing science-quality data — images that are focused, centered and steady — as quickly as possible.

https://blogs.nasa.gov/sunspot/2019/03/20/dancing-the-lunar-transit/

Offline Star One

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Re: Astronomy Thread
« Reply #706 on: 03/22/2019 06:44 am »
Astronomers find 83 quasars already shining in early universe

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Astronomers studying some of the most ancient light in the cosmos have found 83 ancient quasars in a field where only 17 were previously known, an indication that supermassive black holes must have been relatively common in the extremely early universe. The discovery, using the Hyper Suprime-Cam wide field camera mounted on the Subaru Telescope, required 300 nights of observation time over five years.

Offline Star One

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Astronomy Thread
« Reply #707 on: 03/22/2019 04:30 pm »
Best-Yet Measurements Deepen Cosmological Crisis

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A long-running dispute about how fast our universe is expanding just became even more entrenched. New and more precise measurements of stars in the Large Magellanic Cloud, a satellite galaxy of the Milky Way, have only strengthened the differences between two independent methods of calculating the expansion rate.
This impasse may soon force cosmologists to reexamine the “standard model” of cosmology, which tells us about the composition of the universe (radiation, normal matter, dark matter and dark energy) and how it has evolved over time.

Referring to the above article something is clearly wrong and it looks to be the standard model.

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Scientists have announced the observation of “CP violation in a D0 meson” at CERN, a discovery that will appear in physics textbooks for years to come. You’re probably wondering what exactly it means.

The Universe is full of regular matter. There’s also antimatter, which exists even here on Earth, but there’s much less of it. This new observation is important on its own, but it also takes physicists another step closer to explaining where all the antimatter has disappeared to.

https://gizmodo.com/why-an-incredible-new-cern-observation-has-physicists-p-1833466787
« Last Edit: 03/22/2019 04:56 pm by Star One »

Offline Star One

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Re: Astronomy Thread
« Reply #708 on: 03/22/2019 08:15 pm »
NASA Instruments Image Fireball over Bering Sea

On Dec. 18, 2018, a large "fireball" - the term used for exceptionally bright meteors that are visible over a wide area - exploded about 16 miles (26 kilometers) above the Bering Sea. The explosion unleashed an estimated 173 kilotons of energy, or more than 10 times the energy of the atomic bomb blast over Hiroshima during World War II.

Two NASA instruments aboard the Terra satellite captured images of the remnants of the large meteor. The image sequence shows views from five of nine cameras on the Multi-angle Imaging SpectroRadiometer (MISR) instrument taken at 23:55 Coordinated Universal Time (UTC), a few minutes after the event. The shadow of the meteor's trail through Earth's atmosphere, cast on the cloud tops and elongated by the low sun angle, is to the northwest. The orange-tinted cloud that the fireball left behind by super-heating the air it passed through can be seen below and to the right of the GIF's center.

The still image, captured by the Moderate Resolution Imaging SpectroRadiometer (MODIS) instrument, is a true-color image showing the remnants of the meteor's passage, seen as a dark shadow cast on thick, white clouds. MODIS captured the image at 23:50 UTC.

The Dec. 18 fireball was the most powerful meteor to be observed since 2013; however, given its altitude and the remote area over which it occurred, the object posed no threat to anyone on the ground. Fireball events are actually fairly common and are recorded in the NASA Center for Near Earth Object Studies database.

The Terra spacecraft was launched in 1999 and is managed by NASA's Goddard Space Flight Center in Greenbelt, Maryland. The MISR instrument was built and is managed by NASA's Jet Propulsion Laboratory in Pasadena, California, for NASA's Science Mission Directorate in Washington. JPL is a division of Caltech. The MISR data were obtained from the NASA Langley Research Center Atmospheric Science Data Center in Hampton, Virginia. The MODIS instrument is managed by NASA's Goddard Space Flight Center.

More information about MISR and MODIS is available at the following site(s):

https://www-misr.jpl.nasa.gov/

https://terra.nasa.gov/about/terra-instruments/modis


Offline edzieba

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Re: Astronomy Thread
« Reply #709 on: 03/25/2019 04:19 pm »
I don't need to develop a model calculating the coordinates of the North Pole relative to asteroid Itokawa during a million years to know that model doesn't describe anything generally useful.
Replace 'North Pole' with 'Nagano Prefecture', you have a useful tool for signal strength between Usuda ground station and Hayabusa. Plenty of "that's dumb / it's so obvious / everyone knows that / why would anyone ever bother to calculate that?!" research turns out to be useful.
For Mercury being the average closest planetary body to all other planetary bodies (and most minor planets sharing the same plane) it may mean that designs for a system-side data relay network may have a reason to place a node in Mercury orbit (or somewhere nice and shielded like a shadow-skirting Lissajous around Mercury-Sun L2).

Offline eeergo

Re: Astronomy Thread
« Reply #710 on: 03/25/2019 06:18 pm »
I don't need to develop a model calculating the coordinates of the North Pole relative to asteroid Itokawa during a million years to know that model doesn't describe anything generally useful.
Replace 'North Pole' with 'Nagano Prefecture', you have a useful tool for signal strength between Usuda ground station and Hayabusa. Plenty of "that's dumb / it's so obvious / everyone knows that / why would anyone ever bother to calculate that?!" research turns out to be useful.

No, because the analytical "method" they used only works for circular orbits (Itokawa's e=0.3) and considers point-like objects.

My comment was a hyperbole, and furthermore you decontextualized it from the intended meaning, i.e. I don't need to create another unuseful model to understand theirs is.

There still are analytical exact formulas, not too complicated to derive even if cumbersome, to get that distance. Discovered hundreds of years ago. Using standard trigonometry. Could even add a phase for Earth's rotation and account for day/night cutouts.

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For Mercury being the average closest planetary body to all other planetary bodies (and most minor planets sharing the same plane) it may mean that designs for a system-side data relay network may have a reason to place a node in Mercury orbit (or somewhere nice and shielded like a shadow-skirting Lissajous around Mercury-Sun L2).

Mercury would only make the slightest bit of sense if used as a shade as you mention - otherwise you can just use any orbit close to the Sun for minimizing average distance to other circularly-orbiting bodies.

Although I would argue you'd be more interested in minimizing the r^2 losses for smaller periods (or just using several relays) rather than having huge losses all the time which, funny fact, turn out to be smaller on a "yearly" average, when that "year" might last hundreds of Earth years. The Sun would still be in the middle for a significant portion of the orbit.
-DaviD-

Offline Star One

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Re: Astronomy Thread
« Reply #711 on: 03/25/2019 08:35 pm »
Jupiter's unknown journey through the early solar system revealed

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The results show that Jupiter was formed four times further from the sun than its current position would indicate. "This is the first time we have proof that Jupiter was formed a long way from the sun and then migrated to its current orbit. We found evidence of the migration in the Trojan asteroids orbiting close to Jupiter," explains Simona Pirani, doctoral student in astronomy at Lund University, and the lead author of the study.

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The authors of the study also suggest that the gas giant Saturn and the ice giants Uranus and Neptune could have migrated in a similar way.

Offline Star One

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Astronomy Thread
« Reply #712 on: 03/25/2019 08:51 pm »
And this week’s way out physics theory is there is no reality only information. I looked up his new book and that sounds like some light bedtime reading...

Physics Is Pointing Inexorably to Mind

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In his 2014 book, Our Mathematical Universe, physicist Max Tegmark boldly claims that “protons, atoms, molecules, cells and stars” are all redundant “baggage.” Only the mathematical apparatus used to describe the behavior of matter is supposedly real, not matter itself. For Tegmark, the universe is a “set of abstract entities with relations between them,” which “can be described in a baggage-independent way”—i.e., without matter. He attributes existence solely to descriptions, while incongruously denying the very thing that is described in the first place. Matter is done away with and only information itself is taken to be ultimately real.
This abstract notion, called information realism is philosophical in character, but it has been associated with physics from its very inception. Most famously, information realism is a popular philosophical underpinning for digital physics. The motivation for this association is not hard to fathom.
« Last Edit: 03/25/2019 09:20 pm by Star One »

Offline CuddlyRocket

Re: Astronomy Thread
« Reply #713 on: 03/26/2019 05:19 pm »
And this week’s way out physics theory is there is no reality only information.

It would be more accurate to describe the theory as saying that the only reality is information.

Offline Star One

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Re: Astronomy Thread
« Reply #714 on: 03/26/2019 09:19 pm »
And this week’s way out physics theory is there is no reality only information.

It would be more accurate to describe the theory as saying that the only reality is information.

You are quite correct that’s a more accurate description than mine.

Offline Star One

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Re: Astronomy Thread
« Reply #715 on: 03/28/2019 07:33 pm »
NASA's Hubble nabs spectacular image of asteroid coming apart

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Because of constant pressure from the sun, a space rock beyond Mars is spinning so much that it's literally cracking up.

Offline Star One

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Re: Astronomy Thread
« Reply #716 on: 03/28/2019 08:02 pm »
Persistence of intense, climate-driven runoff late in Mars history

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Mars is dry today, but numerous precipitation-fed paleo-rivers are found across the planet’s surface. These rivers’ existence is a challenge to models of planetary climate evolution. We report results indicating that, for a given catchment area, rivers on Mars were wider than rivers on Earth today. We use the scale (width and wavelength) of Mars paleo-rivers as a proxy for past runoff production. Using multiple methods, we infer that intense runoff production of >(3–20) kg/m2 per day persisted until <3 billion years (Ga) ago and probably <1 Ga ago, and was globally distributed. Therefore, the intense runoff production inferred from the results of the Mars Science Laboratory rover was not a short-lived or local anomaly. Rather, precipitation-fed runoff production was globally distributed, was intense, and persisted intermittently over >1 Ga. Our improved history of Mars’ river runoff places new constraints on the unknown mechanism that caused wet climates on Mars.

Offline Star One

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Re: Astronomy Thread
« Reply #717 on: 03/29/2019 12:40 pm »
Debunking this nonsense story.

Here's The Truth About That Photo of 'Mushrooms' Growing on Mars

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A peculiar new paper, published in a little-known scientific journal, has the tabloids stirred up about the possibility of life on Mars.

According to this paper, an international team of scientists are now claiming to have found evidence of 'mushrooms' growing on the surface of the Red Planet.

The 'evidence' is primarily based on images, taken by NASA's Curiosity and Opportunity rovers, which capture a birds-eye-view of what look like, well, mushrooms.

Offline Star One

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Astronomy Thread
« Reply #718 on: 03/29/2019 08:31 pm »
Astronomers discover mysterious star displaying never-seen-before behaviour

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Many, if not most, stars vary in brightness, typically by just a little and very predictably. These changes occur on timescales from minutes to years, and can tell us about the internal structure of stars in a way that no other observations can. But recently, a team of astronomers used ESO facilities to discover an extreme variable star named VVV-WIT-07, with WIT being short for “What is this?”. Seen from Earth, this strange star suddenly and irregularly reduces in brightness by 30–40%. In one extraordinary case it even dimmed by about 80%. But “normal” stars just don’t do that. The research was led by Roberto Saito from the Universidade Federal de Santa Catarina. ESO astronomer Valentin Ivanov was involved in the research and tells us more.

Interesting title on the paper.

https://arxiv.org/pdf/1811.02265.pdf
« Last Edit: 03/29/2019 08:36 pm by Star One »

Offline Star One

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Astronomy Thread
« Reply #719 on: 03/30/2019 09:59 am »
GRAVITY instrument breaks new ground in exoplanet imaging

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The GRAVITY instrument on ESO’s Very Large Telescope Interferometer (VLTI) has made the first direct observation of an exoplanet using optical interferometry. This method revealed a complex exoplanetary atmosphere with clouds of iron and silicates swirling in a planet-wide storm. The technique presents unique possibilities for characterising many of the exoplanets known today.

New evidence of deep groundwater on Mars

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In mid-2018, researchers supported by the Italian Space Agency detected the presence of a deep-water lake on Mars under its south polar ice caps. Now, researchers at the USC Arid Climate and Water Research Center (AWARE) have published a study that suggests deep groundwater could still be active on Mars and could originate surface streams in some near-equatorial areas on Mars.

The researchers at USC have determined that groundwater likely exists in a broader geographical area than just the poles of Mars and that there is an active system, as deep as 750 meters, from which groundwater comes to the surface through cracks in the specific craters they analyzed.
« Last Edit: 03/30/2019 10:26 am by Star One »