Posted by andsoitis 1 day ago
I'm sad not alive at a time like Cowboy Bebop oh well, this is a great pic, overview effect
> Artemis II crew take 'spectacular' image of Earth
It was described by someone else as spectacular - in this case NASA
> Artemis II crew take spectacular image of Earth
We the BBC certify that this image is officially spectacular
Not hugely important in this context. By more import, when the sentence is something like X 'commits warcrimes' against Y
I remember there's some tools to use the images as desktop backgrounds: https://github.com/boramalper/himawaripy
> We need to do a better job of preserving it.
Finally: Yes, global warming is real, but the threat is different. I predict that we will far exceed the average increase in global average temperature, but we will survive. Yes, we will survive, but with some "scars".
The exif includes time, but not time zone. They are not quite at the moon, and Lunar Time is under active development but not official. Also clocks tick slower under the moon's weaker gravity. (Or is it faster?)
Anyway, what time was this taken?
> clocks tick slower under the moon's weaker gravity. (Or is it faster?)
Compared to clocks at rest on Earth, clocks on board Orion right now are ticking faster, because it's at a high enough altitude above the Earth that the faster ticking due to higher altitude outweighs the slower ticking due to speed relative to the Earth.
That will be true for most of the mission. For clocks in orbit about the Earth, the "breakeven point" where the altitude effect and the speed effect cancel out and the clock ticks at the same rate as an Earth clock is at, IIRC, about 1.5 Earth radii. So clocks on the ISS, for example, tick slower than Earth clocks; but clocks on the GPS satellites (orbiting at 4.2 Earth radii) tick faster (and there is an adjustment made for this on each satellite so that the time signals they send out match Earth clock rates).
For a spacecraft moving at escape velocity, which is going to be roughly true for Orion all the way until splashdown, I think the "breakeven point" is higher, at a little over 2 Earth radii. Orion will reach that point on the way back a few hours before splashdown, I think.
The Moon's gravity well is too shallow to make an appreciable difference in any of these calculations.
I should emphasize that all these tick rate effects are tiny, on the order of one part in a billion to one part in a hundred billion. Even when you add up the difference over the entire mission, it's still only on the order of hundreds of microseconds (i.e., the astronauts end up aging a few hundred microseconds more than people who stayed on Earth).
I'm curious, and hope you or somebody else might be able to answer this: is it a single adjustment for each thing, where they just set it to always adjust by X ratio, or does it vary (enough to matter) as it orbits, such that the adjustment needs to be constantly varying slightly?
For the GPS satellites, their time signals are constantly compared with ground clocks, and adjustment signals are sent up to the satellites as needed to keep their clock corrections in sync with ground clocks.
I'm not sure what, if any, adjustments are made to clocks on the ISS, or how they're done.
https://www.nesdis.noaa.gov/imagery/satellite-maps
For reasons that are unexplainable if you're the NYTimes, polluting industries have been trying to kill these missions for decades.
I guess the rich person who was just planning to respond to my request needs to find another thing to spend their money on :)
They mean outside of low Earth orbit (which basically means further away than the ISS). The phrasing is not ideal.
> Earth's gravitational dominance extends 4x the distance to the moon
"Earth's gravitational dominance" is not a single thing; it depends on what kind of "dominance" you're talking about.
For example, even though the Moon is usually described as being in orbit about the Earth, its orbit is always concave towards the Sun. In other words, its net gravitational acceleration is always towards the Sun--even when the Earth is on the other side of it from the Sun. So by this criterion it's not in orbit about the Earth, it's in orbit about the Sun, doing a complicated do-si-do with the Earth, also in orbit about the Sun.
I'm not sure what definition of "dominance" you're using that extends the Earth's "dominance" to 4 times the distance of the Moon.
It’s about the suns gravitational pull on the moon dominating over the Earths gravitational pull on the moon, but that due to the centrifugal force (there isn’t one, so conservation of angular momentum) the Earth's gravitational pull dominates.
The claim about centrifugal force refers to the Hill sphere, which is a different notion of "gravitational dominance". The basic idea behind that is that, while the Sun's force on the Moon is greater than the Earth's, it varies in space, in the region where the Earth and Moon are orbiting, much less than the Earth's does. So we can "subtract out" the Sun's gravitational force, so to speak, since we can approximate it as constant in the region we're interested in.
The video, however, bungles this somewhat, because its claim about "centrifugal force" is made in a frame which is centered on the Sun--but rotating at the same rate the Earth revolves around the Sun. But nobody actually uses such a frame! Doing that would be silly. The natural frame for us on Earth to use if we "subtract out" the Sun's gravitational force to analyze the Earth-Moon motion is a frame centered on the Earth.
In this frame, we can say that the Moon orbits the Earth, not because there is some "centrifugal force" canceling out the Sun's force, but because we've subtracted out the Sun's force by centering our frame on the Earth. Or, to put it another way, we're treating the whole Earth-Moon system as freely falling in the Sun's gravitational field, and as long as the Sun's field is, to a good enough approximation, constant in the region we're interested in, we can simply ignore the Sun's gravitational force. (This viewpoint is much more natural in General Relativity, where "gravity" is not a force at all to begin with.) Such a frame is called an "Earth-Centered Inertial" frame, and it's the frame that's being used, for example, to manage the Artemis II spaceflight.