Stars Are At Different Places For New Horizons From Where We See Them On Earth

originally posted by: Soylent Green Is People
So the normal motion of the solar system will have more of an effect on the positions of stars than the motion of New Horizons over the years. However, even then the apparent star positions only change negligibly -- and in general imperceptibly without the use of measurement instruments -- over the span of a human lifetime.

It is nothing to do with the speed of the solar system, or that of the probe relative to the solar system. It is the distance apart of the earth and the probe.

The two pictures on the NASA site were taken at the same time as near as possible, and demonstrate parallax very nicely.
Even using the much smaller baseline of the earth's orbit, which is how parallax measurements are normally made, will show a shift of slightly under 1 arc second, and this method can be used out to about 300 ly.

And stars proper motions (movement in the sky) can be surprisingly large.

If you have Stellarium then check the values for Proxima Centauri. The proper motion is nearly 4 arc seconds per year.

originally posted by: Darkstar2

originally posted by: Soylent Green Is People
So the normal motion of the solar system will have more of an effect on the positions of stars than the motion of New Horizons over the years. However, even then the apparent star positions only change negligibly -- and in general imperceptibly without the use of measurement instruments -- over the span of a human lifetime.

It is nothing to do with the speed of the solar system, or that of the probe relative to the solar system. It is the distance apart of the earth and the probe.

The two pictures on the NASA site were taken at the same time as near as possible, and demonstrate parallax very nicely.
Even using the much smaller baseline of the earth's orbit, which is how parallax measurements are normally made, will show a shift of slightly under 1 arc second, and this method can be used out to about 300 ly.

My point is that the distance New Horizons is from Earth is about the same distance Earth (and the rest of the solar system) is right now compared to where earth was just one year ago. And (for example) over a span of 10 years the Earth/solar system today is much farther away from where the earth was just 10 years ago -- 10X farther compared to how far New Horizons is from Earth.

Over those 10 years, it is practically impossible to visually see (without measuring devices) any difference of the stars apparent locations over that time, even though the Earth/solar system is 44 Billion miles farther away from the point in space it was 10 years ago (and for comparison, New Horizons is about 1/10 that distance from Earth, or 4.3 Billion miles).

And stars proper motions (movement in the sky) can be surprisingly large.

If you have Stellarium then check the values for Proxima Centauri. The proper motion is nearly 4 arc seconds per year.

True. There are some high proper motion stars. That's why I said that "generally" the proper motions are indefectible by eye over a human lifetime. There are, as you said, notable exceptions, Barnard's Star being another. Barnard's star has moved a noticeable distance compared to other stars in a relatively short time. It's a bit to dim to see without a telescope, but if we could see it we would notice that it has moved compared to the stars around it in just a few decades.


However, I'm not doubting the ability to detect the apparent motion of stars over time. My point is that the differences from just the motion of the Earth/Solar system through the galaxy (i.e. where Earth is today compared to where Earth was just 5 or 10 years ago) makes for a greater difference in our viewpoint of the stars than does the location of where New horizons is compared to where Earth is.

We don't need to wait the 15 years it took for New Horizons to go the get 4.3 Billion miles away to see what the stars in the galaxy look like 4.3 billion miles from Earth. Earth itself will travel that far through the galaxy it just one year. Look at the sky now and then look at it a year from now; we'll be about that same 4.3 billion miles from here by then.

originally posted by: Soylent Green Is People
The Earth, sun, and the rest of the Solar system are moving through the galaxy at about 500,000 mph (800,000 kph). New Horizons at top speed was moving at 52,000 mph (83,000 kph) but has since slowed from that speed due to the sun trying to pull it back over the years.

For argument's sake (and for round numbers sake), let's say say New Horizons average speed since launch is 50,000 mph. That's still 10 times slower that the Earth/solar system is moving relative to galaxy.

So the normal motion of the solar system will have more of an effect on the positions of stars than the motion of New Horizons over the years. However, even then the apparent star positions only change negligibly -- and in general imperceptibly without the use of measurement instruments -- over the span of a human lifetime.

Let's say you're on a merry-go-round, and you want to get a different perspective of the other "horses".

So you get off your horse and walk 3 meters next to the edge of the merry-go-round. Now you can see the horses from a little different angle.

What your proposal "So the normal motion of the solar system will have more of an effect on the positions of stars than the motion of New Horizons over the years" sounds like to me is you just sit on your horse, and because the merry-go-round is moving, you will get a different perspective on the other horses because of that motion. OK not exactly because the stars in the galaxy aren't as fixed in position relative to each other as the horses on the merry-go-round. However, effectively from our vantage point in the milky way, the stars nearest to us, where parallax can be observed, are generally moving pretty much with us in rotation around the Milky way, so I think the motion we experience from the rotation of the Milky way is not very helpful for parallax measurements. See the rotation velocities of stars in the milky way at our distance of about 8.1 kpc from the galactic center:

Rotation curve of the Milky Way


Now maybe you're thinking, what about outside our galaxy? Parallax technology is always improving but for most of history since parallax was first used in stellar distance measurement in 1848, we've just been using it to measure the distance of stars in our own galaxy.

Maybe your idea could possibly help in parallax measurements of other galaxies, but if it's been used this way I haven't run across it. Other galaxies are very distant. Now if we waited for half a rotation around the galaxy, that's about 120 million years if the period of a full orbit is 240 million years. That would give us a long baseline. But it violates the rule in science that you like to be alive to see your experiment or measurement completed.

a reply to: Arbitrageur

I get it. But my tl;dr version of what I'm saying is simply that if you want to see what the stars look like 4.3 billion miles from where Earth is right now (e.g., from the location of New Horizons), then just wait a year and look up in the sky. In one year's time, Earth will be 4.3 billion miles from where we are right now.

The parallax between two images of the sky taken from Earth a year apart will be similar in magnitude to the current parallax between Earth and New Horizons.

originally posted by: Soylent Green Is People
a reply to: Arbitrageur

I get it.

No, I'm afraid you haven't grokked it yet, my friend.

The parallax between two images of the sky taken from Earth a year apart will be similar in magnitude to the current parallax between Earth and New Horizons.

Again, this is not true. Taking photos a year apart is like sitting on your horse on the merry-go-round and then later after the merry-go-round rotates, expecting to see a different view of the horses. You won't see a different view of the other horses, they are maintaining their positions relative to you. You have to actually send a "probe" or another person, to walk around on the merry go-round, to get a different view of the other horses, analogous to new horizons. So, the stars in our galaxy won't look much different due to a year of galactic rotation, especially not the stars in our region of the galaxy where parallax would be most pronounced, since their galactic orbital velocities match ours fairly closely though they may have other motion, suggested by the "noise" or variation above and below the average velocity line in the milky way orbital velocity graph in my previous post. Other galaxies are so distant that they won't look much different either.

The parallax between two images of the sky taken from Earth a 6 months apart gives us a baseline of the 186 million miles of the Earth's orbit, which is independent from the motion of the rest of the galaxy, so it's not like just sitting on the horse on the merry-go-round. But after 1 year the earth is back to approximately the same position with respect to the sun so the parallax versus a year ago is gone.

Here's a challenge for you if you still think it's true that "The parallax between two images of the sky taken from Earth a year apart will be similar in magnitude to the current parallax between Earth and New Horizons", surely if parallax opportunities present themselves, astronomers would make use of them, right? They used the New Horizons parallax. See if you can find any evidence of astronomers taking sky photos, then waiting a year for the galaxy to rotate, and then taking more sky photos to use the galactic rotation as a baseline. If they use that technique at all I would expect them to use it for parallax measurements to other galaxies, and not for other stars in our galaxy since in the merry-go-round analogy just sitting on the horse doesn't give you a different view of the other horses, even if the whole thing is rotating.

The other galaxies are so far away that even a long baseline from 1 year of galactic rotation would still require incredibly accurate angular measurements to use that kind of parallax, beyond our present capabilities.

Why can't astronomers use parallax to measure distances to other galaxies?

Parallax only works for relatively close stars in our own galaxy. Other galaxies are simply too far away.

There are some things we can do with galactic rotation effects, but I'm not going to go on that tangent now since it's not parallax, and until you understand the parallax issue I think it would just add more confusion.

a reply to: Arbitrageur


If the signals from a Very Long Base Interferometry reception are recombined at a very high frequency clock rate there might be some unexpected relativistic results. They spent a lot of money building the Michelson Morley interferometer on similar speculation.

More recently, in 2009, optical resonator experiments confirmed the absence of any aether wind at the 10−17 level.

We don't get to play with accurate clocks here on ATS but wouldn't be quite a year..

a reply to: Arbitrageur

Ah...Makes sense. Thanks!

a reply to: Soylent Green Is People

Still isn't clear what the reference point is.

I like your first step determining

where earth was just one year ago.

We can look at galactic and solar system relative motions later.

The Earth's orbit is an Ellipse closer to the sun some times than at others.
To simplify things we could think of the Earth rotating around the sun in a perfect circle, every day the angle change from the center of the sun to the Earth's core position would be about 3602.38882190719 arc seconds.

But more recently in 2021 they claim the Earth is spinning faster and that we may no longer need to add a leap second at the end of the year to be in the same place?

If this is entirely due to a local Earth spin phenomena then at the end of the year the star reference we use will align a second earlier. It would be like playing billiards and marking the ball at a tiny fraction of a different angle rather than the center of the ball being accurately located.

So Earth centered analysis is indeterminate even at just one year relative to the sun.

In Stranger in a Strange Land grok meant "to drink".
Potentially polar ice melt or earth core modes could cause the faster spin but there is no perfect answer.

www.space.com...

a reply to: Slichter

Actually for a perfect circular orbit I think the daily change in angle should be 3548.3303955462420163 arc seconds for an average year length of 365.2422 days.

Earth spin rate will not affect the orbit of the earth.

I haven't seen any analysis of why this change of spin rate happened, but I know that one of the affecting items are earthquakes.

If the earthquake involves a large mass and a large (relatively) displacement then the law of angular momentum conservation will change the length of the day by a (very) small amount.

Orbit changes are mostly down to perturbations from other planets, mostly Jupiter and Saturn.

a reply to: Slichter
Your link says the earth's spin is slowing down, over time, which is true,but it's not a steady decline, which is also true, so there are some bumps in the slowing down trend. So a leap second added in 2016 may have to be temporarily removed, but, no doubt it will be added back. Days used to be 23 hours long, and in the future they will be 25 hours long so the overall trend is for slower rotation. It's interesting to see bumps in the decline though.

originally posted by: Darkstar2
Earth spin rate will not affect the orbit of the earth.

I haven't seen any analysis of why this change of spin rate happened, but I know that one of the affecting items are earthquakes.

Yes, earthquakes can do it. Slichter's link mentions other possible factors which can affect earths rotation rate. There's a long term trend for Earth's orbit to get larger, mainly because the sun is losing mass every day as it converts hydrogen to helium, but since the orbit only gets bigger by 1.5 cm each year, most people will never notice, after all what's 1.5 cm compared to the distance from the Earth to the sun? But over time it adds up. One prediction is that when the sun turns into a red giant, it may expand as far as Earth's current orbit, but Earth may not get swallowed by the sun since its orbit will be significantly larger by then, billions of years from now. Those predictions have pretty big error bars though, so I don't think we know exactly how large the sun will get when it's dying.

a reply to: Arbitrageur

Milankovitch cycles describe the collective effects of changes in the Earth's movements on its climate over thousands of years.

en.wikipedia.org...

This is likely where physicists like Hawking were Groking and others were looking for solid mathematically robust predictive modeling.

The New Horizons observations could refine future predictions for our solar system in the million+ year range.
The video doesn't lead us anywhere really other than to suggest that there was a surprise(for some physicists) that didn't match current theory predictions? I guess to stay on topic we would need to know who was groking and if there really is some new objective paradigm that should be embraced.