Ultimate space simulation software

 
A-L-E-X
Star Engineer
Star Engineer
Posts: 2139
Joined: 06 Mar 2017

Astrophotography

17 Aug 2020 06:53

Watsisname wrote:
A-L-E-X wrote:
Source of the post Here is what was really unusual- they seemed really low, maybe only a couple of hundred feet above the trees

Your eyes deceive you. :) You were seeing them at more like a couple hundred thousand feet.

People often misjudge how far away meteors are, thinking they are "just over those trees", or must have landed "just over that hill". But no. Meteors burn up several times higher than airplanes fly. Especially Perseids, which are typically small and come in so fast that they burn up very quickly in the upper atmosphere.

Larger meteors that reach lower altitudes or drop fragments on the ground (also usually of asteroid origin unrelated to a meteor shower) are also not visible so close to the surface. They slow down significantly and enter "dark flight", no longer draped by glowing plasma.  And if you *do* see a meteor reach just 100s of meters altitude and is still burning bright, then you're probably about to be killed by it and the impact will make global news.

Haha, I was even ducking and a little scared to be honest.  I stayed outside for an hour, but I admit I wish I had brought a helmet to protect my head (though I know that would have done no good.)
On DPR someone named "Jack" captured a picture of the kind of color I saw, so maybe these multicolored meteors aren't so rare?  He also said that they can make sounds as they heat the surrounding air?
The picture he posted here is very similar to what I saw:
https://www.dpreview.com/forums/post/64259642
 
A-L-E-X
Star Engineer
Star Engineer
Posts: 2139
Joined: 06 Mar 2017

Astrophotography

17 Aug 2020 06:59

midtskogen wrote:
Watsisname wrote:
Source of the post People often misjudge how far away meteors are, thinking they are "just over those trees", or must have landed "just over that hill". But no. Meteors burn up several times higher than airplanes fly. Especially Perseids, which are typically small and come in so fast that they burn up very quickly in the upper atmosphere.

Very true.  I receive a lot of reports about meteors, and very frequently people insist that they saw it land just behind that small hill a few hundred meters away, or even just behind the neighbour's house.  In those cases I can safely know that in reality they fell several 100 km away, since they saw it very low in the sky.  If it really falls nearby, it's always visible very high in the sky.  If it's heading for you, it will appear fairly high in the sky and travel slowly and straight up.  In fact, I recorded just such a meteor a couple of weeks ago.  This is what it looks like:

Meteor heading straight towards you

Since it was also recorded from other directions, the bright path is known, and even the dark path could be modelled based on this and wind data.  This was a fairly small object with an entry mass of a few kg most likely and an entry speed of about 15 km/s (dropping to just a couple at the end of the bright path at nearly 30 km altitude), so not many fragments have survived, most or all probably smaller than 100g, but the model shows them landing 3 to 6 km from here.  The debris field pretty extends pretty much straight over my house.

The way I was trying to judge distance is nearby trees and my house which was about a hundred yards in front of me.  I saw some meteors that were dim and very high and then these really bright ones which seemed much closer, and that multicolored one I mentioned that seemed to explode above and in front of me and that sound I heard that sounded like a pebble hitting a hard surface.
When you mentioned debris field, were you able to find any fragments?  Is there any way to distinguish them from terrestrial rocks or pebbles?  Also, if a meteor is headed straight for you, it will travel slowly and straight up?  I think you mean straight down (not sure about that.)
 
User avatar
midtskogen
World Builder
World Builder
Posts: 1032
Joined: 11 Dec 2016
Location: Oslo, Norway
Contact:

Astrophotography

17 Aug 2020 07:58

A-L-E-X wrote:
Source of the post When you mentioned debris field, were you able to find any fragments?

No.  I have look at the area to see what it looks like.  The easiest terrain in the field looks like this:
► Show Spoiler

Elsewhere, there is even more vegetation.  For small falls like this, a search is not worthwhile.  It's practically impossible to find something.  There could be 5 rocks weighing around 50g each and the search area is several square kilometers.  Had it been on a frozen lake, then there would actually be hope.


A-L-E-X wrote:
Source of the post  Is there any way to distinguish them from terrestrial rocks or pebbles?

Absolutely.  Usually what you need to look for is a dark rock which appears to be in a position where it doesn't seem to belong.  Unless it has cracked open (in which case the interior will be lighter), the surface is mostly smooth with dents looking like thumbprints.  The interior will offer final proof.


A-L-E-X wrote:
Source of the post Also, if a meteor is headed straight for you, it will travel slowly and straight up?  I think you mean straight down (not sure about that.)

No, it will indeed travel slowly and straight up, like in the video, and it will be fairly high in the sky.  Only if it appears straight overhead, it might travel slightly down (but that would be hard to tell anyway).  It's extremely unlikely that something will hit you, but I would go under a roof or tree and listen if I saw a big fireball travel straight up pretty high in the sky.  It will take a few minutes for the rocks to reach ground.

So, if you see a meteor falling down, you can be absolutely sure that it falls down a long way from you.  And the lower in the sky, the further away.  Or put another way: The closer it appears to fall, the further away it is in reality.

If you see it high in the sky, remember to wait for a while and listen for booms.  It will typically take 1.5 to a few minutes.  And it needs to be pretty bright, much brighter than Venus, but not necessarily as bright as the full moon.  In the video the brightness seems to have reached about -8 magnitude, and a series of booms was indeed heard, not very loud though.
NIL DIFFICILE VOLENTI
 
A-L-E-X
Star Engineer
Star Engineer
Posts: 2139
Joined: 06 Mar 2017

Astrophotography

17 Aug 2020 08:25

I got an excellent visual from your words!  Do you remember the fall in Siberia that occurred a few years ago?  I think that followed your pattern of seeing it high in the sky first and hearing the boom later.  The ones I saw must've been at least 50 km to 80 km away from me and probably never made it to the ground?  The terrestrial cues were fooling me lol.  The only thing I cant explain is that weird sound I heard like a falling pebble hitting the ground and I heard that sound right after the bright flash happened and it was no longer visible, I only heard that with one of them though, the multicolored one that had a very bright flash at the end, and that one was brighter than Venus by a significant amount but definitely not as bright as the full moon.

I remember reading that tektites were discovered in Antarctica because they really stood out in the bright white snow.  There were some lunar rocks and even a weird rock from Mars that was discovered there!
 
User avatar
midtskogen
World Builder
World Builder
Posts: 1032
Joined: 11 Dec 2016
Location: Oslo, Norway
Contact:

Astrophotography

17 Aug 2020 08:38

Meteorite dropping meteors are luminous down to 20 - 35 km altitude, typically, and shortly after that they lose all their cosmic (pre-entry) speed and the rocks will simply fall down as if dropped from an airplane, which will take at least a couple of minutes.  People who notice meteorites hitting the ground and pick them up, report that they're lukewarm.
NIL DIFFICILE VOLENTI
 
A-L-E-X
Star Engineer
Star Engineer
Posts: 2139
Joined: 06 Mar 2017

Astrophotography

17 Aug 2020 09:01

midtskogen wrote:
Meteorite dropping meteors are luminous down to 20 - 35 km altitude, typically, and shortly after that they lose all their cosmic (pre-entry) speed and the rocks will simply fall down as if dropped from an airplane, which will take at least a couple of minutes.  People who notice meteorites hitting the ground and pick them up, report that they're lukewarm.

Oh so if I want to narrow down the altitude range of what I saw, it would probably be somewhere between 20-35 km?  It was green, then yellow, then orange, and then a bright red and then there was a bright flash and then it was gone (and a split second after that I heard the pebble hitting a hard surface noise.)  I was facing West and it went from the Northwest to the West and that's where it disappeared (seemingly behind the trees and my house).  If the horizon is considered 0 degrees and the zenith is considered 90 degrees, it was approximately 30 degrees up when it disappeared.  I wonder if parts of it landed hundreds of yards away and I heard that?  Or if the sound was too soon after the bright flash to be that, maybe I heard the sound of the air heating up (or the meteor breaking up into smaller fragments mid air)?
 
User avatar
Watsisname
Science Officer
Science Officer
Posts: 1963
Joined: 06 Sep 2016
Location: Bellingham, WA

Astrophotography

17 Aug 2020 11:27

A-L-E-X wrote:
Source of the post On DPR someone named "Jack" captured a picture of the kind of color I saw, so maybe these multicolored meteors aren't so rare? 

No, not rare at all. The color change shown in his image looks exactly like the color change captured in one of my shots of another Perseid.  The green at the start of the trail has nothing to do with the composition of the meteor itself, and is instead due to the excitation of atmospheric atomic oxygen. Above about 90km, the pressure is low enough for a "forbidden transition" in oxygen which makes the green color, and it's exactly the same emission as the green aurora. This transition also has a couple seconds lifetime, so it often remains visible for a short while after the meteor has passed. The other colors appearing below that are a mix of both the meteor and the surrounding air being ionized.  (More details in my forum post here.)

Oh so if I want to narrow down the altitude range of what I saw, it would probably be somewhere between 20-35 km?

Probably closer to triple that. If the start of the trail is green and especially with a bit of green afterglow, that's a good indication of altitude since it only happens above about 90km.

I wonder if parts of it landed hundreds of yards away and I heard that?  Or if the sound was too soon after the bright flash to be that, maybe I heard the sound of the air heating up (or the meteor breaking up into smaller fragments mid air)?


If it dropped stones, they would have landed 100s of kilometers away.  Any sound you heard was not directly from the meteor or surrounding air (too soon for such a great distance for sound to travel), but probably radiation from the meteor interacting with the ground around you (a photo-acoustic coupling effect).
 
User avatar
midtskogen
World Builder
World Builder
Posts: 1032
Joined: 11 Dec 2016
Location: Oslo, Norway
Contact:

Astrophotography

17 Aug 2020 11:58

A-L-E-X wrote:
Source of the post Oh so if I want to narrow down the altitude range of what I saw, it would probably be somewhere between 20-35 km?  It was green, then yellow, then orange, and then a bright red and then there was a bright flash and then it was gone (and a split second after that I heard the pebble hitting a hard surface noise.)

Most meteors don't even go as deep as 40 km altitude.  That greatly depends on speed, and entry mass.  The faster, the less probability that it will make it deeper (which also might sound somewhat counter intuitive).  A sudden bright flash and then it was gone indicates that it came in at a high speed and evaporated above 40 km.  If you see it fizzle out over a few seconds after one or more flashes or fragmentations, then it's more likely that it reached 30 km or lower.  But since it changed from green to orange and red, it sounds like you saw it very low in the horizon and fragments could be too faint to see through more than 500 km of atmosphere, so it could well be something that went deep.

Here's an example of a fireball turning red.  It fizzled out 24 km above the ocean about 600 km away.
NIL DIFFICILE VOLENTI
 
User avatar
JackDole
Star Engineer
Star Engineer
Posts: 1845
Joined: 02 Nov 2016
Location: Terra

Science and Astronomy Questions

17 Aug 2020 20:45

Watsisname, it seems to work so far.
https://imgur.com/IoCcmmO.gifv
But what does this part sentence mean: for the spin parameter of 0.5
JackDole's Universe 0.990: http://forum.spaceengine.org/viewtopic.php?f=3&t=546
JackDole's Archive: http://forum.spaceengine.org/viewtopic.php?f=3&t=419
JackDole: Mega structures ... http://old.spaceengine.org/forum/17-3252-1 (Old forum)
 
User avatar
Watsisname
Science Officer
Science Officer
Posts: 1963
Joined: 06 Sep 2016
Location: Bellingham, WA

Science and Astronomy Questions

17 Aug 2020 23:43

JackDole, okay, looking at your animation for the star S4714, it looks like it completes 360 degrees of apsidal precession in about 33 orbits, whereas according to the table it should be 206.5 orbits. So it's too fast by a factor that looks exactly like 2pi, which makes me think that the meaning of "years" in SE was actually years to complete one 360° revolution worth of precession, rather than pi radians of precession (since there are 2pi radians in a circle). Fixing it is simple, all you need to do is multiply what you currently have by 6.283. I think it will be likewise for the nodal precession rate.

Aside from that adjustment, I think it is looking good! It is very cool to see these effects shown so vividly in the SE universe. :)


JackDole wrote:
Source of the post But what does this part sentence mean: for the spin parameter of 0.5

That means the spin of black hole (often written with a letter 'a' in the literature), and in units where no spin at all would be a=0, and a black hole spinning as rapidly as possible is a=1.  Since we don't yet know very well how fast SgrA* is spinning, this paper assumed an intermediate value of a=0.5.

A black hole's spin acts to literally drag the surrounding space around with it like a whirlpool (also called frame dragging), and this causes an additional precession on orbits and gyroscopes nearby (called Lense-Thirring precession). It's a very interesting effect that exists around all spinning masses (but is strongest near spinning black holes), and something that was predicted by Einstein's equations of general relativity, but only experimentally measured fairly recently with the Gravity Probe B experiment around Earth.
 
User avatar
JackDole
Star Engineer
Star Engineer
Posts: 1845
Joined: 02 Nov 2016
Location: Terra

Science and Astronomy Questions

18 Aug 2020 00:15

Watsisname wrote:
Source of the post whereas according to the table it should be 206.5 orbits.

How do you calculate it should be 206.5 orbits?
JackDole's Universe 0.990: http://forum.spaceengine.org/viewtopic.php?f=3&t=546
JackDole's Archive: http://forum.spaceengine.org/viewtopic.php?f=3&t=419
JackDole: Mega structures ... http://old.spaceengine.org/forum/17-3252-1 (Old forum)
 
User avatar
Watsisname
Science Officer
Science Officer
Posts: 1963
Joined: 06 Sep 2016
Location: Bellingham, WA

Science and Astronomy Questions

18 Aug 2020 00:40

JackDole wrote:
Source of the post How do you calculate it should be 206.5 orbits?

For δϕ=104.6 arcminutes = 1.743 degrees, that's 360/1.743 = 206.5 orbits for the apsides to precess by 360 degrees.

Added: such a precession rate is astonishing. For comparison, the general relativistic perihelion precession of Mercury's orbit is about 43 arcseconds per century, or about 12.5 million orbits to precess by a full 360 degrees. This star does it in only 207 orbits around SgrA*. Amazing. (It's worth pointing out that there are big error bars on that figure, but that's the best estimate.)
 
User avatar
JackDole
Star Engineer
Star Engineer
Posts: 1845
Joined: 02 Nov 2016
Location: Terra

Science and Astronomy Questions

18 Aug 2020 03:01

(https://imgur.com/QSbe248.gifv)

Sorry, wrong link. This is the right one.
https://imgur.com/1ZCRVX9.gifv
JackDole's Universe 0.990: http://forum.spaceengine.org/viewtopic.php?f=3&t=546
JackDole's Archive: http://forum.spaceengine.org/viewtopic.php?f=3&t=419
JackDole: Mega structures ... http://old.spaceengine.org/forum/17-3252-1 (Old forum)
 
User avatar
Watsisname
Science Officer
Science Officer
Posts: 1963
Joined: 06 Sep 2016
Location: Bellingham, WA

Science and Astronomy Questions

18 Aug 2020 03:31

Nice!  I think you got it.
 
A-L-E-X
Star Engineer
Star Engineer
Posts: 2139
Joined: 06 Mar 2017

Astrophotography

20 Aug 2020 15:26

The green color actually reminded me of what I see from certain emission nebulae with my O-2 filter.  Ironically, there are no green stars (since stars that mainly emit green light also emit a balance of other colors and therefore appear white.)  Why is it called the "forbidden transition" Wat?    It doesn't seem to be all that forbidden :P

Based on what you've both said, it seems that it would be above 40 km at the end when it "flashed", maybe having started out at around 80 km when I first saw it.  Those pictures are spectacular.  In the DPR thread, a composite image was posted that combined several colorful meteors into one.  I wonder what kind of lens I would need to capture this kind of color?

https://www.dpreview.com/forums/post/64262934

The people in that thread said I needed something really fast, like a 24mm f/1.4 lens.  I wish I had known that before, since I dumped some money into three zoom lenses- 14-42 f/3.5-f/5.6   40-150 f/4-f/5.6  and 75-300 f/4.8-f/6.7  I'm used to focal ratios between f/5 and f/6 because my fastest scopes are in that range, I didn't know you actually need a lens that is faster than f/2 to do astrophotography!  I'd like a nice wide lens which will have the Milky Way in the background (like I saw with my eyes) and the colorful meteors in the foreground.....I guess 24mm-28mm should be wide enough for that?

Who is online

Users browsing this forum: No registered users and 1 guest