View Full Version : Astronomical Questions

3rd Sep 2016, 12:01
Knowing that there are a few on JB who are very knowledgeable about matters astronomical I have some Q's that need A's. Last week I had the good fortune to go hiking in the Swiss Alps and slept out under the stars for two nights. The night sky was so mesmerising that more watching and less sleeping was the end result.

A) There were many shooting stars, mostly 'thin' in form, perhaps part of the Perseid Meteor Shower , however several were much larger and 'wide' in form. One of these was quite spectacular with a strong green/blue hue as it came through the upper atmosphere. Would this have been the plasma caused by the heating of iron within the meteor perhaps ?

B) Loads of satellites traversing the heavens, from all directions, some flying in an almost parallel orbit. Obviously due to different perspectives and distances from earth the speed of the sortiment varied greatly (visually), but some of them were really travelling leisurely, whilst others were in a hurry. Why would this be in general terms ?

C) During the course of the nights, I observed many flashes, mostly small and concentrated. Most were directly above (and looked like when a pebble hits the surface of a still pond), others were 45deg away from my viewpoint. Could these have been sprites ? There was no 'weather' anywhere for 200miles btw.

For a city resident used to the muted night sky, the magnificence of an unpolluted night sky was a wonder to behold and it reminded me why ancient man had a detailed knowledge of the stars and their orbit in the heavens.

3rd Sep 2016, 12:13
A) You're probably right, The green colour would almost certainly been down to the chemical composition of the meteor, you sometimes get red produced by air molecules..

B) Lower satellites travel faster, higher ones slower. FWIW most satellites travel appear to travel westish to eastish ( because by launching them in that direction the Earth's spin gives a head start on the way to the required required orbital velocity)

C) No idea, remisent of the thread we had a while ago about somebody in Lincolnshire seeing something that looked like a firework overhead on a clear night . TBH I've spent plenty of time out of doors at night over the decades ( all completely innocent, honest) and never seen anything similar - other than iridum flares, which are not so much flashes as a rapid brightning and then dimming of a satellite, usually over a period of several seconds.
I doubt it would be sprites in the abscence of CBs ( and sprites are very hard to see visually anyway, they are usually caught on "high speed" imagery.

the magnificence of an unpolluted night sky was a wonder to behold

Yep, it's one of the main reasons we chose to live out in the sticks.

Mr Optimistic
3rd Sep 2016, 13:32
Suspect colour was ionised oxygen and nitrogen, ie is the air not the composition of the object. Bow shock wave gives the air a bit of a shoeing.

uffington sb
3rd Sep 2016, 14:06
Check out Iridium flares on this website for para C.

Heavens-Above (http://www.heavens-above.com/?Session=kebgfecghbacekcghehbjidb)

3rd Sep 2016, 15:15
The colors of this shooting star may also indicate the minerals that make up the space rock. Different elements emit different-colored light when they burn. Iron, one of the most common elements found in meteors, glows yellow. Silicates, which contain a form of the element silicon, glow red. A green glow, clearly visible in the trail of this shooting star, indicates the presence of burning copper.
Shooting Star - National Geographic Society (http://nationalgeographic.org/media/shooting-star-spec/)

So probably a copper meteorite.

A satellite requires a speed of 17,450 miles per hour in order to maintain a low Earth orbit. Satellites in higher orbits travel more slowly; for example, a geostationary satellite only orbits at 6,858 miles per hour.

A north-south orbit often indicates a spy satellite!
Is there any way to see satellites that are in orbit? | HowStuffWorks (http://science.howstuffworks.com/question384.htm)

Satellite flare, also known as satellite glint, is the phenomenon caused by the reflective surfaces on satellites (https://en.wikipedia.org/wiki/Artificial_satellite) (such as antennas (https://en.wikipedia.org/wiki/Antenna_%28radio%29), SAR (https://en.wikipedia.org/wiki/Synthetic_aperture_radar) or solar panels (https://en.wikipedia.org/wiki/Photovoltaic_module)) reflecting sunlight directly onto the Earth below and appearing as a brief, bright "flare".
The Iridium constellation (https://en.wikipedia.org/wiki/Iridium_satellite_constellation) with 66 active telecommunication satellites in low Earth orbit are known to cause the brightest flares of all orbiting satellites.


3rd Sep 2016, 19:44
Thanks for the replies chaps. The satellites were mostly 'West-ish to East-ish', although there were also N-S and S-N and SE-NW etc. The visual size was always very similar despite differing heights above the earth. Perhaps this is explained by the increased flare of the sun the higher the orbit and the less the lower they were, assuming that they were mostly the same size. I didn't see any Iridium flares, but did note the odd one that must have been rotating/tumbling as it flared several times during it's trip across the sky.

So probably a copper meteorite.

It must have been a reasonable lump because both the dispersal and flare were notably large, albeit a few seconds in time. All the sightings were from approximately 2500metres up in clear air, so the visibility, although not world class, was pretty good. A visit to the Mauna Kea observatories some years back gave me a hard beginning to beat :-)

3rd Sep 2016, 21:45
The colours are likely due to refraction from looking through the bottom of your beer glass

Sue VÍtements
4th Sep 2016, 00:42
No, that's Breast Size :=

What's the name of that strange egg shaped orbit? Something Russian that gives a satellite a larger useful transit time. I can only think of Markov, but that's not it :(

4th Sep 2016, 04:07
Knowing that there are a few on JB who are very knowledgeable about matters astronomical

Perhaps he is thinking of my Ex-Missus Support demands!:uhoh:

4th Sep 2016, 04:11
I can only think of MarkovOrbits, but not of the satellite kind. Perhaps you are thinking of Milankovitch cycle?


Types of orbits mentioned here. Molniya orbit perhaps?


Mr Optimistic
4th Sep 2016, 09:27
What do you mean by ' like when a pebble hits the surface is of a still pond'?
I think colour much more likely to be the atmosphere than composition of object, check out aurora colours.
For a satellite the centrifugal force must balance gravity so speed squared divided by orbit radius equals local gravity which itself varies by reciprocal of r squared. So all in all I reckon orbital speed varies as one over square root of r. Larger orbits are slower speed and the angular rate you perceive also varies as reciprocal of r so low orbits are, and seem, much quicker. Need low orbits for earth observation and the like.

4th Sep 2016, 09:56
I think colour much more likely to be the atmosphere than composition of object

If you mean the colour of meteor trails I'm afraid you might want to have a rethink..

The study of meteor spectra has been going on for decades plus ( I did some very basic observations on it as part of a Univeristy project) , and there's absolutely no doubt that the majority of colours seen are down to the chemical composition of the meteor itself. You may get a minor contribution to the visible spectrum from atmospheric gases but most of the atmospheric gases contribution output falls into the Infra Red part of the spectrum.

There's a very very basic run down on the subject here.

Society for Popular Astronomy - MeteorSectionMeteor Spectra overview (http://popastro.com/meteor/observingmeteors/spectra/index.php)

In the case of Aurora, different process, different energies involved but yes, those colours are down to atmospheric gas.

4th Sep 2016, 09:57
What do you mean by ' like when a pebble hits the surface is of a still pond'?

So….Oneself lying on one's back staring up at the almost unpolluted night sky. Field of view perhaps 160-180degs. Mostly staring up at 0deg and peripheral vision allowing observation to both sides. The 'flashes' as they were, were concentrated in the 270deg to 0deg quadrant and 0deg to 90deg quadrant, though mostly closer to the 0deg point, above one's viewing point. In the darkness it was possible to see that the flash emanated in a point, expanded in sort of concentric circles and then dissipated all in perhaps 2-3secs. These occurrences were many during the night, but irregular/random and didn't spread visually very far. Perhaps I was witnessing meteorites hitting the atmosphere straight on ?

4th Sep 2016, 10:13
In the darkness it was possible to see that the flash emanated in a point, expanded in sort of concentric circles and then dissipated all in perhaps 2-3secs. These occurrences were many during the night, but irregular/random and didn't spread visually very far. Perhaps I was witnessing meteorites hitting the atmosphere straight on ?

Looks like the previous thread on a similar observation has gone.

From personal experience observing from dark sky sites I reckon you'd be lucky to see more than handful of meteors in a life time that entered "head on" and left absolutely no trail.

There are plenty of amateur astronomers these days who have very capable automated all sky cameras working throughout the hours of darkness ( for meteor research) and I've never heard of anything imaged that fits in with your description, and I have to admit I cannot think of anything astronomical that can cause what you describe, other than (and I'm going out on a limb here ) perhaps it was a manifestation of normal trails picked up in your peripheral vision.

Mr Optimistic
4th Sep 2016, 21:44
What color are meteors? (Beginner) - Curious About Astronomy? Ask an Astronomer (http://curious.astro.cornell.edu/about-us/73-our-solar-system/comets-meteors-and-asteroids/meteors/304-what-color-are-meteors-beginner)

As for the sparkles, may be check with your optician next time you have a check: maybe it's a known effect.

4th Sep 2016, 22:02
TBH the Cornell article really is broad brush - yes the atmospheric gases can produce some colouration but rarely (if ever) the short wavelength colours that the OP describes (i.e blue/green) those will be down to the chemical composition of the meteor. For example from the SPA paper I provided a link to earlier.

"One example, for a Perseid whose spectrum was imaged.... There is a bright green emission line from magnesium, along with a yellow emission line from sodium. Many meteors also show an emission line in the red from calcium, but this is not clearly seen here. The lines in the infrared are mostly related to the atmospheric gases with which the meteoric particle collided - the presence of these atmospheric lines in all spectra helps calibrate the wavelengths in the remainder of the spectrum."

For the hard of sleeping there's a more geeky paper more here, which starts with a brief history of this fascinating field of study.....:8


Apologies if I seem overly enthusiastic about this but I spent a part of my final under grad year working on this very subject, way back in the days of films, wet glass plates and dark rooms. It wasn't the most exciting project in the world and made me realise a career as an astronomer was not for me. The only good thing was the working hours it kept me out of the bar in the evenings for a few months and probably saved a few brain cells...or perhaps not....

Loose rivets
4th Sep 2016, 22:44
My pal saying he could see the lumps of rock and indeed gave a complex description of the tail seems very far fetched, except he's not into telling porkies and has some of the most exotic kit for night vision you could imagine.

As I've mentioned, he lives in just about the best place in Essex to have seen the 'storm' and around at 02:00 for the best show.

Frankly, I'm puzzled.

iridum flares You could set your clocks by them in the Texas night sky. Oh, and I learned what they were on this very forum.

Mr Optimistic
5th Sep 2016, 20:18
No problem, curious myself. The eye isn't a spectrometer however, so sensitivity to green will distort perception.

5th Sep 2016, 20:41
The highly elliptical Rusian satellites use the: https://en.wikipedia.org/wiki/Molniya_orbit

Over a point at high lattitude (55N) this would remain almost stationary for 8 hours out of the 12 hour period, but the altitude would be so high (40,000 km) that it would be invisible to the naked eye.

6th Sep 2016, 10:25
Good to see that 'townies' like SpringHeeledJack are getting to learn some of the delights of the 'countryside'. Pity, in a way, that he focused so much of his attention on the 'man-made' aspects of space!! Look beyond that at the beautiful universe out there. You are looking into the past: what you are looking at happened a long time ago, the same as when you hear a thunderclap you are listening to something that happened a while before. A lot of what you see has happened a long, long, long time in the past.

SpringHeeledJack, I hope that you enjoy a lot more of your recent discovery. And help to work against that scourge of the 'advanced' world: light pollution. Get a telescope, even a rather basic one. I read somewhere once that the first reaction on seeing Saturn's rings is always 'wow'; the first time that I was shown Saturn's rings through a telescope my reaction was 'WOW'!!

6th Sep 2016, 11:08
I remember seeing Jupiter's moons for the first time as a kid. I was amazed that I could actually see them moving!

6th Sep 2016, 11:35
Where I live I see the best star field by looking in a North Easterly direction that is away from the huge light/Sky reflection of the East Lancs industrial towns leading towards Manchester, by comparison that NE direction is a Black as needed to see much details of the star systems that the N Hemisphere has to offer..Last night in particular was very dark and surprisingly at around 2300 I saw many satellites going from W to E but also 3 going from S to N they were much faster than the ones going W/E.
Very relaxing with a nice glass of Amber warming fluid.. ;) It may be too warm to see anything tonight with the high cloud cover currently hardly moving.

Mr Optimistic
6th Sep 2016, 20:54
Just been to the Isle of Man on holiday. They pride themselves on the number of ' dark sky' sites. Fair enough. At Sulby reservoir they even had a sign to explain the opportunity to show what could be seen in winter and summer. So a nice picture of the constellations visible at 8pm in winter together with the equivalent at 8pm in summer. Good luck with the summer viewing I thought. Odd what government officials don't know.

6th Sep 2016, 22:48
I occasionally drive across Carter Bar (A68) at night.
In winter, especially when there is a clear sky, the abundance of celestial objects that can be observed is mind-blowing.

There is a large area of Northumberland that is designated as 'dark skies' as there is no conurbation for several miles.

7th Sep 2016, 00:12
Good to see that 'townies' like SpringHeeledJack are getting to learn some of the delights of the 'countryside'.
The countryside - AND the night view from the cockpit with the lights down :D