APOD: How to Identify that Light in the Sky (2014 Jun 09)

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APOD: How to Identify that Light in the Sky (2014 Jun 09)

Postby APOD Robot » Mon Jun 09, 2014 4:10 am

Image How to Identify that Light in the Sky

Explanation: What is that light in the sky? Perhaps one of humanity's more common questions, an answer may result from a few quick observations. For example -- is it moving or blinking? If so, and if you live near a city, the answer is typically an airplane, since planes are so numerous and so few stars and satellites are bright enough to be seen over the din of artificial city lights. If not, and if you live far from a city, that bright light is likely a planet such as Venus or Mars -- the former of which is constrained to appear near the horizon just before dawn or after dusk. Sometimes the low apparent motion of a distant airplane near the horizon makes it hard to tell from a bright planet, but even this can usually be discerned by the plane's motion over a few minutes. Still unsure? The above chart gives a sometimes-humorous but mostly-accurate assessment. Dedicated sky enthusiasts will likely note -- and are encouraged to provide -- polite corrections.

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Re: APOD: How to Identify that Light in the Sky (2014 Jun 09

Postby Marc K Taylor » Mon Jun 09, 2014 4:48 am

I am sending this to the students in the class I just finished teaching. Maybe a wallet-sized card.

BUT... Planets do indeed twinkle, when they are low in the sky -- so strongly that it can look like they have flashing lights on them -- thus the hoary old "I saw a UFO!" "No, it was just Venus" because many times it was. What would you think, if you saw a brilliant light, low in the sky, seemingly "hovering" just the other side of those trees over yonder, with what seem to be brilliant, randomly strobing lights playing all over it? Little green men, of course!
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Re: APOD: How to Identify that Light in the Sky (2014 Jun 09

Postby Nitpicker » Mon Jun 09, 2014 4:49 am

The League of Lost Causes looks like a fun blog.

My understanding is that any slow moving, unresolved point source of light viewed through the atmosphere -- which includes all seven of the other planets in the Solar System, when viewed with unaided eyes (not that you can see them all unaided) -- may appear to twinkle or scintillate.

I was taught as a child that planets don't twinkle. It seems to be a common belief, almost a superstition. Since taking up astronomy as a hobby, I see twinkling planets (and stars) all the time. I prefer it when they don't twinkle.
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Re: APOD: How to Identify that Light in the Sky (2014 Jun 09

Postby geckzilla » Mon Jun 09, 2014 4:56 am

Haha, yeah, I think they appear to twinkle slightly less but they do still twinkle. Be nice to someone if they call a planet a star by mistake. It's not really that obvious.
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Re: APOD: How to Identify that Light in the Sky (2014 Jun 09

Postby Nitpicker » Mon Jun 09, 2014 5:16 am

geckzilla wrote:Haha, yeah, I think they appear to twinkle slightly less but they do still twinkle. Be nice to someone if they call a planet a star by mistake. It's not really that obvious.


Jupiter, Sirius and Canopus form an evenly spaced, almost horizontal straight line in my western sky of an evening at the moment. If I don't quite have my bearings and can't see all three together, it is easy to get 'em wrong.
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Re: APOD: How to Identify that Light in the Sky (2014 Jun 09

Postby Bjork » Mon Jun 09, 2014 5:32 am

scientists must stop asking silly questions like are we alone in the universe
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Re: APOD: How to Identify that Light in the Sky (2014 Jun 09

Postby geckzilla » Mon Jun 09, 2014 5:47 am

Bjork wrote:scientists must stop asking silly questions like are we alone in the universe

I hope we never stop until it's answered.
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Re: APOD: How to Identify that Light in the Sky (2014 Jun 09

Postby staffastro » Mon Jun 09, 2014 6:43 am

I would not classify the sun and moon as 'really big', but an aurora or a great comet might be...
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Re: APOD: How to Identify that Light in the Sky (2014 Jun 09

Postby hoohaw » Mon Jun 09, 2014 9:01 am

It's a bird! It's a plane! It's ... Superman!
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Re: APOD: How to Identify that Light in the Sky (2014 Jun 09

Postby Javachip » Mon Jun 09, 2014 9:12 am

A few years ago, I was visiting Palm Springs, California. Late at night, I noticed a stationary bright point of light to the west about 15 degrees above the horizon. It was as bright as Venus, but Venus is never visible in the middle of the night. It did not move or change in any way during several minutes of observing. Was it a supernova? Finally I realized that I was viewing a light bulb on a nearby mountain.
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Re: APOD: How to Identify that Light in the Sky (2014 Jun 09

Postby Boomer12k » Mon Jun 09, 2014 9:44 am

They forgot.....Did it land on the road in front of you as you came around a corner, and when you came to, you forgot the last 3 hours of your life....except for Regression Therapy, that shows you were abducted....?

It happened to a cop that was chasing a UFO....others were chasing it also...a LOT of others....

Also....did it just go straight up, and not across the sky?....and did it disappear going straight up, and not across the sky?....Like what I saw when I was a child....I tell you it went up, and up, and up.....

Also....did it shoot down from the sky....then cut at a 45 degree angle....shoot off in the distance too rapid to anything with an Air Breathing Engine????? As one of my friends saw.....

Yup....The little Flow Chart is a bit limited in scope....

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Re: APOD: How to Identify that Light in the Sky (2014 Jun 09

Postby inertnet » Mon Jun 09, 2014 9:54 am

I would have added this question somewhere in there: "Did the railroad crossing lights go berserk?"

Also, it is said that some galaxies are visible to the unaided eye from the southern hemisphere. I never had the opportunity to see for myself yet.
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Re: APOD: How to Identify that Light in the Sky (2014 Jun 09

Postby Nitpicker » Mon Jun 09, 2014 10:42 am

inertnet wrote:Also, it is said that some galaxies are visible to the unaided eye from the southern hemisphere. I never had the opportunity to see for myself yet.


Only the LMC and SMC, I think. To my unaided eyes, through mild-to-moderate light pollution, they look like bits of Milky Way fluff that got a bit lost.
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Re: APOD: How to Identify that Light in the Sky (2014 Jun 09

Postby BDanielMayfield » Mon Jun 09, 2014 12:02 pm

geckzilla wrote:
Bjork wrote:scientists must stop asking silly questions like are we alone in the universe

I hope we never stop until it's answered.

It's not a silly question, no matter where one bias lays as to our origins. And when it is answered, (positively, I expect) it should have a profound effect on our thinking.

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Re: APOD: How to Identify that Light in the Sky (2014 Jun 09

Postby CURRAHEE CHRIS » Mon Jun 09, 2014 12:30 pm

"Are your retinas burning?" for some reason that question cracked me up. :shock:

That was comical and very enjoyable. Great way to start out a monday.
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Re: APOD: How to Identify that Light in the Sky (2014 Jun 09

Postby CharliePatriot » Mon Jun 09, 2014 12:33 pm

The other evening here in southern Ohio, I noticed a satellite traveling west to east, when it went into shadow of earth it disappeared since the sunlight was no longer reflecting from it. Shortly after I saw another traveling in the same direction only slightly further north. What troubled me with this one is that it went all the way until going below the horizon, remaining at the same level of brightness..??? Any ideas.?
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Re: APOD: How to Identify that Light in the Sky (2014 Jun 09

Postby gjenkins » Mon Jun 09, 2014 1:06 pm

Perhaps another consideration should include the question: "is it moving in a straight line"
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Re: APOD: How to Identify that Light in the Sky (2014 Jun 09

Postby neufer » Mon Jun 09, 2014 1:16 pm

CharliePatriot wrote:
The other evening here in southern Ohio, I noticed a satellite traveling west to east, when it went into shadow of earth it disappeared since the sunlight was no longer reflecting from it. Shortly after I saw another traveling in the same direction only slightly further north. What troubled me with this one is that it went all the way until going below the horizon, remaining at the same level of brightness..??? Any ideas.?

Any satellite above ~800 km will remain in permanent sunshine this time of year so long as it stays north of ~39º latitude.

(The higher the satellite the less likely it's apparent brightness will change much from zenith to the horizon.)
Last edited by neufer on Mon Jun 09, 2014 2:00 pm, edited 1 time in total.
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Re: APOD: How to Identify that Light in the Sky (2014 Jun 09

Postby Zuben L. Genubi » Mon Jun 09, 2014 1:26 pm

So... lights in the sky. The morning of the Camelopardidn''t meteor storm, I was out in the country between the hours of 0300 and 0400 EST and did see, among other things, seven fairly slowly-moving, non-blinking objects. Movement was uniform in speed and direction. Most passed within several degrees of directly overhead. When I checked websites to help me identify satellites that might have passed over at that time, there might have been one listed - but not seven. All moved at about the same speed. There was no sound (such as the distant roar of jet engines that usually follows high-flying aircraft, except that of a mooing cow toward 0400 - and I don't believe that came from any of these on objects. Any ideas???
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Re: APOD: How to Identify that Light in the Sky (2014 Jun 09

Postby gosforsyke » Mon Jun 09, 2014 1:32 pm

This chart needs to be printed, laminated, and prominently posted on the Conn of every submarine whenever a newly qualified Officer of the Deck is preparing to go to periscope depth. It is not unheard of for an inexperienced OOD to shout "Emergency Deep!" as the periscope breaks the surface at night facing the Moon, Venus, or Jupiter! That announcement, especially if accompanied by the sounding of the Collision Alarm, has a way of breaking a sound sleep for off-watch personnel! Been there, done that!
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Re: APOD: How to Identify that Light in the Sky (2014 Jun 09

Postby neufer » Mon Jun 09, 2014 1:53 pm

CURRAHEE CHRIS wrote:
"Are your retinas [sic] burning?" for some reason that question cracked me up. :shock:

    retinae
http://en.wikipedia.org/wiki/Pecten_oculi wrote:

<<The pecten or pecten oculi is a comb-like structure of blood vessels belonging to the choroid in the eye of all birds and some reptiles. In the vertebrate eye, blood vessels lie in front of the retina, partially obscuring the image. The pecten helps to solve this problem by greatly reducing the number of blood vessels in the retina and leading to the extremely sharp eyesight of birds such as hawks. It is a non-sensory, pigmented structure that projects into the vitreous body from the point where the optic nerve enters the eyeball. The pecten is believed to both nourish the retina and control the pH of the vitreous body. The pigmentation of the pecten is believed to protect the blood vessels against damage from ultraviolet light. Stray-light absorption by melanin granules of pecten oculi is also considered to give rise to small increments in temperature of pecten and eye; this may offer increased metabolic rate to optimize eye physiology in low temperatures at high-altitude flights. The structure varies across bird species and is conical in the kiwi, vaned in the ostrich and pleated in most other birds.>>
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Re: APOD: How to Identify that Light in the Sky (2014 Jun 09

Postby Psnarf » Mon Jun 09, 2014 2:23 pm

Weather balloons sent aloft during twilight will reflect the sun when they get high enough. When such objects are moving directly toward you, they appear stationary. However, rivers of air can criss-cross, causing the balloons to rapidly change direction. Then when they get to a jet stream, off they go. If away from the rising/setting sun, they'll eventually vanish. There is no correlation between lights in the sky, moving or not, and craft from beyond the solar system. To increase the conundrum, we now have piloted balloons and drones. The religious fervor of those of the space-monkey persuasion astounds me.
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Re: APOD: How to Identify that Light in the Sky (2014 Jun 09

Postby Terry Danks » Mon Jun 09, 2014 2:35 pm

Some thirty years ago I looked up from my telescope to be astonished by a very bright light moving with unbelievable speed across the sky.
Or so it seemed.
Instead of a bright, distant and fast moving object, it was actually a slow moving, nearby and faint . . . firefly!
True story.

I have also observed a small pilot balloon used by weather observers at night. The small light they carry suspended beneath them moves in a jerky fashion and looks very peculiar in a night sky against the stars.
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Re: APOD: How to Identify that Light in the Sky (2014 Jun 09

Postby Chris Peterson » Mon Jun 09, 2014 2:35 pm

Nitpicker wrote:I was taught as a child that planets don't twinkle. It seems to be a common belief, almost a superstition. Since taking up astronomy as a hobby, I see twinkling planets (and stars) all the time. I prefer it when they don't twinkle.

It's still a good rule of thumb. Even under terrible seeing conditions (like I have under the jetstream here in Colorado) it is rare for a planet above 20 or 30 degrees altitude to twinkle anywhere near as much as a star. It only takes a few inch wide ray path through the atmosphere to significantly reduce or eliminate scintillation (which is why stars rarely twinkle when seen through binoculars).

When I've got a group outside under the stars, I explain where the scintillation comes from, and show them (if the right objects are present) how different planets and stars always appear if you look at them critically.

(Check out Jupiter in the evening sky right now- a brilliant evening "star", which even very low looks nothing like any of the bright stars around it, such as Procyon or Capella. They may all be twinkling, but there's an obvious qualitative difference between the planet and the stars. Obvious if you make the effort to actually observe, that is. Most people don't- most people outside forums like this, anyway. BTW, Mercury is visible now, as well. It's not bright enough, or contrasty enough against the light sky, to normally show twinkling, even right on the horizon.)
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Re: APOD: How to Identify that Light in the Sky (2014 Jun 09

Postby Chris Peterson » Mon Jun 09, 2014 2:38 pm

Zuben L. Genubi wrote:So... lights in the sky. The morning of the Camelopardidn''t meteor storm, I was out in the country between the hours of 0300 and 0400 EST and did see, among other things, seven fairly slowly-moving, non-blinking objects. Movement was uniform in speed and direction. Most passed within several degrees of directly overhead. When I checked websites to help me identify satellites that might have passed over at that time, there might have been one listed - but not seven. All moved at about the same speed. There was no sound (such as the distant roar of jet engines that usually follows high-flying aircraft, except that of a mooing cow toward 0400 - and I don't believe that came from any of these on objects. Any ideas???

I'd assume satellites. Many more are visible than can easily be identified, both because many dimmer ones aren't tested for by identification tools, and because many are classified and don't have official elements listed (although nearly all have unofficial elements provided by amateur observers).
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