[HN Gopher] How to Identify that Light in the Sky (flowchart)
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How to Identify that Light in the Sky (flowchart)
Author : hoyd
Score : 98 points
Date : 2021-11-18 10:41 UTC (1 days ago)
(HTM) web link (apod.nasa.gov)
(TXT) w3m dump (apod.nasa.gov)
| nickcw wrote:
| Ha! I love the "Masthead Light" option - that reminds me of a
| story.
|
| When you are sailing at night you take bearings of lights you see
| with a hand-bearing compass. This is a device you look through
| and it tells you the magnetic bearing of the object you have
| lined up in the cross hairs. If you see a light that you can't
| identify then you take bearings on it over the course of a few
| minutes, and you remind yourself of the sailing motto, "If the
| bearing does not change, a collision will occur".
|
| I was on a night sail in the Mediterranean with one of my younger
| cousins who came down below in a panic to report we were on a
| collision course as the bearing of the light she had spotted was
| not changing.
|
| I think she could have done with this flow chart, because it
| turned out to be Venus :-)
| jhgb wrote:
| > and you remind yourself of the sailing motto, "If the bearing
| does not change, a collision will occur".
|
| It's also the anti-aircraft-missile's proportional guidance
| motto. (Being from a landlocked country, it doesn't surprise me
| that I learned about it from anti-aircraft missiles first.)
| gue-ni wrote:
| Isn't this how the early AIM-9s worked?
| jhgb wrote:
| It's pretty much how most modern missiles work, as far as I
| can tell, and it's very natural to use it on missiles with
| passive guidance in particular (as opposed to for example
| missiles with control guidance, the oldest of which used
| beam riding). Maybe some super-advanced ones calculate
| optimal trajectories of some sort but that requires more
| storage, more computing power, and perhaps even a way of
| estimating distance, whereas proportional guidance only
| requires angles.
| thewakalix wrote:
| > collision with Venus
|
| It's a reasonable concern! ...if you've installed a Silmaril on
| your ship.
| Galxeagle wrote:
| If it makes her feel better, professional pilots make the same
| mistake!
|
| https://www.news.com.au/breaking-news/air-canada-pilot-misto...
| _Microft wrote:
| If someone wants to know more about why such a situation would
| eventually result in a collision, look for the term "Constant
| bearing, decreasing range", e.g. in Wikipedia:
|
| https://en.wikipedia.org/wiki/Constant_bearing,_decreasing_r...
| jedimastert wrote:
| It did make me stop and think for a second. Like it totally
| makes sense, but I don't think I would have come up with that
| rule on my own for whatever reason. Of course, I don't do
| much in the way of sailing...
| henvic wrote:
| Interesting. Thanks for the reference.
| narag wrote:
| Star-like (4th to 5th mag) point, not blinking, moving across the
| night sky in about five minutes, consistent _sinusoidal_ (full
| moon wide) trajectory... this wasn 't too helpful, really.
| [deleted]
| astockwell wrote:
| As we all know, a decision tree without room for "Unknown
| Behavior" or error/failure modes (a.k.a. UFOs) is bound to result
| in a 2am page for a production outage very soon.
| teeray wrote:
| "Any sudden impossible changes of course?"
|
| Yes - Aliens
| JJMcJ wrote:
| Or not - old aircraft spotter joke "It approached me at great
| speed till it disappeared over the horizon".
|
| Really hard to tell when direction a plane is really headed in
| sometimes. So it can look like it made a 90 degree turn when it
| really didn't.
| genewitch wrote:
| I had a drone get out of video range once, and I couldn't
| tell which way it was moving. I would rotate, then strafe
| left. I never was able to rotate it enough to clearly see any
| left or right movement relative to me, so eventually it auto-
| returned and crashed with 0% battery about 50' from where I
| launched it.
|
| I should note it was either wind or microwaves that
| originallyl made it go out of video range, this was me trying
| to get an idea of flooding and hurricane damage the afternoon
| after hurricane Laura hit us.
| rossdavidh wrote:
| Somehow this seems like it ought to be an xkcd comic.
| jcims wrote:
| Another tell for a satellite is if it's moving along then
| somewhere mid-trajectory it dims from white to deep red to gone.
| dmurray wrote:
| My rule of thumb is, when someone asks "what's that star?" it's
| Venus. If it's later in the night, it's Jupiter.
| SamBam wrote:
| Or Mars, but what's nice is that you generally only have to
| look up what that "other planet" is once every few months or
| so, and you'll know it for a good long while. Right now it's
| Jupiter.
|
| Venus is actually surprisingly far from the sun right now,
| although still clearly the evening star.
| nanidin wrote:
| I whip out my phone, pull up Sky Guide, then point it at the
| star in question. Around here depending on the time of the year
| it's typically Jupiter, Mars, Venus, or Sirius.
| Razengan wrote:
| If we're indoors, it's a paid actor.
| recursive wrote:
| Why would it be related to the time of night?
| Uehreka wrote:
| Venus's orbit is between us and the Sun, so if it's going to
| be visible at all, it won't be at a time when your part of
| the Earth is facing totally away from the Sun. Venus would be
| visible a lot during the day if the Sun were less bright.
| [deleted]
| soamv wrote:
| Speaking of lights in the sky, I recently fell into a wikipedia
| rabbit hole and learned about the Gegenschein[0]. This is the
| backscatter reflection of sunlight from interplanetary dust. You
| need an extraordinarily dark sky to be able to see it.
|
| [0] https://en.wikipedia.org/wiki/Gegenschein
| csomar wrote:
| > "Are your retinas burning?"
|
| Who thought the people at Nasa could not be funny!
| KiranRao0 wrote:
| My favorite was "are any astronauts waving at you"
| oxymoran wrote:
| This doesn't help me identify the bright red orb that I saw weave
| in and out of buildings at breakneck speed through the Chicago
| skyline at 3am. It was also seen by my friend as we were out on
| the balcony looking at the city. And no, it was not an emergency
| vehicle, it went from one side of the city to the other in a few
| seconds and also changed altitude drastically multiple times as
| it made its way around building. The light was also solid, like
| it was emoting it's one light, not a reflection and it was very
| bright. It looked like a futuristic rollercoaster ride. This was
| over a decade ago, around the time of the famous O'hare ufo
| sighting.
| OldHand2018 wrote:
| Wikipedia says that happened in November 2006.
|
| Going out on a limb here, but I am betting that you and your
| friend weren't hanging out on the balcony at 3AM in winter in
| Chicago. Can we assume it was the following spring or summer?
|
| Because that's exactly when Christopher Nolan spent almost 4
| months filming the Dark Knight in downtown Chicago. I was
| working downtown at the time. A large part of the loop was the
| set. During the day all the props and equipment were stored on
| the sidewalks and street parking areas. Late at night they set
| it all up, did their filming, and then put it all away again.
| And yeah, they used black helicopters zooming around all over
| the place as camera platforms. Downtown isn't _that_ big, a
| helicopter can easily cross it in a matter of seconds.
|
| That's what you saw.
| kqbx wrote:
| The blog where the chart was originally posted has a slightly
| bigger version of the picture:
| https://www.leagueoflostcauses.com/blog/2013/08/astronomy-10...
| kamel3d wrote:
| Planets do twinckle
| xg15 wrote:
| This is urgently missing "Oil refinery gas flare" which competes
| with the moon in brightness around here :)
| irrational wrote:
| I'm disappointed they didn't include one for UFOs. I thought they
| might since they had other jokes in the flowchart.
| recursive wrote:
| Why would it be a joke? Anything uncertain in the sky is a UFO
| almost by definition.
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(page generated 2021-11-19 23:00 UTC)