How to identify that light in the sky | Hacker News Reader

How to identify that light in the sky

apod.nasa.gov

156 pointshoyd48 comments

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 :-)

> collision with Venus

It’s a reasonable concern! …if you’ve installed a Silmaril on your ship.

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...

Interesting. Thanks for the reference.

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...

There was a big scrolling marquis sign at ground level near a road I used to drive on frequently. At a certain point the letters had that "constant bearing" property. If I wasn't paying too much attention I would just get the feeling that ~something~ was coming fast at me from the side and would hit me.

I would have to fight my instinct to swerve away and consciously reassure myself that it was just the sign that I saw.

If it makes her feel better, professional pilots make the same mistake!

https://www.news.com.au/breaking-news/air-canada-pilot-misto...

> 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.)

Isn't this how the early AIM-9s worked?

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.

It's also an innate (or at least universally acquired) mental heuristic. IIRC, there are experiments showing that if, say, a baseball player can't readily make use of a fixed background by which to gauge and maintain a constant bearing viz-a-viz the object to be caught when positioning themself, their success rate plummets.

Searching for "Outfielder Problem" should bring up some interesting literature.

Mariner here, I've been in a similar situation on the Great Lakes (US). Absolutely the first thing I thought of.

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

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.

If we’re indoors, it’s a paid actor.

That's less accurate advice than you might think.

There are more volunteer actors than professional. Odds are high that they're actually unpaid.

I’d think odds are the ones I’m seeing on TV or in a movie are paid. (Most of the actors are unpaid. Most of the sightings of actors are probably of paid actors.)

Touche!

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.

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.

Why would it be related to the time of night?

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.

Only visible around sunset and sunrise, due to proximity to the sun.

If you see a really bright "star" near the sunset for example, it's almost certainly Venus.

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.

In that case you can just ask E.T. for directions.

Glaring omission: battlefield illumination flares

My cabin borders a massive Marine base (29 Palms) and there's often what appear to be UFOs hovering in formation for minutes at a time over the nearby mountain range. It's the Marines doing night exercises w/flares, and they just linger in place for a surprising amount of time. They must have parachutes or something keeping them afloat on the heated air.

Another tell for a satellite is if it's moving along then somewhere mid-trajectory it dims from white to deep red to gone.

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...

“Any sudden impossible changes of course?”

Yes - Aliens

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.

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.

https://twitter.com/MissLily_fj/status/1460905054513217536

This is urgently missing "Oil refinery gas flare" which competes with the moon in brightness around here :)

Special case of mast light.

Doesn't explain this light that was seen in the sky in Fiji three days ago https://twitter.com/MissLily_fj/status/1460905054513217536

Going by the flow chart, that's a planet.

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.

I’m disappointed they didn’t include one for UFOs. I thought they might since they had other jokes in the flowchart.

Why would it be a joke? Anything uncertain in the sky is a UFO almost by definition.

My guidance counselor advised for prep on the SAT math: “D means ‘cannot be determined by anyone’ not just ‘I cannot determine it’”

> "Are your retinas burning?"

Who thought the people at Nasa could not be funny!

My favorite was "are any astronauts waving at you"

Somehow this seems like it ought to be an xkcd comic.

Planets do twinckle

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.

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.

? November is not the dead of winter, there can still be warm days in the 50s and 60s. And anyway sometimes it's nice to be on a balcony even in the cold.

I witnessed a meteor/fireball on my Chicago balcony around 2009 or 2010, I remember thinking it must have been some kind of aircraft breaking up over the city, I went to Twitter thinking I would find out what happened but it wasn't til the next day I heard it was a meteor that ended up over Wisconsin.

I think it was April 2010: https://www.chicagotribune.com/news/ct-xpm-2010-04-15-ct-met...

> 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.

That's a strange assumption. Average temps in November aren't low at all either at night or during the day.

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