APOD: Lunar Eclipse Perspectives (2020 Feb 05)

Comments and questions about the APOD on the main view screen.
User avatar
APOD Robot
Otto Posterman
Posts: 4077
Joined: Fri Dec 04, 2009 3:27 am

APOD: Lunar Eclipse Perspectives (2020 Feb 05)

Post by APOD Robot » Wed Feb 05, 2020 5:05 am

Image Lunar Eclipse Perspectives

Explanation: Do we all see the same Moon? Yes, but we all see it differently. One difference is the apparent location of the Moon against background stars -- an effect known as parallax. We humans use the parallax between our eyes to judge depth. To see lunar parallax, though, we need eyes placed at a much greater separations -- hundreds to thousands of kilometers apart. Another difference is that observers around the Earth all see a slightly different face of our spherical Moon -- an effect known as libration. The featured image is a composite of many views across the Earth, as submitted to APOD, of the total lunar eclipse of 2019 January 21. These images are projected against the same background stars to illustrate both effects. The accurate superposition of these images was made possible by a serendipitous meteorite impact on the Moon during the lunar eclipse, labeled here L1-21J -- guaranteeing that these submitted images were all taken within a split second.

<< Previous APOD This Day in APOD Next APOD >>

User avatar
MarkBour
Subtle Signal
Posts: 1102
Joined: Mon Aug 26, 2013 2:44 pm
Location: Illinois, USA

Re: APOD: Lunar Eclipse Perspectives (2020 Feb 05)

Post by MarkBour » Wed Feb 05, 2020 6:34 am

I'm having trouble with today's image and the caption's explanation.

All of these images captured the meteor strike. There's a bit of philosophy to get through before one would conclude that they were all taken "simultaneously", but I can get there, near enough.

Now I think the composer(s) of today's APOD used a single image of the background stars and used it to place the different photos of the Moon into a single image. So, if the "fixed stars" are fixed (they must have rotated and magnified the separate images until the stars all lined up among them) then one has the Moon seemingly at different positions against this background. So, I can get the notion of parallax. Seen from Cape Verde, for example, the Moon is offset against said background versus when it was viewed at the same moment from the Czech Republic, by more than a full lunar diameter.

But I'm not seeing libration exemplified in this image.

At the lower right, there are three labels: Germany, Austria, and the Czech Republic. Comparatively close observatories compared to the other locations. I guess all three show the Moon nearly on top of each other, so at first I thought that was just one image of the Moon. Do these 3 somehow show libration in action? I would certainly welcome a further explanation, if that is the case.
Mark Goldfain

User avatar
orin stepanek
Plutopian
Posts: 5766
Joined: Wed Jul 27, 2005 3:41 pm
Location: Nebraska

Re: APOD: Lunar Eclipse Perspectives (2020 Feb 05)

Post by orin stepanek » Wed Feb 05, 2020 12:21 pm

LunarParallaxB_PonEtal_960.jpg

Wow! 8-) Getting an impact of a meteor during an eclipse Quite impressive; for me anyway! :mrgreen: But I guess it was known before the event!
You do not have the required permissions to view the files attached to this post.
Orin

Smile today; tomorrow's another day!

User avatar
Case
Commander
Posts: 602
Joined: Sat Jun 09, 2007 10:08 pm
Location: (52°N, 06°E)

Re: APOD: Lunar Eclipse Perspectives (2020 Feb 05)

Post by Case » Wed Feb 05, 2020 12:48 pm

orin stepanek wrote:
Wed Feb 05, 2020 12:21 pm
But I guess it was known before the event!
It wasn’t.
Moon Struck - 25 January 2019 - APOD

bls0326
Ensign
Posts: 91
Joined: Tue Mar 26, 2013 10:18 pm

Re: APOD: Lunar Eclipse Perspectives (2020 Feb 05)

Post by bls0326 » Wed Feb 05, 2020 2:18 pm

I happened to take pictures of the 2019 lunar eclipse within a few minutes on either side of the meteor strike time. What I notice is that my view of the moon is rotated as compared to views published at the time showing the strike location. My picture is on the left (just a handheld point/shoot camera) of my attachment.

My location is 35d10mN, 101d54sW and I assume the telescope in Spain is located about 37d,16N, 6d55sW. Quite a difference in how we are viewing the moon at the same time and about the same latitude. Unless the published picture is rotated for some reason such as to show the meteorite stike coming down on the moon. I know my picture is how I was actually seeing the moon.
You do not have the required permissions to view the files attached to this post.

TheZuke!
Science Officer
Posts: 184
Joined: Fri Mar 22, 2019 2:19 pm

Re: APOD: Lunar Eclipse Perspectives (2020 Feb 05)

Post by TheZuke! » Wed Feb 05, 2020 2:20 pm

Okay,
What is the "BD" and other annotations on the APOD photo?
I'm confused.

User avatar
Chris Peterson
Abominable Snowman
Posts: 15326
Joined: Wed Jan 31, 2007 11:13 pm
Location: Guffey, Colorado, USA

Re: APOD: Lunar Eclipse Perspectives (2020 Feb 05)

Post by Chris Peterson » Wed Feb 05, 2020 2:33 pm

TheZuke! wrote:
Wed Feb 05, 2020 2:20 pm
Okay,
What is the "BD" and other annotations on the APOD photo?
I'm confused.
L1-21J is the lunar impact. All the others- BD, HD, TYC are stellar catalog designations, i.e. identified stars.
Chris

*****************************************
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

User avatar
orin stepanek
Plutopian
Posts: 5766
Joined: Wed Jul 27, 2005 3:41 pm
Location: Nebraska

Re: APOD: Lunar Eclipse Perspectives (2020 Feb 05)

Post by orin stepanek » Wed Feb 05, 2020 3:03 pm

Case wrote:
Wed Feb 05, 2020 12:48 pm
orin stepanek wrote:
Wed Feb 05, 2020 12:21 pm
But I guess it was known before the event!
It wasn’t.
Moon Struck - 25 January 2019 - APOD
Makes it even more impressive! 8-)
Orin

Smile today; tomorrow's another day!

User avatar
owlice
Guardian of the Codes
Posts: 8376
Joined: Wed Aug 04, 2004 4:18 pm
Location: Washington, DC

Re: APOD: Lunar Eclipse Perspectives (2020 Feb 05)

Post by owlice » Wed Feb 05, 2020 4:40 pm

Congratulations to Matipon!!
A closed mouth gathers no foot.

Deathfleer

Re: APOD: Lunar Eclipse Perspectives (2020 Feb 05)

Post by Deathfleer » Wed Feb 05, 2020 8:05 pm

Great ...SubhanAllah... superimposing eclipse images from different countries....very brilliant novel idea.

User avatar
neufer
Vacationer at Tralfamadore
Posts: 17525
Joined: Mon Jan 21, 2008 1:57 pm
Location: Alexandria, Virginia

Re: APOD: Lunar Eclipse Perspectives (2020 Feb 05)

Post by neufer » Wed Feb 05, 2020 10:24 pm


orin stepanek wrote:
Wed Feb 05, 2020 12:21 pm

Wow! 8-)

Getting an impact of a meteor during an eclipse

Quite impressive; for me anyway! :mrgreen:
https://www.etymonline.com/search?q=moon wrote:
moon (v.) c. 1600, "to expose to moonlight;" later "idle about, wander or gaze moodily" (1836), "move listlessly" (1848), probably on the notion also found in moonstruck.

The meaning "to flash the buttocks" is recorded by 1968, U.S. student slang, from moon (n.) "buttocks" (1756), "probably from the idea of pale circularity" [Ayto].
Art Neuendorffer

User avatar
orin stepanek
Plutopian
Posts: 5766
Joined: Wed Jul 27, 2005 3:41 pm
Location: Nebraska

Re: APOD: Lunar Eclipse Perspectives (2020 Feb 05)

Post by orin stepanek » Thu Feb 06, 2020 1:28 am

neufer wrote:
Wed Feb 05, 2020 10:24 pm

orin stepanek wrote:
Wed Feb 05, 2020 12:21 pm

Wow! 8-)

Getting an impact of a meteor during an eclipse

Quite impressive; for me anyway! :mrgreen:
https://www.etymonline.com/search?q=moon wrote:
moon (v.) c. 1600, "to expose to moonlight;" later "idle about, wander or gaze moodily" (1836), "move listlessly" (1848), probably on the notion also found in moonstruck.

The meaning "to flash the buttocks" is recorded by 1968, U.S. student slang, from moon (n.) "buttocks" (1756), "probably from the idea of pale circularity" [Ayto].
Have you ever been mooned? :mrgreen:
Orin

Smile today; tomorrow's another day!

User avatar
neufer
Vacationer at Tralfamadore
Posts: 17525
Joined: Mon Jan 21, 2008 1:57 pm
Location: Alexandria, Virginia

Re: APOD: Lunar Eclipse Perspectives (2020 Feb 05)

Post by neufer » Thu Feb 06, 2020 3:44 am

orin stepanek wrote:
Thu Feb 06, 2020 1:28 am

Have you ever been mooned? :mrgreen:
  • Not that I recall.
However, while I was "idling about, wandering & gazing moodily" at today's APOD
I felt obliged to imprint this thought on all those unfortunate enough to read my posts.
Art Neuendorffer

Jerry Harlow
Asternaut
Posts: 1
Joined: Thu Feb 06, 2020 4:04 am

Re: APOD: Lunar Eclipse Perspectives (2020 Feb 05)

Post by Jerry Harlow » Thu Feb 06, 2020 4:20 am

I am having a hard time wrapping my brain around the geometry of the parallax. I would like to see a plot of the sight lines to the moon and one of the fixed stars, maybe HD 67564, from the perspective of Polaris. THX.

User avatar
RJN
Baffled Boffin
Posts: 1574
Joined: Sat Jul 24, 2004 1:58 pm
Location: Michigan Tech

Re: APOD: Lunar Eclipse Perspectives (2020 Feb 05)

Post by RJN » Thu Feb 06, 2020 3:42 pm

Here is a news story about this image/APOD:
https://www.novinky.cz/veda-skoly/clane ... i-40312366

Pon
Ensign
Posts: 19
Joined: Thu Jan 26, 2012 10:36 am

Re: APOD: Lunar Eclipse Perspectives (2020 Feb 05)

Post by Pon » Thu Feb 06, 2020 4:12 pm

Hi, I'm the person who composed the image and the text. There seems to be a few questions regarding the post, allow me to try to explain some of them.

Simultaneity:

- All these images were taken with different exposure time, so it was impossible to perfectly line up all the shots. However, as the impact only lasts a fraction of a second (as shown by videos of the event), it is guarantee that these images do overlap at least during the time of the flash (or parts of it). Especially since there is only one flash recorded on the eclipsing Moon in the entire 2019, and only one other impact event during the lunar eclipse has been recorded so far.

Knowledge about the meteor impact:

- Impact of this size is impossible to predict. Therefore nobody knew about it before. As it turns out, meteor impacts DURING a total lunar eclipse is quite rare. All the photographers who captured it did not know about it, and most likely they were not even aware of it happening during capture. It was only after the impact became viral on the internet that they started looking to see if they had captured it. Luckily enough, since it was a rather rare and fortuitous event, many tried to submit it to APOD, which is how we were able to gather so many of these rare images.

Rotation:

- "Up" in space is rather tricky. For most of us Earthlings we refer to whichever direction that is perpendicular to the horizon as "Up". Therefore the notion of "Up" will depend on latitudes. However, for telescopes that do not see the horizon this notion means very little. Since "Up" will vary a lot depending on the latitude and time, I opted to go for a more universal "North" in orienting this picture.

Background Stars & Composite:

- To create this composite, first I calculate the angular size of each pixel for each image, as each images were taken by different focal length and different sensor. Then I apply scaling to each image so that it's all on the same angular scale. Then it was a matter of matching background stars so they all lined up. The background stars were indeed the ones that came with the individual photos (in fact, stars in each images were combined with lighten mode on photoshop). If you look at the lower left of the image you would not be seeing any stars there, simply because no photo overlap in that region. I just filled it with a blank space. As someone else already mentioned, those "BD" are star names.

Libration:

- Libration is there, but it's small and very subtle. One way you can think of Libration is that the center part of the Moon is 1,737 km closer than the edge so it has slightly less parallax compared to the edge (in fact, it has about 4% smaller parallax angle). However, as it turns out, human eyes are really good at detecting parallax as that's what we do all the time. If you use cross-eye 3D technique on any two sufficiently far away pair you can actually see a spherical moon popping out with your own eyes! However, this technique might be tricky to do for most people. Alternatively, you could also put two images side by side on a VR (or a smartphone with the VR headset) and see it yourself as well.
Last edited by Pon on Thu Feb 06, 2020 4:18 pm, edited 1 time in total.

Pon
Ensign
Posts: 19
Joined: Thu Jan 26, 2012 10:36 am

Re: APOD: Lunar Eclipse Perspectives (2020 Feb 05)

Post by Pon » Thu Feb 06, 2020 4:16 pm

A bonus note to point out: If you trace all the moon images as they appear against the background stars, they happen to trace out a rough geographical map of the Earth as seen from the Moon during the impact! (Albeit the map would be inverted)
Screen Shot 2020-02-06 at 11.22.40 PM.png
You do not have the required permissions to view the files attached to this post.

User avatar
neufer
Vacationer at Tralfamadore
Posts: 17525
Joined: Mon Jan 21, 2008 1:57 pm
Location: Alexandria, Virginia

Re: APOD: Lunar Eclipse Perspectives (2020 Feb 05)

Post by neufer » Thu Feb 06, 2020 6:19 pm

Pon wrote:
Thu Feb 06, 2020 4:16 pm

A bonus note to point out: If you trace all the moon images as they appear against the background stars, they happen to trace out a rough geographical map of the Earth as seen from the Moon during the impact! (Albeit the map would be inverted)
Yes...the map would be inverted top to bottom...but not left to right.

Is that for the same reason that mirrors invert left to right...but not top to bottom :?:
Art Neuendorffer

Pon
Ensign
Posts: 19
Joined: Thu Jan 26, 2012 10:36 am

Re: APOD: Lunar Eclipse Perspectives (2020 Feb 05)

Post by Pon » Thu Feb 06, 2020 11:53 pm

neufer wrote:
Thu Feb 06, 2020 6:19 pm
Pon wrote:
Thu Feb 06, 2020 4:16 pm

A bonus note to point out: If you trace all the moon images as they appear against the background stars, they happen to trace out a rough geographical map of the Earth as seen from the Moon during the impact! (Albeit the map would be inverted)
Yes...the map would be inverted top to bottom...but not left to right.

Is that for the same reason that mirrors invert left to right...but not top to bottom :?:
It is indeed mirror imaged.

On a side note, mirrors are actually inverted along both axes. The reason we only perceive them to be inverted only left to right...but not top to bottom is actually due to our definition. We humans tend to keep what's "up" straight up (thanks to gravity) and then "right" would be going clockwise from that. If we had started from "right" and going counterclockwise to find "up", we would find that it's the top to bottom that was inverted instead.

In this image, you could think of it in terms of the cardinal direction in the sky instead. In astronomy, the sky has cardinal directions inverted, same way with this picture. It's only because we like to keep "N" straight "up", that we see "E" and "W" inverted instead.

tracychess
Asternaut
Posts: 1
Joined: Fri Feb 07, 2020 1:45 am

Re: APOD: Lunar Eclipse Perspectives (2020 Feb 05)

Post by tracychess » Fri Feb 07, 2020 2:37 am

I was surprised that an article titled "perspectives" do not show any from the equator or below. The perspective from Peru or Buenos Aires is totally different for a reason not discussed. I do wonder if anyone below the equator captured the strike.
Tracy Kolenchuk

Pon
Ensign
Posts: 19
Joined: Thu Jan 26, 2012 10:36 am

Re: APOD: Lunar Eclipse Perspectives (2020 Feb 05)

Post by Pon » Fri Feb 07, 2020 3:08 am

tracychess wrote:
Fri Feb 07, 2020 2:37 am
I was surprised that an article titled "perspectives" do not show any from the equator or below. The perspective from Peru or Buenos Aires is totally different for a reason not discussed. I do wonder if anyone below the equator captured the strike.
Tracy Kolenchuk
In the image I ignored the horizon orientation (Horizon doesn't really matter for object floating in space anyway, see explanation in post above), so whether an observer is below equator or not would not matter in this case.

User avatar
neufer
Vacationer at Tralfamadore
Posts: 17525
Joined: Mon Jan 21, 2008 1:57 pm
Location: Alexandria, Virginia

Re: APOD: Lunar Eclipse Perspectives (2020 Feb 05)

Post by neufer » Fri Feb 07, 2020 4:19 am

Pon wrote:
Thu Feb 06, 2020 11:53 pm
neufer wrote:
Thu Feb 06, 2020 6:19 pm
Pon wrote:
Thu Feb 06, 2020 4:16 pm

A bonus note to point out: If you trace all the moon images as they appear against the background stars, they happen to trace out a rough geographical map of the Earth as seen from the Moon during the impact! (Albeit the map would be inverted)
Yes...the map would be inverted top to bottom...but not left to right.

Is that for the same reason that mirrors invert left to right...but not top to bottom :?:
It is indeed mirror imaged.

On a side note, mirrors are actually inverted along both axes. The reason we only perceive them to be inverted only left to right...but not top to bottom is actually due to our definition. We humans tend to keep what's "up" straight up (thanks to gravity) and then "right" would be going clockwise from that. If we had started from "right" and going counterclockwise to find "up", we would find that it's the top to bottom that was inverted instead.

In this image, you could think of it in terms of the cardinal direction in the sky instead. In astronomy, the sky has cardinal directions inverted, same way with this picture. It's only because we like to keep "N" straight "up", that we see "E" and "W" inverted instead.
Thanks for the reply (although it was intended as a thought experiment for the general reader).

When "observed" from the center of the Earth laser beams from these 7 observation locations "passing through the Moon" would produce a photographic image (of the 7 observation locations onto the background star-field) that was rotated 180º around the Earth-Moon axis.

I once had a minor role in the Apollo retroreflector experiment. If one of those retroreflectors was large enough for us to actually observe the Earth's reflection we would observe a reflected Earth similarly rotated 180º around the Earth-Moon axis.

Of course we don't map the Earth from the POV of its center but rather from the POV of space with a corresponding rotation of 180º around the Earth's own axis (or in this case around the Moon's own axis). Hence left-right gets corrected in the mapping but not N-S.
Art Neuendorffer

User avatar
RJN
Baffled Boffin
Posts: 1574
Joined: Sat Jul 24, 2004 1:58 pm
Location: Michigan Tech

Re: APOD: Lunar Eclipse Perspectives (2020 Feb 05)

Post by RJN » Wed Feb 12, 2020 5:02 pm

Due to an email problem, the last intended line of this APOD's text was not originally included. This line is:
With the simultaneous observations made by independent amateur astronomers across the globe, a group of astronomers were able to use their citizen-science images to narrow down the location, orbit, and energy of this rare event.
This line has now been appended to the main NASA APOD. I apologize for the oversight. - RJN

longtry
Ensign
Posts: 34
Joined: Tue Dec 11, 2018 6:59 am

Re: APOD: Lunar Eclipse Perspectives (2020 Feb 05)

Post by longtry » Thu Oct 15, 2020 2:40 am

1 of the links in the APOD text points to a research letter where they concluded that the rock was about 27kg and made a hole around 9m. Since then, have spacecrafts taken picture of the scene? Especially when the crater was still fresh?