With a time lapse video in the winter and in the summer, I could cover the whole northern sky: When it’s getting bright in one of the videos, it starts to get dark in the other one. Probably best to watch fullscreen:
The reason behind is between the two videos, the earth has done half a round around the sun and so at midnight, when looking at Polaris, one looks from opposite directions.
Recently I was made aware about an impressive moon halo, also know as moon dog. I have seen light versions of it before, but not as clear.
It happens when a layer of ice crystals forms high in the atmosphere. Each of the crystals then acts as a prism, refracting the light into a certain way. It’s a similar (and yet not) effect like when a rainbow forms. And actually a moon halo also has a colour gradient, the inner bit is red, the outer bit is blue. However, in my image that is not visible, a longer exposure time would have been good. Next time 🙂
Instead, what I did was recording a time lapse for 30 minutes:
While some clouds move very quickly, the only apparent change of the halo is caused by earth’s rotation (the moon and halo moving along the image). This also made clear, what are stars and what are optical effects/defects from the lens. Right to the moon are Castor and Pollux of constellation Gemini, and below the moon, next to the tree, is Procyon. All stars fainter than magnitude 2 are invisible due to the scattered moon light (which itself is just reflected sun light).
More information can be found on the Wikipedia article about moon halos: https://en.wikipedia.org/wiki/22%C2%B0_halo
Two and a half years earlier a got a glimpse of a sun halo:
Nicer examples of sun halos can be found on Wikipedia: https://en.wikipedia.org/wiki/Halo_(optical_phenomenon)
Create a time lapse from individual images: https://ronnyerrmann.wordpress.com/2022/02/12/commands-to-create-time-lapse-videos-from-individual-frames/
In a podcast I listened to yesterday the experiment was discussed, using normal ice cubes. And they suggested to repeat the experiment with dyed ice cubes or dyed water. Yesterday I prepared the ice cubes and today did the experiment.
Some words about the preparation: Dissolving salt creates heat, hence I allowed for time so that the water could reach room temperature again. Therefore, the interesting bit only starts after a minute into the time lapse, or 20 minutes in real time.
The ice cubes start melting immediately, both distribute a bit of blue water to their glasses. However, the difference becomes visible very quickly: In the fresh water a constant stream of blue water flows to the bottom of the glass. In the salt water glass the blue melt water from the ice cube creates a layer on the top of the glass. The ice cube swims in this cold water, is isolated from the warm water, and hence survives about twice as long.
The reason of the different behaviour is related to density. A cold liquid has a higher density than a warm liquid, and hence sinks to the bottom (in the same way that a piece of metal has a higher density than water, or humans have a higher density than air). However, dissolving salt in water increases the density of that water, and the saltwater has a higher density than the cold water from the ice cube.
When the experiment was described, I guessed wrong. Using salt to melt ice on streets, I thought the ice cube in the salt water will melt quicker, due to a chemical reactions. However, as the salt is already dissolved, no heat can come from destroying the crystal structure (and that would be a physical reaction and not a chemical reaction anyway).
I didn’t want to show an hour long video on youtube, hence speed up certain parts of the video. For this I used the free ffmpeg tool on a Ubuntu 20 laptop. Running the code below took about 10 Minutes on my Laptop:
ffmpeg -i ../orig.mp4 -ss 00:00:00 -to 00:00:05 -c copy temp.mp4 && ffmpeg -i temp.mp4 -r 16 -filter:v "setpts=0.10*PTS" output_01.mp4 && rm temp.mp4 ffmpeg -i ../orig.mp4 -ss 00:00:05 -to 00:00:27 -c copy temp.mp4 && ffmpeg -i temp.mp4 -r 16 -filter:v "setpts=0.50*PTS" output_02.mp4 && rm temp.mp4 ffmpeg -i ../orig.mp4 -ss 00:00:27 -to 00:00:54 -c copy temp.mp4 && ffmpeg -i temp.mp4 -r 16 -filter:v "setpts=0.10*PTS" output_03.mp4 && rm temp.mp4 ffmpeg -i ../orig.mp4 -ss 00:00:54 -to 00:01:12 -c copy temp.mp4 && ffmpeg -i temp.mp4 -r 16 -filter:v "setpts=0.50*PTS" output_04.mp4 && rm temp.mp4 ffmpeg -i ../orig.mp4 -ss 00:01:12 -to 00:03:05 -c copy temp.mp4 && ffmpeg -i temp.mp4 -r 16 -filter:v "setpts=0.10*PTS" output_05.mp4 && rm temp.mp4 ffmpeg -i ../orig.mp4 -ss 00:03:05 -to 00:03:12 -c copy temp.mp4 && ffmpeg -i temp.mp4 -r 16 -filter:v "setpts=0.33*PTS" output_06.mp4 && rm temp.mp4 ffmpeg -i ../orig.mp4 -ss 00:03:12 -to 00:03:20 -c copy temp.mp4 && ffmpeg -i temp.mp4 -r 16 -filter:v "setpts=0.10*PTS" output_07.mp4 && rm temp.mp4 ffmpeg -i ../orig.mp4 -ss 00:03:20 -to 00:19:50 -c copy temp.mp4 && ffmpeg -i temp.mp4 -r 16 -filter:v "setpts=0.01*PTS" output_08.mp4 && rm temp.mp4 ffmpeg -i ../orig.mp4 -ss 00:19:50 -to 00:20:10 -c copy temp.mp4 && ffmpeg -i temp.mp4 -r 16 -filter:v "setpts=0.10*PTS" output_09.mp4 && rm temp.mp4 ffmpeg -i ../orig.mp4 -ss 00:20:10 -to 00:20:40 -c copy output_80.mp4 ffmpeg -i ../orig.mp4 -ss 00:20:40 -to 00:21:00 -c copy temp.mp4 && ffmpeg -i temp.mp4 -r 16 -filter:v "setpts=0.15*PTS" output_81.mp4 && rm temp.mp4 ffmpeg -i ../orig.mp4 -ss 00:21:00 -to 00:27:11 -c copy temp.mp4 && ffmpeg -i temp.mp4 -r 16 -filter:v "setpts=0.05*PTS" output_82.mp4 && rm temp.mp4 ffmpeg -i ../orig_02.mp4 -ss 00:00:00 -to 00:07:20 -c copy temp.mp4 && ffmpeg -i temp.mp4 -r 16 -filter:v "setpts=0.05*PTS" output_83.mp4 && rm temp.mp4 ffmpeg -i ../orig_02.mp4 -ss 00:07:20 -to 00:07:27 -c copy temp.mp4 && ffmpeg -i temp.mp4 -r 16 -filter:v "setpts=0.15*PTS" output_84.mp4 && rm temp.mp4 ffmpeg -i ../orig_02.mp4 -ss 00:07:27 -to 00:07:42 -c copy temp.mp4 && ffmpeg -i temp.mp4 -r 16 -filter:v "setpts=0.50*PTS" output_85.mp4 && rm temp.mp4 ffmpeg -i ../orig_02.mp4 -ss 00:07:42 -to 00:07:50 -c copy temp.mp4 && ffmpeg -i temp.mp4 -r 16 -filter:v "setpts=0.15*PTS" output_86.mp4 && rm temp.mp4 ffmpeg -i ../orig_02.mp4 -ss 00:07:50 -to 00:27:11 -c copy temp.mp4 && ffmpeg -i temp.mp4 -r 16 -filter:v "setpts=0.05*PTS" output_87.mp4 && rm temp.mp4 ffmpeg -i ../orig_03.mp4 -ss 00:00:00 -to 00:05:11 -c copy temp.mp4 && ffmpeg -i temp.mp4 -r 16 -filter:v "setpts=0.05*PTS" output_88.mp4 && rm temp.mp4 ffmpeg -i ../orig_03.mp4 -ss 00:05:11 -to 00:05:33 -c copy temp.mp4 && ffmpeg -i temp.mp4 -r 16 -filter:v "setpts=0.20*PTS" output_89.mp4 && rm temp.mp4 for f in $(ls output*.mp4); do ffmpeg -i $f -c copy -bsf:v h264_mp4toannexb -f mpegts $f.ts done CONCAT=$(echo $(ls *.ts) | sed -e "s/ /|/g") ffmpeg -i "concat:$CONCAT" -c copy -bsf:a aac_adtstoasc VID_20220224_094623206.mp4 rm *.ts
12 Feb 2022 – Ronny Errmann
Some of the time lapses can be found on youtube: Youtube Channel Ronny Errmann, for example an 8 hour time lapse of the night sky over La Palma. If you modify your images before creating a video, creating a working directory and copying the images into that will safe you from accidentally destroying the originals.
mencoder mf://*.jpg -mf fps=24:type=jpg -noskip -vf scale=1156:868 -of lavf -lavfopts format=mp4 -ovc x264 -sws 9 -x264encopts nocabac:level_idc=30:bframes=0:bitrate=16384:threads=auto:turbo=1:global_header:threads=auto:subq=5:frameref=6:partitions=all:trellis=1:chroma_me:me=umh -o output.mp4
The following settings should be adapted to your images:
mogrify -resize 1156x868 IMG_20220212*.jpg
mogrify -rotate 90 -background black *.jpg
To remove useless bits from the image, the values are the new size + start positions
mogrify -crop 3515x2541+142+199 *.jpg
Sometimes it’s nice to see the real time running in the time lapse, for this the exif information can be used. In the example the modified images will be copied into “prefix_<original name>”
for img in *jpg; do convert "$img" -gravity SouthEast -pointsize 70 -fill white -annotate +30+30 %[exif:DateTimeOriginal] "prefix_""$img"; done
The following options can be changed:
For example, when taking night images and the video is too dark.
mogrify -modulate 200 *.jpg
6 Feb 2022 – Ronny Errmann – last modified on 31 March 2022
Some useful bits which helped me to make the time lapse videos I recorded ready to be published on youtube: Youtube Channel Ronny Errmann
For when the phone was upside down during the recording.
ffmpeg -i input.mp4 -c copy -metadata:s:v rotate="180" output.mp4
When personal information is in an area of the video.
ffprobe -v error -select_streams v:0 -show_entries stream=width,height -of csv=s=x:p=0 input.mp4
ffmpeg -i input.mp4 -filter:v "crop=1280:600:0:120" output.mp4
To keep 00:00:00 to 00:01:22, because afterwards only night was recorded as work had to be finished first.
ffmpeg -i input.mp4 -ss 00:00:00 -to 00:01:22 -c copy output.mp4
When you notice at the end of a time lapse that the sky is still amazing and you recorded a second one.
Several lines of shell script, run with sh:
for f in $(ls input*.mp4); do ffmpeg -i $f -c copy -bsf:v h264_mp4toannexb -f mpegts $f.ts done CONCAT=$(echo $(ls *.ts) | sed -e "s/ /|/g") ffmpeg -i "concat:$CONCAT" -c copy -bsf:a aac_adtstoasc output.mp4 rm *.ts
Use Version 2 if this fails with:
Codec 'mpeg4' (12) is not supported by the bitstream filter 'h264_mp4toannexb'rm -f mylist.txt; for f in input*.mp4; do echo "file '$f'" >> mylist.txt; done ffmpeg -f concat -safe 0 -i mylist.txt -c copy output.mp4 rm mylist.txt
You took a time lapse, but the viewers are bored, because changes are too small. Time to speed the video up.
ffmpeg -i input.mp4 -r 16 -filter:v "setpts=0.50*PTS" output.mp4
0.5*PTS mean twice the speed, 0.1*PTS would mean ten times the speed, and 2*PTS would mean half the speed.
ffmpeg -y -i input.mp4 -vf scale=480:-2,setsar=1:1 -c:v libx264 -c:a copy output.mp4
The 480 gives the horizontal resultion and the heigh is calculated by keeping the same aspect ratio.
Ronny Errmann 