Supermaan supermanie

Wat is er nou zo bijzonder aan zo’n supermaan?
Niet zo veel hoor, al doet de media dit wel voorkomen. ‘Supermanen’ komen regelmatig voor. Bijna elk jaar is er wel eentje.
Ook is het geen officiële wetenschappelijke benaming. Het is ooit bedacht door een astroloog (niet te verwarren met een astronoom, een universitair geschoolde sterrenkundige!).

Wat is een supermaan?
De maan draait niet in een perfecte cirkel rond de Aarde maar in een ellips.
Dit betekent dat de maan nooit op een constante afstand van de Aarde staat.
Als de maan in zijn ellipsbaan het dichtst bij de Aarde komt dan noemt men dit het perigeum.
Een supermaan is pas een supermaan als het op bovenstaand moment ook nog eens een volle maan is.
De maan staat dan ongeveer 7% dichter bij de Aarde dan normaal en reflecteert dan ook nog eens 30% meer zonlicht.
Klinkt spannend maar je ziet niet echt het verschil met een normale volle maan die ook al een flinke bak licht geeft.

Links, de maan in perigeum en rechts in apogeum. (foto:NASA)
Links de maan in perigeum en rechts in apogeum. (foto: NASA)

Het moment dat de maan het verst weg staat noemt men het apogeum. Niemand heeft het dan over een minimaan.

Kortom, wanneer de media weer bol staat van supermanen of varianten hiervan (een superbloedmaan als er toevallig ook een maansverduistering plaatsvindt), geniet er maar gewoon lekker van en negeer de poeha.

Wat getalletjes
Gemiddelde afstand naar de maan: 384.400 kilometer
Gemiddelde afstand naar de maan tijdens perigeum: 360.000 kilometer
Gemiddelde afstand naar de maan tijdens apogeum:  405.000 kilometer

Een mooi overzicht van supermanen in de 21e eeuw vind je op deze pagina. De lijst is gesorteerd op afstand, niet op jaartal.

De Mercurius overgang van 9 mei 2016

Onbewerkte videobeelden van de Mercuriusvergang op 9 mei 2016.
Er stond veel wind wat de reden is van het schuddende beeld 🙂
Waargenomen in Utrecht door een Celestron C6 SCT telescoop, een zelfgemaakte zonnefilter en een Philips ToUCam webcam.

De planeet Saturnus

Saturnus vanuit Toscane

Zo zag de planeet Saturnus er uit op 11 juni 2015 vanuit een broeierig Lajatico (Toscane, Italië).
De seeing was niet echt om over naar huis te schrijven door de vele luchttrillingen van de warmte dus dit was het beste wat ik uit de stack kon krijgen.
De Cassini scheiding is in de ring te zien en ook iets van een wolkenband op het planeet oppervlak.

De gebruikte apparatuur:
Celestron C6 SCT
2,5x Barlow
Philips SPC840 webcam

Ik denk dat ik toch maar eens moet gaan investeren in een betere camera 🙂


Capturing SAT24 satellite images to create an animation

During the solar eclipse on March 20th 2015 it was nothing but clouds over here in The Netherlands.
So besides following the eclipse on TV I also watched the satellite images on the SAT24 site to track the Moon’s shadow over the continent.
I got the idea to create a small bash script that downloads the satellite images every X minutes in a separate directory.
Those images can be stitched together to create a nice movie.

So, here’s the code:

CURRENTIMAGE=$(date +"%Y%m%d%H%M")

wget -O $TMPDIR/temp.jpg "$INFRARED"

MD5NEW=`/usr/bin/md5sum $TMPDIR/temp.jpg | cut -d ' ' -f 1`
MD5OLD=`/usr/bin/md5sum $TMPDIR/prev.jpg | cut -d ' ' -f 1`

if [ "$MD5NEW" != "$MD5OLD" ]; then
cp $TMPDIR/temp.jpg $TMPDIR/prev.jpg

It’s pretty straight forward.
The image file name is the current date and time and a new image is downloaded using wget.

The only thing that needs an explanation is the md5sum stuff.
Sometimes it happens that the script downloads a image from a few minutes ago and not the current one.
That means that most of the time it’s an image you already have.
I guess this has something to do on the Sat24 side: web servers not in sync or load balancers that don’t balance load.
With md5sum you create a MD5 hash which is ‘unique’.
If the new image has the same MD5 has as the previous image, this new image can be discarded because you’ve already downloaded it.

To make this script run automatically, simply add it to the crontab (I’m using the cron of user pi on my Raspberry Pi here):

<code>*/4 * * * * /home/pi/sat24/</code>

I use intervals of 4 minutes but you can tune that if you like.
Oh, and do not for get to turn on the execute bit of your script.

Okay, you’ve been running this script for a couple of days and you’ve collected hundreds of images.
Now it’s time to stitch them together and make an animation!

Thanks to a great command line tool called avconv (previously known as ffmpeg), you can create a movie file using separate images:

cat images/*.jpg | avconv -f image2pipe -c:v mjpeg -i - -r 25 -map 0 -s 1280x780 -filter:v "setpts=4.0*PTS" out.mp4

Err…yes! It’s that simple!
Just cat the files and pipe them into avconv.
The -s 1280×780 parameter creates a 720p HD video file.
The -filter:v “setpts=4.0*PTS” parameter slows the playback rate down because 0therwise the animation goes a bit too fast. You can fiddle with the number to your taste.
The video created is called out.mp4 which you can rename if you want, of course.

And this is the result:

Some double images might be downloaded once in a while, which you can delete by yourself by wading through the images directory.
Or you could write a script that checks and deletes duplicates for you.

Introducing: ScopeHunter

This is something I was busy with the last couple of months: ScopeHunter.

It’s a internet search engine for optical instruments. It checks quite an amount of auction- and biddingsites and internet forums related to astronomy and photography with a buy/sell section.

If you’re looking for a telescope, microscope, webcam or a DSLR camera, you don’t have to search the web yourself.
ScopeHunter does all the work for you. You can even subscribe to a RSS feed to get regular search results.

Happy hunting! 🙂

Astronomy YouTube channels worth checking

The years when YouTube was only a place where you could only find videos from kittens and fail videos containing people with skate boards crashing into fences are long gone.
Okay, these videos are still uploaded but things really got rolling when they introduced channels.
Since then numerous channels about all kinds of topics, like astronomy, exist.

For me, YouTube is a great source of information about my hobby.
In the last couple of years I subscribed (and unsubscribed) a lot of astronomy related channels and I would like to share a couple of them, which I really like, with you.

If you have another tip for a cool astronomy YouTube channel to check out, please put them in the comments.

Eyes on the Sky
Eyes on the Sky by amateur astronomer David Fuller brings you a weekly, 5 minute show about what’s up in the sky for this week.
Besides that he gives tips how to star hop to certain objects and occasionally you’ll see him wearing a wig for Astronomy Theatre 🙂
A recommended channel for the novice but also for advanced amateur astronomer.
Oh, and don’t forget to check his website for background information and links to videos with astronomy tips like alignment, getting orientated and sun observation to name a few.

Universe Today
This channel, hosted by Fraser Cain, publisher of the astronomy and space news site Universe Today, covers every week a astronomy related topic.
Topics vary from How big is the Solar System to What is a Quasar?

Space Fan News
A weekly news show hosted by Tony Darnell (and sometimes by Scott Lewis) recapping the week with astronomy and space news.
Complex topics are explained in a simple, almost in layman terms, and entertaining manner.

Deep Sky Videos
This is one of the many high quality YouTube channels maintained by video journalist Brady Haran.
Deep Sky Videos covers the objects from the Messier catalogue, the telescopes in Chile and La Palma and other astronomy related topics.
Deep sky objects are explained by professional astronomers so you know what you’re looking at, next time you point your scope into its direction.

Astronomy Shed
Not that active as it was before, Astronomy Shed hosted by Dion Heap gives you the latest astronomy gadgets and explains you stuff you need to know about your telescope.
Topics like polar alignment and mirror collimation are explained in detail.
This channel really got me going again after my 20 years astro break.

Houston Haynes
I found this channel, hosted by Houston Haynes, when I was about to buy my Coronado PST solarscope.
Videos with valuable information about solar observation and solar imaging using a webcam.

Miscellaneous channels
Here are some channels where I’m subscribed to which aren’t astronomy specific but I really want to share with you.

Sometimes scientific, sometimes philosophical and sometimes food for thought: VSauce by Michael Stevens.

Do you like those BBC documentaries or old The Sky at Night episodes? Check out UKAstronomy.

The documentary channel for all your Space & Universe, Science & Technology and Nature documentaries in HD: The HDdocumentaryChannel.

Making a cheap dew controller using a LED dimmer

After short circuiting a 12 Volt hair dryer which I used for dew prevention at a starparty a few months ago, I thought it was time to get a real dew controller and a dew heater for my scope.
An average dew controller costs more than 100 Euro (or US Dollars) which is, in my opinion, quite expensive for something that only controls voltage between 0 and 12 with a potentiometer.

One or two years ago, ‘rwagter’ a user on the Dutch Astroforum, came up with the idea of using a cheap 12 Volt LED dimmer as a dew controller.
After that I’ve seen numerous dew controllers using this LED dimmer created by people on the Dutch Astroforum and Stargazers Lounge.
I’m not a electronics buff at all, but after reading how people had built their own, I would give it a try.

The dimmer costs about 4 US Dollars each on eBay, and most of the time shipping is free.
After ordering, you’ll need to have some patience because delivery from Hong Kong can take 4 or more weeks.
Just search on eBay for 12 Volt LED dimmer and find the one that resembles the picture above because that’s the one you’ll need for this DIY project.

For my DIY project I’m using 2 dimmers and each dimmer outputs to 2 channels.
You can connect a dew heater on each channel, so in my case I can connect 4 dew heaters.

2x 12 Volt LED dimmer
1x lighter plug for connecting to a powertank
4x RCA chassis mount (female)
2x 5mm red LED (diffuse)
2x LED holders (plastic)
2x 2200 Ohm resistors
1x casing to put it all in
some cable

A soldering iron
A drill to drill holes in the casing
Nice to have: a Multi meter

dewc_componentsThe LED’s and the resistors are not mandatory. I thought it would be fun to see the LED light dim when using the potentiometer 🙂

Total costs (including the 2 dimmers) was 30 Euro.
You can reduce the costs by using only 1 dimmer, a smaller case or just by re-using the dimmer case.
The case and the lighter plug (I bought a fused one) were the most expensive: both around 8 euro.

Building the dew controller is pretty straight forward.
The first 2 connectors on the dimmer are 12 volt input (V- and V+), connectors 3 and 4 are output (V+ and V-).
Power from your power supply goes into the input and the output connects to a RCA connector.
The only thing you need to keep track of, are the + and the – connections.

I’m using 2 channels per dimmer, so if you want to do that too, you’ll have to connect them in parallel.
That’s really it.

If you want to add some LED’s, take a look at this picture (courtesy of Gina/Stargazers Lounge):
ledsThe only thing what’s wrong in this picture, is that the input and output connections of the dimmer are switched.
Got me puzzled for a few seconds.

Here is the result of a Saturday afternoon drilling and burning my fingers by the soldering iron.


Now I’ll have to wait for clear skies and loads of dew 🙂

Remote control your GoTo telescope mount using a Raspberry Pi and SkySafari

SkySafari is a great astronomy app for smart devices like the iPhone, iPad and Android.
The SkySafari Plus and Pro versions add the possibility to remote control your GoTo telescope mount using the special SkyFi adapter.
This adapter sends serial (RS-232) commands, received with a wireless connection, to the handset of the GoTo mount.
Using SkySafari in combination with SkyFi increases the number of objects you can observe and current events in the sky (like comet PANSTARRS at the moment) are found easily this way.

I was wondering if it would be possible to create something like SkyFi using the Raspberry Pi.
And yes, it is possible. Quite easy actually!

What do you need?

  • Raspberry Pi configured with a working network connection (wifi preferred, of course).
  • USB to Serial cable.
  • GoTo telescope mount
  • PC Serial to GoTo handset cable. Shipped with your GoTo mount.
  • SkySafari Plus or Pro
  • Basic Linux knowledge

Now how are we to receive the commands from SkySafari?
This is done by the Serial To Network Proxy (ser2net).

Install ser2net:

sudo apt-get install ser2net

Add the following line, using your favorite text editor, at the end of the ser2net configuration file (/etc/ser2net.conf) which contains the port where ser2net is listening on:

4000:raw:0:/dev/ttyUSB0:9600 NONE 1STOPBIT 8DATABITS

In this case, I chose port 4000. You may choose another port but be sure it is between 1024 and 65535 and does not conflict with any other daemons listening on the same port.

Restart the ser2net service with the new configuration:

sudo /etc/init.d/ser2net restart

Next, configure your telescope in SkySafari.
My setup has a SkyWatcher SynScan GoTo on a EQ3-2 equatorial mount.
Be sure to enter your setup and don’t copy my settings bluntly 😉


The IP address in the picture above corresponds with my Raspberry Pi. Of course, you should enter the IP address of your Raspberry Pi.
Same goes for the listening port. I’m using port 4000.
If you configured a different one for ser2net, enter that one.

After that is done, you should try to connect SkySafari with your mount in the Scope menu and you’re off to go!

Light pollution Cinema

I admit, looking at images made by the ISS crew or time lapse movies made by orbiting satellites of our planet at night can be quite beautiful and stunning.
Back on Earth, that beauty is nothing more than pollution. Light pollution.

Light pollution is becoming a real issue. Astronomers are not the only ones trying to alarm the government because of the disappearing dark skies (when was the last time you saw the Milky Way when you looked up?) but also biologists and people involved with health care blowing the whistle for people to get aware.

A great documentary about light pollution and the search for darkness is The City Dark.
After watching this documentary, I was quite shocked about the impact light pollution has on human health and the habitat of wild animals.

Not a documentary but, as they call it, a public service announcement about the problems and solutions of Light Pollution is Losing the Dark.

Made by the International Dark-Sky Association and Loch Ness Productions, which can watched and downloaded for free on the internet.
Special dome versions (for displaying in a planetarium or observatory) are available too.