Thursday, June 30, 2016

Amazing facts about Jupiter

Jupiter is the largest planet in the solar system, a gas giant of Hydrogen and Helium with some Ammonia in the upper beautiful clouds layer (and small amounts of other things). Juno spacecraft will arrive to Jupiter on the symbolic day of the 240th independence day of the USA and enter into an orbit around it. Here are some interesting facts about Jupiter.

Jupiter - Hubble telescope - NASA
Jupiter - Hubble telescope - NASA
Jupiter is massive
Jupiter is not only big, it is massive as well. You can say that the entire mass of the solar system is divided in the following way. 99% of the mass is the Sun, 2/3% of the mass belongs to Jupiter and all the rest is just 1/3% (This division is not scientifically accurate but is suitable enough for our needs). Jupiter mass is two times the mass of everything else in the solar system except the sun, and this mass influences the sun and cause it to wobble a little in its orbit. The barycenter of the sun-Jupiter system is well OUTSIDE the sun. 

Jupiter can't become a star
Although Jupiter is huge it is still far too little to become a star and it requires to add at least twenty times its own mass or even more to become so. Adding just little more mass, two-three times as its current mass, will not make Jupiter bigger but will make it denser, but not dense enough to start nuclear fission. 

You can see Jupiter in daylight
Jupiter is seen clearly from Earth. It is the brightest object in the sky after the sun, moon and Venus. Under best conditions, Jupiter can be seen during the day. It requires some practice but possible.

Jupiter has lots of visitors
The first spacecrafts to visit Jupiter were the Pioneer missions in the early seventies followed by both Voyagers missions in 1979. It took some time for the next visitor, Ulysses in 1992 which was on her way to explore the sun poles and got to Jupiter in order to use its gravity to change orbit. Galileo in 1995 was the first spacecraft to orbit Jupiter for a long period and ended in a brave crash into its atmosphere. Cassini just said a quick hello in 2000 on her way to Saturn and New-Horizons also "stopped by" for a cup of coffee on her way to Pluto. Juno mission will be an interesting long mission around Jupiter.

Jupiter protects us
The great mass of Jupiter helps to keep the solar system clean and remove hazards such as asteroids and comets from the inner solar system. Sometimes Jupiter fell asleep during his watch and the dinosaurs are still angry about him, but without Jupiter, things will be worse. Jupiter also gets the bullet for us from time to time. In 1994 Shoemaker-Levy comet crashed into Jupiter and left some scars on it for about a year. Not long ago an amateur astronomer got another small crash on video:

Jupiter is not alone
Jupiter has lots of company. 67 moons so far and probably plenty of smaller ones. Its four largest moons were discovered in 1609 by Galileo. The largest moons - Io, Europa, Ganymede, and Callisto - are bright enough to be seen by the naked eye, but Jupiter is too close to them and prevents that. Even a small binoculars will show the moons.

It is best to keep some distance from Jupiter
Ask Io. A small moon and one that its planet has enormous influenza on its structure. Io is smaller than our moon and the distance from Jupiter's center to Io is around 400,000 km. To be so close to Jupiter is not a good idea. Strong gravitational forces cause earthquakes and volcanic activity and made Io look like... Like what actually?

Io - Nasa JPL
Io - Nasa JPL
Jupiter helped to measure the speed of light
The Danish astronomer Ole Romer noticed a difference between the predicted time and actual time of Io's (The cheese ball from above) eclipses behind Jupiter. His idea was that these difference derived from the changes in Earth-Jupiter distance and that the light has a speed. He gave a value of 220,000km/sec which is around 76% of the actual value, a really good approximation!

Jupiter can suddenly Vanish from our view
Well, not that suddenly but the moon can occult Jupiter (just like any other planet). It is a rare event and here is a short video I took several years ago.

Wednesday, June 1, 2016

How to remove light pollution with "Blur and Subtract"

How to remove or at least reduce light pollution is a frequently asked question. The "Blur and Subtract" technique is a process which I use to reduce light-pollution on my astro-photography images. I live in an urban area and the skies are never black. Of course the best thing is to travel to a darker place, but most of the time that is not possible. I wanted to have a quick method to remove some of the light pollution without working too much on the computer. As it turned out this method provides very interesting results in both daylight and night photos.

The name of the technique "Blur and Subtract" speaks for itself and has three major steps:
  1. Take your desired photo (Photo 1)
  2. Take the same photo but use manual focus to blur the image as much as possible (Photo 2)
  3. Subtract (Photo 1 - Photo 2)

That is all, but if you are not familiar with any photo processing software continue to the detailed tutorial or watch this two minutes demonstration video.

Why the "Blur and Subtract" method reduces light pollution?

This method works well for light pollution since in Photo 1 the focus is usually set to infinity and in Photo 2 it will be set to just to a few cm, diffusing every star but the brightest into the background. Subtracting the background (Which is usually yellow/brown/green) will give a black background with the original stars. If you forgot to take photo 2 you can use the Blur function in a software but I think that taking a second photo is a better approach.
This method turns the following photo - Iridium Flare in Corona Borealis (Northern Crown)
Iridium Flare in Corona Borealis
Iridium Flare in Corona Borealis - With light pollution
Into this one
Iridium Flare in Corona Borealis - Light pollution removed
Iridium Flare in Corona Borealis - Light pollution removed
Which is much darker!

But you can use this method even if you include terrestrial objects and even in daylight. Strong lights will diffuse but will still be noticeable and the entire image will look surrealistic.
Here is an example. What we see here is an Iridium flare near the constellation Cygnus (Swan), and the entire summer triangle including Vega at the top and Altair at the bottom-right. The photo was taken with a wide lens (16mm). The method will work better for longer focal lengths as the change of the focus will diffuse the strong lights better.

Photo 1 - proper focus
Photo 1 - proper focus
This is the second photo. The flare is already gone which is even better for us (it improves the subtraction). The stars disappeared (except the really bright ones) and the city lights looks  bigger. 
Photo 2 - Focus to nearest point possible
Photo 2 - Focus to nearest point possible

And this is the result of the subtraction and some other processing. You might need to tilt the monitor a little bit and since it is very black a good quality monitor is required.

I applied some more fixes to the photo such as:
  1. Remove the diffused bright stars (Vega and Deneb) - Single click of the Spot Heal tool around each star.
  2. Remove the strayed light in the bottom-right caused by forgetting to cover the eyepiece during the long exposure - again one of the Heal tools did the trick.
  3. Many crops (just the flare, just the summer circle, just the flare and the buildings, etc.) but here I show the full image.
The sky is much darker and probably some faint stars are not shown (more fine tuning in software is possible if you desire), but what is more incredible is what happened to the buildings.

Detailed Tutorial

If you need an online free tool for this purpose you can use Pixlr. Here are the exact steps. The steps are identical for other software such as Photoshop or Lightroom but not everyone has them. Pixlr is a strong free alternative and has many features. However it might reduce the resolution of the image (There is a stronger desktop version but it is not free to use).

1. Browse to pixlr site, choose "Open image from computer" and select your first photo (the photo with the correct focus).
Open PXLR site
Open Pixlr site
2. The photo will appear on the screen. To open the second blur photo (Photo-2) as a new layer, go to the Layers menu and choose "Open image as layer", select the second photo.
Choose open image as layer
Choose open image as layer
 3. Check the layer window and press the "Toggle layer setting" button as displayed in the image below. This displays a dialog box with the options we need for the subtract operation.
Press Toggle layer setting button
Press Toggle layer setting button
 4. In the mode option choose "Difference".
Choose "Differnce" as mode
 5. That's it. If you need to process the image further, do it now or simply save your file with a new name as a JPEG or preferably PNG file.
Save the result file
Save the result file

More examples

Here is another example. The time is just after sunset but skies are still blue. Here is the result after I cropped most of the sky.

And another interesting application on this royal ponciana blooming tree
 royal ponciana blooming tree
 royal ponciana blooming tree
 Into this strange colors.
 royal ponciana blooming tree
 royal ponciana blooming tree

And a photo of the sun (Warning: photographing the sun requires special filters. Never look directly at the sun!). The sun is very bright so blurring it will create a larger and dimmer image of the sun (a red giant lookalike)) and create an interesting image.
Double sun
Double sun