Habitable zone of a star

habitable zone of a star. Sounds like a comfy place, right? Well it can be. It is at least on (tiny portion of) Earth which is an example of object in habitable zone. Such a „zone“ is important for astronomers, or maybe it’s just important for headlines in newspapers.

Habitable zone in a Solar System based on luminosity.

Habitable zone is an area around star where we, with quite limited knowledge on this subject, think that life could be. The simplest „definition“ is that it’s the area where satellite (such as planet) would be able to sustain liquid water. We cannot be sure of course if life needs it but it is the case for the one that evolved on Earth.

The true habitable zone is something a bit more complicated. The simplest case of a planet would be one that behaves as a black body, that means that it absorbs all radiation (light for example) regardless of its wavelength. This is immediately just an assumption because such a planet does not exist. Earth just as Uranus or Mercury reflect light, the planet’s albedo describes this. Albedo is an attribute telling us how much object reflects light. 0 means that it is a black body and 1 means that it is white body aka perfect mirror.

There are even more factors that one could consider. For example, when planet has thick atmosphere it can sustain liquid water (and life) even further out from habitable zone on the other hand if that happens to planet like Venus which is already pretty close, you have got hell. If satellite orbits with high eccentricity the conditions are again different.

It’s hard to combine all of this together which results in lot of different outcomes depending what model one picks. Estimates for Solar System are between 0.9 or even 0.6 to 1.3, 2 or 3 astronomical units. In most of them Earth is just on the inner edge. These numbers were pulled from Wikipedia.

When we hear in news that a new exoplanet was found in a habitable zone it might not mean much. This news usually come alongside the information that the planet has similar size that of Earth, it’s not like we could travel there or anything, now we are mostly collecting data and learning.


HZ picture: By Habitable_zone-en.svg: Chewiederivative work: Ignacio javier igjav (talk) – Habitable_zone-en.svg, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=8462897

Problems that we will have to face

Disclaimer: This is my opinion, not advised by anybody, feel free to comment below.


There are two problems that we as humans will have to face. I will write about the two that I think are crucial and only now people start to appreciate them.

The first problem is Global warming. It poses a lot of threats not only to fragile ecosystems but to whole Earth. Some of the effects listed from Wikipedia are: extreme weather, sea level rise, ocean acidification, changes in agriculture, environmental migration and much, much more [1].

Global warming is the first problem that we need to address but in this post, I will concentrate on the next issue on the list. Humanity will eventually die out if we are not able to spread in the Universe [2].

First, we could of course ask the question when we should colonize other planets or even if it is good idea. Let’s take a scenario, when humanity successfully colonizes Mars and at the same time Earth is becoming more inhabitable. At some point, we simply leave it behind, maybe let it rejuvenate without ever learning how to live in a way that does not cause rest of life extinct. What would continue? Maybe we will be able to spread out in the rest of the Solar System and eventually leave it behind. In what state though? And does it even matter if Mars which is right now mostly empty wasteland suffers any damage if it is even possible? Maybe we would change into species that travels the Universe and leaves dead rocks behind? What if we encountered other life out there, would them await the same fate as Earth? We are authors of our own morality and clearly there does not seem to be objective one. Our values change, we are starting to really appreciate our surroundings, the question is, are we fast enough?

Picture of Mount Sharp on Mars, taken by Curiosity rover.


Note: I am aware that there are different things that could happen. I took time today to write shortly out what I thought about one of them.

[1] There are also problems not related to Global warming but are as well very global, for example what are we going to do with plastic.

[2] See also, gamma ray bursts, solar eruptions (big problem but probably no immediate deaths), huge asteroid collisions and other things that would wipe us out.


today I will write about pareidolia a commonly seen phenomena. People often see familiar objects in completely random things, like rocks.

Clearly there is face in the upper middle part of the picture on the left. There is definitely sign of both eyes, of nose and mouth, thats more than one needs to SNice.svgrecognise face in something, consider the following one on the right. Do you see the black thick circle filled with yellow color, two ellipses and curved line extended in the ends? Yeah me too.

The point is that humans are great in recognizing (most often faces) in things that are actually not them. The first picture is photo of region Cydonia which is a area on Mars. It was taken in 1976 by Viking 1 and of course people thought that it was proof for extraterrestrial life! Well if you take enough photos of Mars there is high probability that some of the rocks there will resemble primitive faces.

Pick me! Some may bypass this pear for its blemished skin while others will see how eager it is to please

“I am the evidence of life on Earth, beware!”

Pareidolia does not happen only in images but also in sounds. For example there is a group of people who listen to so-called “ghost boxes” (sub category of ghost hunters). Ghost box is a box that is skimming quickly through radio channels. This creates lot of background noise and static noise with mix of what you can hear from the actual radio.. they say that the ghost can easily communicate through it.

Simplest explanation is of course that they just interpret extremely bad audio as some kind of words, plus if they listen for many hours they will eventually pop out something that will be an answer to your question, here is a link so you can consider for yourself, remember humans are great in interpreting random noise as actual words[1] (skip like 3 minutes for actual talk).

The story of the original Mars picture got stretched over many years. 2 decades after taking the picture, there was much better one taken by Mars Express as you can see below it was just the low resolution of Viking spacecraft.

There are many things that can trick us so it is not best to take the first explanation that we can think of, be sceptical and do not share if you do not know anything about it.


[1]The “answers” should be mostly made by random quotes from songs.

Smiley: By en:User:Mystìc – Originally created by en:User:Mystìc at en:Image:SNive.gif. Vectorized by Psiĥedelisto, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=55079042

Pear: http://www.dailymail.co.uk/femail/article-3280816/What-photos-s-faces-suffer-facial-pareidolia.html


Vacuum decay and Trump

today I want to do a fun post inspired by a meme that I saw some weeks ago on Theoretical Physics Memes. Well here it is:


If you dont understand the joke, its alright, I will explain. If you do understand the joke you can continue reading for the sake of… reading?

Disclaimer: I have not been using disclaimers before but the truth is I am no physicist so I do not claim to actually comprehend this stuff.

So vacuum decay or also false vacuum is the idea that you could die any second. (See I am no physicist)

Basically fields (meaning electromagnetic and other types) want to get into the lowest energy state possible. Also electrons rather like lower energy states to be more stable so, if they have more than they “need”, they will radiate it away in form of photons. Now it is assumed that these fields are either in stable position (lowest energy level) or they might be in metastable position[1], which means that there is energy barrier between the metastable level and stable, if it is “reached over” and the field drops into lower stable or again metastable level it will release energy.

If we were in false vacuum[2] we would just need to reach over the hill to get to true one.

Since particles arise from these fields some new types would appear and Universe in this place would look a bit different inside. The reason why this is connected to the discovery of Higgs Boson is that the mass that it has indicates that we may live in false vacuum, if our physics is right than we could die any moment since the false vacuum is expanding almost at the speed of light.. means we can not know if it is coming on us or not, which also means that you do not need to worry really.

Now you understand the joke though if you are Trump supporter than you do not find it very funny in which case I pity you because it is great joke 😉 [3]


Pic. source: By User:Stannered – Adapted from en:Image:Falsevacuum.png, CC BY 2.5, https://commons.wikimedia.org/w/index.php?curid=1711800

Post source mostly.

[1]They can also be in unstable position but not for long.
[2]The name false vacuum has nothing to do with the vacuum of space.
[3]Proper explanation: it is so bad that Trump is elected, I hope that Universe will end soon, oh hmm.. what is the probability of it happening?

Its about Trappist-1

I noticed that in the last days lot of attention was given to this new exoplanets. Well, I guess I have to stay in the “popular sphere” and follow with my post!

Around star called TRAPPIST-1 also known as 2MASS J23062928-0502285 were found together 7 exoplanets, more on this down in the post.

First the star.

Trappist-1 is very small star in special category L which means that it is a red dwarf. You wont find this category in the normal stellar classification because this one and other are made for brown and red dwarfs and were introduced later on. This of course means that Trappist-1 is not very bright or very hot and NOT visible to naked eye (it has apparent magnitude of 18.8 which is way outside of what human eye can see).

All pictures of these planets are artist’s impression.


The planets were discovered using transit photometry. Method that takes advantage of the planets blocking out some of the star’s light. In 2015 there were 3 discovered already and in February this year, astronomers in Belgium found another 4.

There names are truly beautiful: b,c,d,e,f,g,h (aka. Trappist-1b…)
b,c,e,f,g have similar size to Earth and d,h have radius somewhere between Mars and Earth. e,f,g also orbit in the habitable zone of planet which is an area around the star where liquid water might stay on the surface.

Bit of a problem is that since the planets are so close they receive lot of radiation from Trappist-1 and are also probably tidaly locked, which means that they are facing the star with always the same side, thats what is happening to our Moon too. All of their orbits’ radiuses (semimajor axes) are in matter of few millions of kilometers. For Earth this is 1 AU or 150 millions and for Mercury roughly one third. Their years last few days, for Trappist-1b it is just 1,5 days. Those are definitely some crazy numbers but since we know so little about formation of new life we can not really say how high the probability of something living there is.

NO signals were detected from that direction.


PS: You would have amazing view from the planets since they are so close together.

Source of picture: By NASA/JPL-Caltech – Catalog page · Full-res (JPEG · TIFF), Public Domain, https://commons.wikimedia.org/w/index.php?curid=56513150

Pioneer Anomaly

today I will write about strange phenomena that occurd to Pioneer 10 and 11 spacecrafts.


Pionner – artist’s concept

Both of these missions are quite old in the space exploration sense. One launched in the year 1972 and the other 1973. They were made to explore outer part of Solar System (meaning still quite close) and after that they of course just went on.. there is no way to retrieve object so far and it would not make much sense.

We lost contact with both but before that we knew how far they were because of their signal. There was something wrong about it anyway, every year when we predicted where they would be they would lack behind about 400 kilometers. Thats almost the length of Czech Republic though Pioneer 10 is able to cover the distance in 33 seconds so that is not much of a difference. But… there is a lot known about the forces acting on the spacecrafts and those could not be it. For example gravity from Sun is slowing them down but it is a thing that one can account for quite easily.

It took few decades to solve this problem (paper finally explaining it was published in 2012). Now we know that it was because of radiation from the spacecrafts as it was losing heat. Pioneers were spin stabilised so that their antennas always pointed towards Earth. The way it was build scientists found out that the radiation causes acceleration towards Sun. But it is kind of weak only: (8.74±1.33)×10−10 m/s2

Thats now much but in Viking program if radiation pressure from Sun (which is a different thing of course) would be ignored it would miss Mars by 15000 kilometers which is quite important.


Pionner picture: By NASA – http://nssdc.gsfc.nasa.gov/image/spacecraft/pioneer10-11.jpg, Public Domain, https://commons.wikimedia.org/w/index.php?curid=2878008

Europa Multiple-Flyby Mission

today I am going to write about proposed mission to investigate Europa.

Europa Multiple-Flyby Mission is a plan consisting of orbiter and a lander directed towards Jupiter‘s moon.

The reason why to choose Europa is quite clear. There is probably liquid water under its surface and if one launches such a thing, it might get public’s attention.[1] (Which might be now more important than ever considering how Trump wants to cut down NASA’s budget especially on the most important thing that they do: Earth’s climate monitoring.)

First of all the orbiter, which would be launched in the next decade, would learn as much as it could about the surface of the moon, Jupiter’s magnetosphere (see later), weird water

Composite image of Europa superimposed on Hubble data

This is two images of course. The original does not have the Europa in middle but only black spot. You can see the plumes on roughly 7 o’clock.

plumes and so on. There are 9 instruments together planned.

Instruments on those orbiters are able to collect data faster than we can receive it. This is because there are more mission that need attention of our receivers. Those are not some small receivers but specialized ones and all missions have some time to send information. For example New Horizons, just from its flyby of Pluto kept sending data for some 6 months.

In case of Jupiter oriented mission this might be a problem because Jupiter has extremely strong magnetosphere which will probably damage the instruments in matter of few weeks. This way it is best to get close to Europa and then get away as soon as possible and send the data later. This can not be done for the lander so it really lasts in matter of days. (Yes, it is still a problem even if you cover your equipment under 150 kilograms of titanium as is planned!)

The lander is thing planned even further into future, around 20 years or so. Much can change and we will see what the priorities are at that point.


[1]People will probably get quite excited by mission promising founding signs of extraterrestrial life.

How do we know that Sun is a star?

today I will shortly explain how is it that we know that Sun is a star and why it is not so trivial.

When you look up on the clear sky in night you see dots and they are said to be basically the same thing as our close Sun. They definitely shine, but not so much, they are not very warm, light up in different time than Sun, for some reason twinkle and are way smaller, even with binoculars they are still dots.

Hell yeah, they are quite small dots! Even if you take our best telescopes you will always have them so tiny! They are “point source of light”, which means that they are simply so small that from our view and practical purposes they are dimensionless.

They are huge though, most a bit smaller then Sun but still big, but so far away that they seem only as points. If even now we can not see the star’s surface as anything else than a dot, how do we know that it is the same thing as Sun?

The thought of Sun being star was there for some time. I found that already guys in ancient Greece thought that, the same idea came to the famous row of astronomers like Copernicus, Galileo, Kepler, Newton and others but they still did not have an access knowledge that would prove it.

In 1838 Friedrich Bessel measured the distance to star for a first time without considering anything about it (I guess he might have used stellar paralax but I am not sure). He found that the distance is huge, as we know today and soon we calculated that these dots are actually about as bright as Sun, also with astronomical spectroscopy scientists found out that what is happening there is also happening here. To make it clear, we do not have a “close up” image of any star, nor do we have image of any exoplanet.. for now that is simply impossible, still we can admire the cool Jupiter that Juno is taking pics of! (it is literally porn for eyes 😉 )


Polaris won’t be North Star forever

today I will write about precession and what effect it has on our sky.

Polaris is the North Star or Pole Star. This means that it is close to the celestial pole. Celestial pole is a point created by expanding the Earth’s axis of rotation and piercing through the celestial sphere which is imaginary “area” where stars sit. (For Earth based observations you do not really need to take into account that the stars are in completely different distances from us)

Precession is shown by the circle on the top.

But Polaris was not always the North star. For example when the Great Pyramid of Giza was build aobut 4600 years ago, there were two shafts from the tomb added. One points towards some random stop in the sky and the other one to Polaris.. oh wait but 2600 BC it pointed to Orion’s Belt and the star Thuban in the constallation of Draco. Orion was in Egyptian mythology connected to the god of dead Osiris and Thuban used to be the star closest to celestial pole. WHY?

Orange circle shows how the celestial pole’s position will change during the next years


Because of precession. That is an effect on Earth by Moon and Sun. The same way as gyroscope creates a kind of cone shape with it top, Earth also rotates like this but very slowly, it takes about 26000 years to rotate once. This type of precession is also called axial precession.

On the southern hemisphere the South Star is Sigma Octantis. It has very high magnitude so it is barely visible and not very good for naked eye observation. This will of course also change in the next hundreds of years.

Because of precession astronomers have to update every 50 years the positions of stars and objects, right now we are in what is called J2000 epoch and the next one will be J2050.


1st picture: By NASA, Mysid – Vectorized by Mysid in Inkscape after a NASA Earth Observatory image in Milutin Milankovitch Precession., Public Domain, https://commons.wikimedia.org/w/index.php?curid=3993432
2nd picture: By Tauʻolunga – self, 4 bit GIF, CC BY-SA 2.5, https://commons.wikimedia.org/w/index.php?curid=891838


Orbital period


in today’s short post I will write about orbital period of planets, more accurately synodic and sidereal period.

In the post about year and how difficult it is to determine how long it is, I mentioned that there are some ways you can measure the time it takes for planet to orbit star.

Sidereal period is the time it takes for Earth or other object, orbit once with respect to distant stars.

Now distant stars are great because they tend to be on the same spot most of the time. For example on the Voyager plague there is a map to show the position of distant pulsars, why? Because such things are stable, easy to see and far away. For year we use stars in Milky Way which is still fine, most move by fractions of arcseconds every year which is something you can not notice with eye and has some effects in thousands of years.

Sidereal period of Earth around the Sun is 365.25636 days. (I wonder if you could talk about something like sidereal period of Sun around the center of Galaxy, probably yes)

Synodic period is about two bodies orbiting Sun for example. It is the time that it takes for the two objects to get to same position. So if Mars and Earth are right behind each other (which is called opposition), synodic period is the time it takes for it to happen again. Now of course both planets orbit and the faster one (the one closer to Sun) always has to make at least one revolution. When that happens it just needs to catch up with the slower planet. With this simple thought you can come up with equation that lets you calculate the synodic period:


(lower case p is the sidereal period of the object with longer period)

Thats about it for know, enjoy your winter holiday while/if you still have it!