Pareidolia

Hi,
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.

Dragallur

[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

Hi,
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:

https://qph.ec.quoracdn.net/main-qimg-0be932f563bde21614fc7bfbcff409d9


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]

Dragallur

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

Hi,
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.

Dragallur

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

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

Pioneer10-11.jpg

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.

Dragallur

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

Hi,
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.

Dragallur

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

How do we know that Sun is a star?

Hi,
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 😉 )

Dragallur

Polaris won’t be North Star forever

Hi,
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.

Dragallur

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

Hi,

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:

1/S=1/P-1/p

(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!

Dragallur

Sunset elevator

Hi,
today I will write about one particular physics problem that I was solving during weekend. It was pretty hard, but quite interesting set-up. (It is originally from Czech physics seminar called Fykos)


You and your boyfriend/girlfriend are sitting on a beach watching sunset. Luckily you are prepared to extend the romantic moment with elevator that will drive upwards. How fast does it need to drive for you two to be able to watch sunset continously?

Normally sunset related problems are about plane or car driving and how fast does it need to be for you to watch sunset all the time. That is freakin’ easy because you just need to drive at the speed that the Earth turns in your place. For Prague this is roughly 300m/s which is about the speed of sound.

This problem is way more unique. I do not know if my solution is correct since the people from seminar did not release solutions yet.

Basically you are standing on top of circle that is rotating at 300 m/s or also 0.00417°/s. You are soon leaving place from which you could see the sunset so you need to go up. The problem is that you are not actually going directly upwards to this place but as Earth turns your elevator rises in a line perpendicular to tangent of Earth at your paricular location, check out this desmos graph which helped me a lot to understand it (my creation): https://www.desmos.com/calculator/oftnm48s3b

Here is a picture though it is better to go on the original link which is very interactive:

(Check out complete end of post for explanation of picture) What does it mean for you in practice? In one hour you will be going almost 100 m/s. After 6 hours you will certainly be dead because the acceleration will kill you. At this point Earth would still be bigger on the sky though you would already be 500,000 kilometers away. After another three minutes from what I have considered last time you would be almost 3 million kilometers away and Sun and Earth would be the same size, at this point you would also ride in 1/3 of speed of light. But this journey still continues. After another 13 seconds you would go faster than the speed of light with acceleration of 14 km/s. There is not much time left but lets see.. 10 million kilometers would be reached by next 9 seconds. 5 seconds later you would go in freakin 10 million kilometers per second if it would be possible. One second before the journey would end you would reach 0.5 of AU. Soon after you would divide by zero which is dangerous[1]. After exactly 21600 seconds which is 1 quarter of day your elevator is perpendicular to this horizon, which sucks.

I bet your girlfriend/boyfriend would not be so happy about this trip though the first few hours would be amazing.

Dragallur

Explanation: black circle is Earth. Green line is elevator that with you turns left, after 21600 it will go 90 degrees. Red dot is the spot where you need to be in order to see sunset. Blue line is the original horizon.

[1]Do not be discouraged by only 0.5 AU. In the next mili and microseconds you would whizz through whole Milky Way and Observable universe as you would reach infinite speed.

How long is a year actually?

Hi,
today I will write about a year. The thing is that as in many other subjects when you look down into the simplest things you might find that they are not as simple as they seem. So how long is year? 365 days? 366 days?


You very well know that every 4 years we have 1 extra day in February. You might also know that this is because year is not 365 days long exactly but roughly 365.25 .. its important to say roughly because it is not perfectly true and it matters how you define one year.

First lets see how we define one day. One would say that it is the time that it takes for Earth to rotate once. Problem is that we need to define some object to compare it to, some ground, some reference point. It might be the Sun, but Sun is too close and since we go around it, this would change the length of the day.

Sidereal day is the day that is defined as a rotation of Earth around its axis compared to very distant stars that are relatively stable. 23.9344699 hours… that is pretty close to 24 that we use, but it is not what we use.

The thing is that we decided to use what is called solar day, which is in fact compared to Sun. As Earth rotates around its axis, it also rotates around Sun, which makes the solar day different length.

This is how the effect looks like. You need to turn Earth n.2 by little bit more since it moved around the Sun too.

Problem is that the length of solar day changes since our orbit is sligthly elliptical and when we are closer to Sun we are faster which means that the solar day is shorter and there is more time needed for the same spot to face Sun again. This effect adds up to almost 365.25 solar days in a year. If it was so simple we could just add one leap day every 4 years to make up this 0.25 difference but it is actually 0.242181 which makes difference over time.

 

Julian calender ran with 0.25 for a long time but after about 1500 years it was already 10 days behind of the real date and Christians wanted to predict Easter exactly so they changed on Gregorian calendar. This calendar is the same, except that if the year is divisible by 100 it wont be a leap year, though if it is also divisible by 400 it will be a leap year. This almost fixes the problem, though every 3216 years one day is still off from the real time. Yup. Check out this video to see how we can improve this slight mistake:

https://www.youtube.com/watch?v=qkt_wmRKYNQ

So thats it. But you can not really capture the length of year or day since it changes all the time (effect of other planets and what happens on Earth). Check out this video which I used mostly as a source, it has got cool animations that will help you understand it:

Dragallur