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,
2nd picture: By TauÊ»olunga – self, 4 bit GIF, CC BY-SA 2.5,


Space NEWS #10 (Very close exoplanet)

today I am bringing news about the closest ever found exoplanet that is also potentially habitable. This planet is orbiting Proxima Centauri, the closest star to Sun.

This is great news. Like really, what is the probability of finding one of the best candidates for Earth like planet closest to us that it could get. But to be clear of what is really going on, it is not as that we are going to get a picture of it. Not at all, we do not even know its size (is probably above 1.3 of Earth’s) or anything about its composition. Its just that it is very very likely that the planet is there because of Doppler shifts and other fancy astronomical tools that enable scientists to discover exoplanets.

No, this is not how the planet looks like.. but yay! Random artistic pictures!

Proxima is red dwarf. This means that it is smaller and cooler than Sun. The difference is so huge that the planet may be in habitable zone even though it is probably only 7.3 million kilometers away compared to Earth’s 150 [1]. So if there is water it may be liquid but nothing is very sure. If there are some greenhouse gases it is probably warm enough.

Before leaving, just check out this cool comparison of the angular diameter (size) of Sun and Proxima from Earth and from the new planet (Proxima b):

Sun and Proxima compared

Yes, any life on Proxima b would have much bigger and redder star to look on.


Check out these two pages for more info: 1) 2)

[1]Proxima has surface temperature of 3050K, 0.1 percent of SOlar luminosity, radius 0.14 and 12% of Sun’s mass.

Where do equinox come from?

today I was trying hard to understand basics behind the coordinates that are used for stars and other celestial objects, once you grasp some basics you will get it, important part is the equinox and the “mechanics” that are behind it.

The celestial sphere with all stars at one distance

Basicly what you see on the left gif is the celestial sphere around the Earth (most of these things are geocentric since it is easier). Red line is the ecliptic. This is basicly the line that Sun follows over year, of course such motion is purely apparent but it is important to remember this one.

The white-green lines are the lines of equatorial coordinate system. The middle should be Earth’s equator though it does not match it much.

There are two points in which ecliptic and equator intersect. These points are called spring

How ecliptic is made (not to scale)

equinox and autumn equinox. When Sun passes through them the day is everywhere on whole Earth the same as the night. You already know that this happens happens twice a year, once for each equinox.

I will get to the coordinates in another post, hope you enjoyed this one 😉


Where is the edge of Solar System?

today I want to look on the problem of edge of Solar System. The problem is that such a border is not very clear. It is similar problem as the classification of what is planet and what is not, simply because there is no clear distinction in size or so for something to be planet. Biologists also had/have this problem with defining what is life since they discovered that there are lot of small things that are lying on the edge of dead (it was never alive) and alive.

So whole post I will be working with this picture, so take time to acknowledge what is there:

Voyager 1 entering heliosheath region.jpg

Sun is in the center.

So the short answer is that heliosphere is the edge of Solar System. It is defined as region with the border where Sun’s solar wind is stopped by the pressure of interestellar medium.

Solar wind is the flow of plasma from the Sun. It is pretty fast, up to 400 km/s or even more. This plasma is then hitting the interstellar medium which is stuff from other stars and simply dust and so on.

Since this solar wind pushes the stuff out we have smaller pressure inside our bubble. This creates the border called heliopause where solar wind is slowed to 0 velocity.

It is best to define the region like this because otherwise Sun is technically visible anywhere in the space and its gravity also just decreases a little bit by the distance but solar wind just stops.

You may have noticed that I did not mention the termination shock which is another border in Solar System (btw. heliosheath is just the region between heliopause and termination shock).

It is the border where the velocity of the solar wind decreases below the speed of sound in space [1]. This creates a termination shock which I will explain in other post when I will talk about the speed of sound!


PS: also I promised something about orbitals so I should do that too..
PPS: Bow shock probably does not exist and it should be shock wave of interstellar medium.

[1] Oh yes, there is speed of sound space too. It varies from region to region but since there is dust and other stuff lying around the speed of sound is roughly 100 km/s.

How to! 4) Go stargazing for the first time

since I went out stargazing couple of times already, I would like to mention few things here for you, when you decide to go alone or maybe with your boyfriend/girlfriend stargazing. While I live on northern hemisphere all of these tips will be useful to south people.


Check out the time when the sun sets where you live. This page is quite useful for that, you just need to insert your location.

It is quite useful to know what these terms mean, astronomical dusk is what you are looking for.

So you need to watch out for the time when first stars/planets appear which will be some time after the dusk, of course there must be clear sky which you need to check on Google forecast [1] or in TV.

Then while it depends on the time of year, it is good to take some extra clothes, because most probably you will be standing still for some time, so you might get cold.

How to stargaze

First option: take some sky map on paper with you. You can print some from internet but check if you are printing the right hemisphere. For this, you will need also some light, but not white, since you would never build night vision, take red, eyes are not so sensitive to it.

Second option: take your smartphone and download application with stars, I use Star Walk 2 Free and it is pretty good, especially because there is option for night vision so it is red, this is very useful though you must never lock your phone, because when you want to use it again the light from you display would pretty much destroy the night vision you build up.

What is night vision anyway? It is the activation of all your non color sensors in eyes and the adjusting of your vision in darkness by enlarging the part that collects light, it take about 30 minutes though you may see the effect even after 4 or 5.

Pick a good location

Be sure to pick a good location. If you are in big city, than make sure to drive to countryside because the light pollution would just waste your time.

Best is hill though it is good to be on some field or place where there are no trees.

Keep away from any buildings and streets. It is important for you to keep the night vision, one single mistake when you look in street light could destroy the whole process.

Enjoy 😉


PS: it is better to go stargazing when there is new moon, otherwise, full moon spoils the view of huge part of sky.

[1] To get in Google forecast just type “weather” and “your location”.

Altair, Award, Dreams!

For last (edit: first 😀 ) I decided to create second blog, do not worry it will never ever step into way of this one which is main and means a lot to me.

What is it about? It is about dreams, more accurately, lucid dreams which are dreams I want to learn to dream. Are you confused? Well then you will have to check out the blog and follow it too 😉 !

The posts there will be sometimes frequent sometimes not but I will continue to post every other day here, as I promised.

Make sure to check it out!

Today I was doing some work in school with different Wikipedia pages. I picked Altair which is pretty interesting star so I wanted to share with you what I found out.

Altair is 12th brightest star and it is located in constellation of Aquila.


The area of constellation of Aquila in the sky.

It is one of the closest balls of plasma around, 16 light years. Its spectral type is A and it is brighter and bigger than Sun. What is als interesting is that it rotates quickly, one turn in 9 hours compared to 25 days for Sun. This is important for its shape since as it rotates the shape of the star changes to ellipsoid or “stepped on” ball. This has very interesting effect, the poles are brighter because of gravity darkening. The surface gravity at poles is greater making them brighter.

I have got award again, and again Versatile award which I had about week back or so.

I was nominated by mliae, thanks a lot. I would be happy to fill it but I nominated my most favorite blogs in recent awards already and I would not want to spam them again so for now I will just keep it for myself (do not take it as that I do not appreciate it, I do). 🙂





Telescope of new generation

today I would like to mention new kind of telescope which is right now being build. It is quite amazing piece of human technology, The James Webb Sp Telescope.

Named after James E. Webb who was leading NASA about 50 years back. First they wanted this telescope to name Next Generation Space Telescope but then they decided to give James Webb the honor.

Labeled Spacecraft

Above you can see how it should look like when we will launch it. It is telescope which should work instead of Hubble’s Space Telescope which even that it did great work, is not good enough right now. James Webb Space Telescope should have even better view in the vastness of Universe. Also more details which means that for example, we could get much more information about exoplanets, we could even start to analyze more of their atmosphere and learn more about stars and so on.

Still Hubble’s telescope has some time since James will be launched in 2018 in French Guiana. Here you can browse some pictures for sun shield testing, this is the part that is turned towards Sun and protects all the fragile tools that are on the telescope because in space, radiation could easily destroy transistors and other equipment.

The most kind of shocking part, which you can see above is the primary mirror. You can see that James Webb has upgraded a lot from Hubble. This mirror is actually too big so it had to be made from separate pieces, hexagons. It was quite fun to watch as they for months placed those plates on the structure. The mirror is made from beryllium because it is strong and light element and the top is covered in gold for protection from radiation. This kind of mirror is used on optical telescope and the bigger the mirror is the better the image which is formed. This is why they must be so polished, it is also important to have the working area clean so this is how the engineers usually look like:

JWST Team Photo with Completed Flight Instrument moduleThere are few more instruments that collect the light in various spectrums. For now we must wait before they finish whole work, and there is nothing more to do than admire the work that Hubble has done for us (and is still doing (actually the work of engineers and scientists)).


Pictures from here here and here.

What is the color of Universe?

today I want to write about the average color of the Universe.

The average color of the Universe is not black. I mean, when you look at the sky in night it seems that there is black everywhere, but that is actually no color. When we speak about color we say that something is red, that means that it reflects red light.

Right, light, but when there is nothing shining it does not have any color because it can not reflect anything.

The average color of the Universe was found in 2002, year before the same team discovered the color which you can see below but it was corrected several months later because there was mistake in the software.

So how do you find such a color? Well you take the color we see of various galaxies and stars and so on and make the average of all the photons wavelengths creating the color which you can see below:

This color gets redder over time as there are more red stars in the Universe. In RGB this color is: 255,248,231.

Meet the color of the Universe, Cosmic Latte.


Those two color were taken from here.

PS: Next week there wont be practicly any posts since I will be away learning some math.


Multiple star systems

Source: Wikipedia page Center of mass

Source: Wikipedia page Center of mass

today I will write about binary and multiple star systems. Those are systems where two or more stars are orbiting each other and sharing THE common center of mass.

Center of mass is exactly what it says. Center of mass of course can apply not only to stars but to humans, to planets and actually anything that has some mass.
On the picture you can see the estimated center of mass after gymnast performs cartwheel. (It is estimated because our body is so complicated that it is not easy to count where exactly it is.)

So this center of mass is a point in space towards which all the stuff is kinda turned.. so if you have a binary star system as is on the gif you can see that the smaller star moved the center of mass little bit towards itself and you can not actually say that the star orbits the larger one but both are orbiting the common center of mass or also the barycenter. Alpha, Beta and Proxima Centauri.jpg

For example Alpha, Beta and Proxima Centauri (circled) are trinary system. Or also Pluto and Charon are binary planet system.

So you can have binary system of two stars but also one of them can be neutron star, or even black hole.

Those multiple star systems are very common actually 1/3 of all stars are in multiple star systems. It does not end of course on binary or trinary systems but there are even septuple star systems like AR Cassiopeiae.

It is very difficult to calculate their barycenter so there is method with which you can simplify whole process a little bit. If there is more than two stars in the system you can make a hierarchy of all of them.

a) is not simplified at all
b) is clear binary system (nothing to simplify really)
c) is trinary system. Two closer stars were taken and their barycenter was calculated and then as if it was one star it was compared to the other star to create the final center of mass
d) is quadruple system where two barycenters each of two stars were combined
e,f) is now probably clear

In those systems planets can exist but their orbits have to be either small or huge compared to orbits of stars because otherwise they would be thrown out of the system. They can orbit only one or both stars.

One last thing. There are few ways by which we can detect them because usually we are File:Artist’s impression of eclipsing binary.oggnot able to distinquish star system and they look like one star to us.
First method is by eclipsing of one star behind the other. When one star crosses behind the other we can see the short dimness, this is similar to the method of finding exoplanets.

Astrometric binaries are binaries where one star seems to orbit around empty space which is usually neutron star, black hole or something which is not very bright.

Then sometimes when those stars are really close to each other one can transfer mass to the other one which can create accretion disk which we can observe.

Here are some other examples of binary star systems:


All of the pictures were taken from wikipedia pages Binary star, Star system, Center of mass and Alpha Centauri page as for information it was also taken from various wiki pages and also NASA (binary stars.)