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 😉 )


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!


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 😉


Solar sails

have you ever wanted to be space pirate? To just fly through Universe close to speed of light and sometimes stop on some planet to steel some stuff? Well now, your space craft can even look like a ship, with huge sail!

Solar sails are sails like any ordinary sails. They even use wind, wind made of photons!

On the picture above, you can see IKAROS spaceprobe, the first succesful probe to use solar sails.

Those solar sails are powered by nothing more than the electromagnetic radiation coming from the Sun. It then pushes the probe because of photon’s momentum[1].

But photon has no momentum!

Yes according to Newton’s mechanics it should not have a momentum because it has no mass.


p is momentum, m is mass and v is velocity (speed).
If you would use this you would get that photon does not move and it does not have momentum but if you use theory of relativity as I already showed in the post about conservation laws you will get some real value, using what is called “relativistic mass” which is not zero for photon.

The IKAROS’s sail was 20 meters on diagonal and most of it was 7.5 µm thick so it was very light.

Whole probe had 315 kg while the sails had only 2 kg. This is about average mass for probes since New Horizons had about 450 kg while Jason-3 about 250 kg.

The pressure of the solar wind from Sun was 1.12 milli newton and it was able to gain velocity of even 400 m/s or 1440 km/h.

This method is not much useful for fast speedup and also for deep space travel since the radiation decreases with squared distance, but still you can be a local pirate.



[1] The photon’s momentum is transfered to the solar sail and because of conservation of momentum the sail must be pushed a little bit while the photon bounces away, this is the same effect as with a shooting rifle. When you shoot the bullet goes forward while the rifle backwards with the same momentum.

2nd picture
1st picture


The Universe is enormous

I was thinking what topic should I mention today and remembered that the Universe is huge, and it is so huge that we completely underestimate it (at least I think that I still do).

First I will turn towards our planet, the Earth.
Here the biggest misconception is the size of Africa, you see the problem is that in most maps of Earth which you will see is Africa in the middle. If you know little about geography you know that there is no way to perfectly put our planet to scale on map. There are some ways which will be more accurate than other but most of the time Africa is going to be smaller than other continents. continent_infographic-01 copy

OK, now compare this map above with the scale on your home atlas, Africa is going to look tiny probably with Greenland, Siberia and Canada huge.

Now look at the picture of Earth and Moon distance, they are so little, Earth would be able to fit there so many times!

Now, seriously, look at this amazing page: THIS You start with Moon which is wide as one pixel. Next you will see Sun which seems to be pretty huge. Now if you click the speed of light button you will start to move slowly to right. Oh my god, the speed is so awfully low!

On top of page you have the bar with planets so you can click on them and ride from one another, remember, it is TO scale, and after you drive through whole map they say: You would have to travel 6,500 more maps like this to get to something.

This is huge, we are from Sun only 150,000,000 km.

OK´, Sun is small, lets see why:
1st picture shows that Sun is big:

2nd picture, well Sun gets little smaller:

3rd picture is actually a whole different story:
Now here is the last to compare it all, with little bonus of Canis Majori:
Ok but all of this stuff is so freaking small compared to whole Milky way! The radio signal from Earth which traveled for tens of years is not even visible on map of Milky way!
You can fit Sun 1420 times next to each other inside VY Canis Majoris.
And  you can fit Earth like this 109 times.
This means that you can fit Earth 157,780 times inside VY.
The diameter of Milky way is roughly 140,000 light years. Where one light year is 9,460,730,472,580,800 meters.

This is 741,669,055,548 Earths for diameter of Milky way. 2,540,000 light years is the distance to Andromeda galaxy, the closest galaxy.

Virgo Supercluster has 110,000,000 light years. Easy. On the next picture from @HighTechPanda , you can see the comparison of largest galaxy to Milky way, enjoy!And last, observable universe has 93,000,000,000 light years in diameter.

Still so underrated.


Africa picture


Leap seconds

I was just reading post by Science Geek and then I realized that I was learning some stuff for school on similar topic so I decided to make a short post about it.
Today I will write about leap seconds.

Look at the picture on the left. Now look at it again if you did not find the strange thing there. Unless you have some kind of strange clock you should not see 60 seconds normally but you should see instead one more minute and 00 seconds.

So lets take a look on what exactly happened here.

So this picture is picture of time when leap second was added to our time because our day was shifting with actual solar day which corresponds to our position with Sun (this gets messier when you see that on this also our orbit and axis have effect).

The problem here is that the rotation of Earth for longer term is unpredictable, of course we are talking about very small amount of time. The thing is that lot of stuff can change the Earth`s rotation: earthquakes, crust moving relatively to core, slowing of the rotation because of friction from tides (about 2ms per century) and many others, actually anything that happens here is slowing Earth rotation down.

There are of course two types of leap seconds but only positive ones were added for now, actually 26 of them and last one on June 30, 2015. This makes some problems in computing because of course all-time running programs with lot of data are not very well prepared to just add one second. This is also why those seconds are always allowed to be inserted two times per year.

On the graph you can see how the time changes (y-axis) through years (x-axis). Those fastest vertical changes are leap seconds. As you can find on Wikipedia on the table with leap seconds, around the year 2006 there were none needed.


Both pictures are from wiki article about leap seconds

Optics: 1) Reflection

here it comes, here it goes. I realized that if I want to really know something about astronomy I have to use physics. For now my first goal is to learn something about optics and particularly about binoculars and how they work and what is the math involved! Today I will write about very basics and it is reflection of light. Probably I will add something to it on my YouTube channel with some examples and I bet it will be fun!

When we are talking about optics and stuff around we assume that light or electromagnetic radiation behaves as particle (on the level where I am), the thing is that as rest of the really small particles like quarks and electrons and neutrinos, light behaves both as particle and wave which called wave-particle duality. This is very interesting but let it be for now.

As you see on the first picture from wikipedia article reflection, there is laser pointed on mirror which as you can see is reflected to the right.
This is important, the light gets reflected from mirror because photons bounce in the same angle from which the came.
On the right you can see the ray of light starting at P, reflecting from O and flying to Q. Both of the angles are are same from imaginative line that has 90° angle with the mirror. θr=θi  … r stands for reflected and i stands for incident. This also means that the angle of the ray and the mirror equals to the one on the other side. This is for mirror but of course other things are reflecting light too but because their surface is not smooth photons are flying all around and you want get the exact image of the thing that was emitting/reflecting the light first even if it is not absorbing any spectrum like snow. This is also the reason why it is dangerous to not wear anything across your eyes when you are a long time on place where is snow because over time all of this light can blind you.

This can happen in matter of couple of seconds if you look directly into Sun since the inside of the eye can be sun-burned in similar way like your skin and the damage may be permanent so watch out!


Stellar classification

what you can see on the picture is extremely cool (hot actually) even that you don´t know it yet. It is called Hertzsprung-Russell diagram and I will try to explain it with the rest of Stellar classification.

So there is first thing I have to clear out: What is Absolute magnitude?
Absolute magnitude describes how bright is star. This of course depends on the distance from which you are looking. It is called absolute because of fixed distance of 10 parsecs (around 32.6 light years). There exists also apparent magnitude which is taken from Earth´s view.

This absolute/apparent magnitude is in logarithmic scale. This means that for every point in magnitude, brightness increases by x2.512. So for 5 points, brightness increases 100 times (2.512^5=100.0226), this corresponds to what was created in ancient Greece. Also it is important to note that negative means more bright.

Absolute magnitude is Y-axis on HR diagram (it can also be luminosity) while X-axis is spectral class or sometimes surface temperature.
Spectral class corresponds with surface temperature, mass, solar radius and its rareness.
There are usually seven types but on the picture you can see nine.
Those seven are OBAFGKM. Where O type is hottest and M coolest with lowest mass.
You can use mnemonic to remember it: Oh Be A Fine Girl (Guy) Kiss Me (I really like this one :D).

And the last thing you need to know about the diagram are those roman numbers. Those are luminosity classes.
VII: those are white dwarfs.
VI: subdwarfs
V: main sequence stars
IV: subgiants
III: giants
II: bright giants
Ib: less luminous giants
Ia: luminous super giants
0: hyper giants! (those are shown on the right picture, blue line is orbit on Neptune and those stars are: blue hyper giant, yellow hg., red super giant and red hyper giant)

So now we can take our Sun and find out what we can tell about it.
Wikipedia says that spectral classification of Sun is G2V.
G: it is spectral class (girl/guy)
on the diagram it is rather on the left and you can see it is yellow.
2: means that Sun is in the upper part of G spectral class, this is only for subdividing those classes where 0 is highest and 9 lowest.
V: (it is 5) this means that Sun belongs to main sequence stars.

Now you can easily find where it stands.
Another example could be 10 Lacertae a star in the constellation of Lacertae.
O9V is its classification.
O: (Oh) you can see it is a super giant but with “only” 9 so it is rather smaller and cooler super giant.
V: again this one is lying in the main sequence so it would belong to upper left corner of diagram.

That´s about it, if you ever check for any star, this classification can be extremely helpful for you.


Note that there is table for spectral classes (taken from wikipedia page stellar classification):

O ≥ 30,000 K blue blue ≥ 16 M ≥ 6.6 R ≥ 30,000 L Weak ~0.00003%
B 10,000–30,000 K blue white deep blue white 2.1–16 M 1.8–6.6 R 25–30,000 L Medium 0.13%
A 7,500–10,000 K white blue white 1.4–2.1 M 1.4–1.8 R 5–25 L Strong 0.6%
F 6,000–7,500 K yellow white white 1.04–1.4 M 1.15–1.4 R 1.5–5 L Medium 3%
G 5,200–6,000 K yellow yellowish white 0.8–1.04 M 0.96–1.15 R 0.6–1.5 L Weak 7.6%
K 3,700–5,200 K orange pale yellow orange 0.45–0.8 M 0.7–0.96 R 0.08–0.6 L Very weak 12.1%
M 2,400–3,700 K red light orange red 0.08–0.45 M ≤ 0.7 R ≤ 0.08 L Very weak 76.45%

Stars of our Solar System: Sun

after few hours of study I am bringing next post, this time I am returning to where everything begun, The Sun!
So Sun is the center of our Solar System. But it is far away from the center of our galaxy as you can see on picture (it is about 27000 light years).

Sun is the brightest object on our sky with apparent magnitude -26,74 (I will definitely make post about apparent magnitude because I found it very interesting). Sun makes up of 99.8% of Solar
System´s mass so you have no way of Moon Photobombs the Sunthinking that Jupiter is big. It is 1.4 million kilometers across with mass 333,000 of Earths.

The surface temperature is 5,000°C. Surface here is the edge of what we see, or also edge of photo sphere which I will mention later on.
In the core there are temperatures about 15,000,000°C.
Sun is fusing hydrogen into helium as most stars do. Still in the core there are some more heavy elements like carbon, oxide, neon and others but only in small parts.

Every second our Sun burns 700,000,000 tuns of hydrogen which fuses into 695,000,000 tuns of helium. Those 5 millions is heat escaping the star. This is the same weight as 15 Empire State Buildings! But even more astounding is that this energy equals to 400 billions of megatons of nuclear bombs every second! That is why we feel the heat even from such a distance.

So, there are few layers. (Whole Sun is rotating but different layers in different speeds.)

Core: is the hottest part which takes up over 20% of Sun´s radius (not 20% of volume, remember, it is sphere). Here the fusion takes part.

Radiative zone: stretches to 0.7 of Sun´s radius. There are hypothesis that this zone with next zone creates magnetic field of Sun. Also here the energy is transferred by diffusion.

Convective zone: This zone is almost the rest of Sun´s volume. Here like in ocean hot gas goes up and colder down in process called convection.

Photo sphere: is the visible part of Sun. It is thousands of kilometers thick and much much colder and it has very low density (0.37% of air density on sea level).

Corona: is the outer layer of Sun. We are not really sure why but it is ridiculously hot, about 1-2 million °C even that it spreads 1-2 Sun radii from Sun´s surface. It is even less dense than photo sphere so you can not see it without telescopes blocking Sun or Sun eclipse.

For photon it can take 100-200 thousands year to escape from core because right after photon is created it collides with some particle which blasts it away with less energy so this photon is kinda lost for a long time.

Solar flares are events when charged stuff interacts with plasma. This creates eruption (last picture).
Coronal mass ejections happen when two opposite magnetic fields interact with each other throwing lot of stuff into space and some electromagnetic radiation (first picture).

Both events are connected and can occur together. In the year of 2012 we were very lucky since one coronal mass ejection appeared but thankfully missed us (this CME was so strong that it would probably cut off most of electronic circuits and we would be recovering for very long time).

This is end for today, I hope u guys liked this little bit longer post.

PS: I was taking information from lot of sites but I forgot to copy their URL but it was wiki, NASA and some others from first pages on google.

For more about stars, visit one of my old posts about life cycle of those balls!
And to see what kind of dwarf Sun is visit this post!

Planets of our Solar System: Jupiter

lets see what we got here, the biggest planet of our Solar System into which all other planets would fit with space to spare. It is Jupiter, named after Roman god of gods orJupiter.jpg Zeus in Greece mythology.

It is nine times wider than Earth but its mass is 1300 times larger. It is the fastest spinning planet, one day on Jupiter is 10 hours long which makes him 6% less like a circle. Mean distance from Sun is 800,000,000 km or 5.2 AU.

Jupiter is the closest gas giant, which means that he has no surface only thicker and thicker poisonous clouds with various gases. Darker parts are called zones and lighter belts, both of them are rotating in opposite directions. This process is powered by the internal heat of planet (Jupiter loses heat more than he receives) and by fast rotation.
On the picture you can see The Great Red Spot, it is on left of southern hemisphere. That is storm which lasts for decades but now we know that it is shrinking and eventually it will disappear. But for now it is stronger than any storms we ever hope to have on Earth with winds of over 500 km.

When we would dive beneath its deadly atmosphere we would appear in ocean of metallic hydrogen (hydrogen atoms that are sharing their electrons which makes them act as metal). Underneath we are not really sure but there can be solid core of metals and/or rocks.

While Jupiter is really large it is not even close to becoming star, it would have to be 12 times more massive. There exists a theory that Jupiter helps Earth by changing the pathway of comets and other stuff in space but on the other hand it could work in the same opposite way, but still we are not dead yet.

Juno (Hera) spacecraft is right now heading towards Jupiter. In the half of 2016 it will arrive and for 15 months it will collect the most accurate data that we ever had because of its close orbit.

For now there is 65 known moons orbiting Jupiter and I will definitely mention some of them in the future.


PS: be sure to check out Mercury, Venus and Mars!