spectral class

Altair, Award, Dreams!

Hi,
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.

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). 🙂

 

Dragallur

 

 

Standard candle

Hi,
have you ever wondered how do scientists measure distances far away in space? Maybe you have heard about supernova which was found about 11 billions of light years away. The problem is that when something is far away you don`t actually know if what you see is bright or close or dim or far away or the combination of both.

So here comes the standard candle. The standard candle is object in Universe which has always about the same luminosity.
The example of thing that is not standard candle is for example any star since when you are looking at it you don`t know its luminosity since it could be in spectral class O or K  and it could be next to you or far away.

Standard candles are supernovas of type Ia which are the brightest of all supernovas.
First of all I will try to explain what this supernova type Ia is.

This type of supernova is explosion of white dwarf which exceeds the mass of 1.4 the mass of Sun.

How this happens? This white dwarf has to be in binary star system so he can feed on his companion`s gases and get the mass again to trigger fusion. When white dwarf exceeds the Chandrasekhar limit which is 1.4 of Sun`s mass as mentioned above then it explodes in violent explosion called supernova Ia.
Actually it is not so simple because the supernova explodes in what is called “double detonation” which is caused by first explosion happening even before Chandrasekhar limit because of the hydrogen which is fused on the surface on helium (I am going to find out more about this on astronomy stack exchange so I will update it.)

Then the second and main explosion is triggered and the donor, the first star is thrown away from the system by the energy released (1-2*10^44 J).

So the important thing is that supernova works as standard candle because it will be always about the same brightness which is very important because than astronomers can calculate how far away it is because they know how bright this thing is.
Supenovas are used for distances greater than 1,000,000 light years because closer there is not enough of them.

Dragallur

Picture source

 

Stellar classification

Hi,
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.

Dragallur

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%