Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: neilep on 21/10/2008 11:37:26

Title: How Can We Know Which Star Is Nearer To Us ?
Post by: neilep on 21/10/2008 11:37:26

Dear Starologists,


I called into my local 'Stars-R-Us ' this morning and placed an order for this bunch of stars !

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Nice eh ?...being delivered next Tuesday.

The salesman (Hi, I'm Edgar I'll be your star-seller today) advised me that I should get them all vaccinated and micro chipped so that I could tell where they all are. Apparently they're a mischievous lot and often like to stray on various meandering trips ! So, I've made an appointment at the vet next week.

Some do wander very far though and although they look as if they are all the same distance away, some are in fact much farther away than others. To highlight this I have klevurly identified two stars that seem the same distance away, but one is indeed many times farther away than the other.


So, to enable me to find out how far my stars are what do I have to do ?...how does one tell the distance away that  stars are ?


Thanks

Hugs et les shmisheys



Neil
Star Owner
xxxxxxxxxxxxxxxxxxxxxxxxxxx

Title: How Can We Know Which Star Is Nearer To Us ?
Post by: lyner on 21/10/2008 12:08:49

You've heard of Parsecs (a space distance which is about 3 light years or  3.08568025 × 10¹⁶ m)?
As we move around in Earth's orbit, the near stars appear to move against the background of really distant stars. The effect is called parallax and you can see it as you move your head from side to side; distant objects in the room seem to move in relation to nearby objects.

The star motion is too slow to spot but two photos taken with a telescope will show subtle changes in the layout over a few months. A star for which the apparent motion against the background stars is one arc second (1/3600 of a degree) when the Earth has moved by one Astronomical Unit (the radius of the Earth's orbit) is said to be one Parsec (1Pc) away.

Astronomers used to flick between two pictures rapidly to see the difference. Nowadays you can do it with two computer images - the nearest stars move the most.
You need to check, though, or you may be looking at a planet or asteroid, which could give an odd result.
It's an excellent method for judging the distance of relatively nearby objects.
When you buy your telescope, you'll be able to do this.

Title: How Can We Know Which Star Is Nearer To Us ?
Post by: Evie on 21/10/2008 14:50:27

On a side note, you actually can "buy" a star! Well, I guess it's more like buying the name of a star, but if you name it after yourself, then you could say it belongs to you, right?

Here's a link for the International Star Registry. I named a star after my mom and gave her the certificate with its location on it for her birthday. A fine gift for the astronomy enthusiast in your life, in my opinion.

(This is not a solicitation for business and I have no affiliation with this website)   [;D] [;D] [;D]

http://www.starregistry.com/

Title: How Can We Know Which Star Is Nearer To Us ?
Post by: RD on 21/10/2008 16:01:49

By measuring the apparent brightness of certain types of star it is possible to calculate how far away they are.
This can only be done with "standard candles (http://en.wikipedia.org/wiki/Standard_candle)": stars whose actual (not apparent) brightness is known,
 e.g Cepheid variable stars (http://en.wikipedia.org/wiki/Cepheid_variable) whose absolute luminosity can be calculated from their frequency.

Title: How Can We Know Which Star Is Nearer To Us ?
Post by: syhprum on 21/10/2008 16:48:48

The third way which is more applicable to distant galaxies than individual stars is to note how much strong lines in their spectrum are shifted and apply Hubble's law.

http://en.wikipedia.org/wiki/Hubble_constant

Title: How Can We Know Which Star Is Nearer To Us ?
Post by: lyner on 21/10/2008 18:46:47

Quote from: syhprum on 21/10/2008 16:48:48

The third way which is more applicable to distant galaxies than individual stars is to note how much strong lines in their spectrum are shifted and apply Hubble's law.

http://en.wikipedia.org/wiki/Hubble_constant

Yes - and you could use Cephids too, but I think the question is originating from a recent or would-be personal telescope owner.

Title: How Can We Know Which Star Is Nearer To Us ?
Post by: Karen W. on 22/10/2008 06:43:02

I don't know how to tell the distance....but I must say I love the stars and sometimes its so clear here like tonight where it looks as if I could reach out and pick one right out of the sky.......... very beautiful and close... even if its just my imaginagion....

Title: How Can We Know Which Star Is Nearer To Us ?
Post by: Don_1 on 22/10/2008 15:09:00

I have an extremely long tape measure which you are free to borrow on Thursday afternoon if you wish, but I must have it back by 4 pm as I intend to find the answer to the age old question 'How long is a piece of string?'.

Title: How Can We Know Which Star Is Nearer To Us ?
Post by: Soul Surfer on 27/10/2008 18:35:18

Most stars on the whole are very simple things and fit on to diagram called the Hertsprung Russel (HR) diagram whigh charts the colour and detail in their spectra with the brightness of the star. The actual distance of many stars was measured using parallax and a satellite called hipparcos many years ago.  laso the relative brightness of stars has been nmade using observations of star clusters (which are all at a similar distance.  So once you know how bright a star is and where it fits in the HR diagram you know its absolute brightness and therfore you can calculate how far it is away.