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Distance of stars

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Nov12-03, 09:02 AM
P: 10
please can somebody help me with this parallax equation:

D=distance to star
using the rule D=(d/2)/tan(theta/2)
when d = 300*10tothe6
and theta = 5*10tothe-5

what is the distance to the star in km and light years?
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Nov12-03, 09:19 AM
P: 27
Okay - assuming that you've given the units in kilometres and degrees...

To get the answers in km you should just be able to plug the numbers into a calculator.

To get the answer in light years you have to first calculate how far a light year is (in km, obviously).

Rather than me just giving you the answer, why don't you have a go, then we can see if our answers agree...

Nov12-03, 09:32 AM
P: 10
hi there thankyou for your interest in my posting jess

d is in km
theta is in degrees

Nov12-03, 09:36 AM
P: 27
Distance of stars

You'll be wanting to hit 'post reply' rather than 'new thread', then

Oooh look - we've been moved

Tom Mattson
Nov12-03, 09:41 AM
Sci Advisor
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P: 5,532
Originally posted by Jess
You'll be wanting to hit 'post reply' rather than 'new thread', then

Presto! The threads are merged.
Nov12-03, 10:53 AM
P: 10
for this answer i get a result of:


So, is this answer the number of km?

what is this answer in exponential form? ie: 34 * 10tothepower13?

1 light year is 9.467*10tothepower12, so in light years i think the distance will be:
27 light years

Please let me know if i am right
Nov12-03, 11:14 AM
P: 27
Yes, that's the answer in kilometres, and it's the same one that I've got.

34 x 10^13 km is correct as well.

If you take the speed of light to be 300,000 km/s, then a light year is 9.461 x 10^12 km - which looks roughly like what you put.

I get an answer of 36.3 l.y though - you might have typed a digit wrong somewhere, perhaps. Even a back-of-the-envelope type calculation gives an answer of at least 34, if you look closely.

Nov12-03, 11:17 AM
P: 10
thankyou very much jess!
I need the help for some uni coursework.
p.s. I am from edinburgh too!
Nov12-03, 11:20 AM
P: 27
This isn't Astronomy 1Ah or 1Ch work, is it?
Nov12-03, 11:28 AM
P: 10
i study at the university of abertay dundee and travel from edinburgh.
My coursework is from "horizons of science 1".
this module is concerned with the big bang, black holes, telecommunications and cosmological phenomena
Nov12-03, 11:32 AM
P: 27
Hehe - for a moment there I thought you might be one of my tutees (if that's the right word)

Good luck with the rest of your course...


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