How do we determine the distance?

Hello.I hope my query qualifies as a quick question, but if not, no worries. My question deals with determining the distance and age of light being emitted from other stars or galaxies.I think (hope) I understand the basics of the Doppler effect, and how we discern whether a galaxy is moving away from or toward our galaxy, i.e. the red shift and blue shift.But how do we determine the distance?This excerpt is from Hawking's "The Universe in a Nutshell". So small and faint?I understand that this book is for the laymen, me, and doesn't go into too great of detail, but I was hoping some from this forum could help satiate my curiosity, Cavediver, maybe, or anyone else knowledgeable in astronomy or cosmology.Thank you, kindly. moved here by AdminJar{Note: Source of this message/new topic is here. - Adminnemooseus}This message has been edited by AdminJar, 04-25-2006 10:04 AMThis message has been edited by Adminnemooseus, 05-08-2006 03:53 PM

I'm not an expert here, but I think this is the basic outline.The distance to relatively near stars is determined by triangulation. Measure the angle of the star in mid summer, and measure it again in mid winter. Then you have a triangle. The base of the triangle is the diameter of earth's orbit around the sun (the line from the midsummer position to the midwinter position). The two base angles of the triangle have been measured. The apex of the triangle is the star whose distance is to be determined. Using trigonometry to solve the triangle gives the distance.For more distant stars, it is trickier. It turns out that there is a class of stars known as cepheid variables. The brightness of these stars depends on the rate of oscillation (variation rate). So, by measuring the oscillation rate, you can compute the brightness. Then you measure the observed brightness, which depends on actual brightness and distance. The scale for measuring distance with cepheid variables is calibrated by means of triangulation measurements for the nearest of these cepheids.For really distant stars, the Hubble red shift is used. It turns out (empirical observation) that the amount of red shift depends on the distance. The Hubble distance measurement is calibrated using the cepheid variable scale.I found a web page that seems to be a tutorial on measuring stellar distances.

Hi Inlixion NWR's already started you off on stellar distances. Parallax provides the starting point and methods progress in complexity from there. However, for the galaxies there is an even more simple starting point: simple observation!Look at the Andromeda Galaxy (M31). It is actually huge... four times the width of the moon on the sky! Observe it carefully and you will realise that it is made up of stars. Observe it carefully with a very large telescope and you will get a measure of how many stars.Making the most approximate guestimate for the minimum possible separation of those stars, and you get a feel for the actual size of Andromeda. You know what angle it subtends at the eye, you have a vague idea of how big it is, so you have a vague idea of how far away it is.In astronomy we are pleased when we are within an order of magnitude or two So Andromeda is somewhere between 100,000 and 10,000,000 light years away. Not bad for simple observation!

Hi nwr, cavediver.Very interesting material, although I would be lying if I proclaimed that I understand all of it. The tutorial was incredibly helpful, though, nwr, and I appreciate it greatly.But one fact I couldn't get around: a light year is said to be a unit of distance, not time. But what little I remember from my 3 weeks in an astronomy class (the professor was difficult to understand) was that the further you looked into space, the further back in time the object you were viewing was, or is..?E.g. if we viewed a star that was 100,000 LY's away, the light that we saw now took 100,000 years to reach us. So, if the star were to explode, we would be oblivious to the fact for another 100,000 years. Is that correct? my gut says I'm missing something very simple.P.s I hope I'm not off topic.

Yes. The further stars are away from us, the older the images of them we are actually seeing. That's why deep space observations are considered one way to observe the universe as it was in the past.

Thanks EZ. Always a pleasure to hear from you.

The distance to the Triangulum spiral, Andromeda's neighbor, has also recently been measured by geometrical means, too. Brunthaler, at al, in Science 307, pp1440-1443 (2005) Similar methods also gave 7200 +/- 300 kiloparsecs to the galaxy Messier 106 a few years earlier. This galaxy's steep inclination to our line of sight made the error bars much smaller. (A kiloparsec is 3260 light-years).

I have learned so mush in the past few minutes reading this thread. I have nothing to offer in this as I am a compleate idiot on the subject, but thank you all for the enlightenment