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View Full Version : yes another question...about sun like stars...



sadishappy
2009-Aug-20, 09:04 PM
Hi again,
I've always wondered...
With the naked eye how many sun like stars can we see and how far away can we see them?

chornedsnorkack
2009-Aug-20, 09:17 PM
Roughly 50 lightyears.

But no star is an exact copy of the Sun. When is a star similar enough to count as "sunlike"?

sadishappy
2009-Aug-20, 09:34 PM
basically G star, same mass... :-) Quick response! thanks!

sadishappy
2009-Aug-20, 09:46 PM
yah, a G2 star (although I've also heard G V, is there a difference?)
In laymans terms... same size, mass, luminosity....

cran
2009-Aug-20, 10:08 PM
Hi again,
I've always wondered...
With the naked eye how many sun like stars can we see and how far away can we see them?

I've heard that the number of stars visible to the naked eye varies according to the location on Earth used as the observation point* -
with rough numbers ranging from 2500 up to 5000 stars ...

*eyesight might be a factor, also ...

how many are "sun-like"?
well, as indicated, that depends a great deal on what is considered "sun-like" ...

another unclear term is "our (stellar) neighbourhood", but a starting point for numbers of sun-like stars might be found in articles like this one:

http://www.space.com/scienceastronomy/milkyway_movement_040406.html

The Crazy Cosmos: Stars Near Sun are Wild & Wayward
By Robert Roy Britt (http://www.space.com/php/contactus/feedback.php?r=rb)
Senior Science Writer
posted: 12:45 pm ET
06 April 2004


European astronomers spent 15 years making 1001 nights of observations to detail the motions of more than 14,000 stars that are currently in the solar neighborhood, a tiny corner of the Milky Way...

The observations were made with the Danish 1.5-meter telescope at the European Southern Observatory in Chile and the Swiss 1-meter telescope of the Observatoire de Haute-Provence in France...

Additional observations were made at the U.S. Harvard-Smithsonian Center for Astrophysics. The research will be detailed in the journal Astronomy & Astrophysics.
This census, which involved only Sun-like stars, also catalogued each star's age and chemical makeup. In addition, about one-third of the stars were found to have one or more stellar companions, a ratio that does not surprise astronomers. NB-bolding mine

Nick Theodorakis
2009-Aug-20, 10:29 PM
Hi again,
I've always wondered...
With the naked eye how many sun like stars can we see and how far away can we see them?

With a few exceptions, such as alpha-Centauri, most of the bright stars we see by naked eye have a much higher intrinsic brightness than the sun. The sun has an absolute magnitude of about 4.7-4.8 (depending on which reference), which is how bright it would look at 10 parsecs (about 32 light years); this would be just barely visible to an observer in a moderately light-polluted site. I would guess that no sun-like star will be naked-eye visible past 40 or 50 light-years.

Here is a list of "sun-like" stars (http://en.wikipedia.org/wiki/Solar_twin) from wikipedia; depending on how you define "sun-like" and how dim you think you can see, there doesn't seem to be much more than 20 or so of them visible to the naked eye.

Nick

TonyE
2009-Aug-20, 10:56 PM
The Bright Star Catalogue lists 18 stars of spectral type G2V (like the Sun) and magnitude brighter than 6.5. Only one of them would be easily visible - Alpha Centauri at mag 0.01. All the others are fainter than mag 5.

sadishappy
2009-Aug-20, 11:00 PM
Sweet. This is the best forum ever! :-) What great responses already.

TonyE
2009-Aug-21, 12:03 PM
yah, a G2 star (although I've also heard G V, is there a difference?)
In laymans terms... same size, mass, luminosity....

The "G2" specifies the spectral class of the star and says that it's colour/surface temperature are similar to the Sun.

The "V" specifies the Luminosity Class and says that the star is a "main sequence dwarf" like the Sun.

"Main Sequence" means that the star is in its Hydrogen-to-Helium converting period where it will spend most of its life.

Main sequence stars of the same colour/temperature are of a similar mass.

"Dwarf" is a odd word to use for a star but is generally used for all stars that are of a normal size for their mass. As opposed to "Giant" that means it has swollen up to be much bigger than normal - something that stars do in their old age.

fifelad55
2009-Aug-21, 04:42 PM
With a few exceptions, such as alpha-Centauri, most of the bright stars we see by naked eye have a much higher intrinsic brightness than the sun. The sun has an absolute magnitude of about 4.7-4.8 (depending on which reference), which is how bright it would look at 10 parsecs (about 32 light years); this would be just barely visible to an observer in a moderately light-polluted site. I would guess that no sun-like star will be naked-eye visible past 40 or 50 light-years.

Here is a list of "sun-like" stars (http://en.wikipedia.org/wiki/Solar_twin) from wikipedia; depending on how you define "sun-like" and how dim you think you can see, there doesn't seem to be much more than 20 or so of them visible to the naked eye.

Nick

I was trying to view the stars with binoculars last night and whilst my eyes were not properly dark adapted, stars of magnitude 3 were barely visible through binoculars. I had to use a stellarium programme to identify which stars I could see with the naked eye. They were Vega and Deneb to the north and Altair not far off being overhead. (I live at lattitude 13 degrees north).

Alpha Centauri is, in theory, visible from where I live but must be very difficult to spot due to being low in the sky and the horrendous light pollution here.

Alan

cran
2009-Aug-21, 04:49 PM
Alpha Centauri is quite the stand-out star where I live -
little country town in the southern hemisphere (don't recall the lat offhand) -
visually, its nearest rivals for brightness down here are Venus and Jupiter ...

TonyE
2009-Aug-21, 05:07 PM
Alpha Centauri is quite the stand-out star where I live -
little country town in the southern hemisphere (don't recall the lat offhand) -
visually, its nearest rivals for brightness down here are Venus and Jupiter ...

Lucky you:lol: Can't see it at all from here :cry:

chornedsnorkack
2009-Aug-21, 05:22 PM
Alpha Centauri is quite the stand-out star where I live -
little country town in the southern hemisphere (don't recall the lat offhand) -
visually, its nearest rivals for brightness down here are Venus and Jupiter ...
What about Canopus?

cran
2009-Aug-21, 07:05 PM
What about Canopus?

it's just possible that I meant Canopus ... :shifty:

there's a reason I'm a budding rock doctor,
and not a rocket scientist ...

sadishappy
2009-Aug-21, 07:09 PM
The "V" specifies the Luminosity Class and says that the star is a "main sequence dwarf" like the Sun.

Good to know. I thought that the "G" covered luminosity too.

AndreasJ
2009-Aug-21, 08:27 PM
The "V" specifies the Luminosity Class and says that the star is a "main sequence dwarf" like the Sun.

Good to know. I thought that the "G" covered luminosity too.

'G' and 'V' in combination give you the luminosity - how stars of the same luminosity class but of different spectral classes are of different absolute brightness (but 'V' stars of any spectral class are near the typical brightness for that spectral class). The WP page (http://en.wikipedia.org/wiki/Stellar_classification) on stellar classification has more detail.

The system is, certainly, not terribly intuitive for laymen, but it makes a lot of sense in terms of stellar evolution.

fifelad55
2009-Aug-24, 06:12 AM
I can see Canopus clearly from here at certain times of the year.

Alan