Author Topic: Dumb question but what is a Double Star and how do you find them?  (Read 132 times)

Dennis Collins

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Re: Dumb question but what is a Double Star and how do you find them?
« Reply #15 on: January 21, 2018, 03:29:48 AM »
The very first double star that I ever saw was Mizar (and Alcor), which marks the middle star in the middle handle of the Big Dipper asterism. Mizar and Alcor, also called the horse and rider, are visible without optical aid, if your skies are reasonably dark. Mizar is itself a double star and is reported to be the first ever double star seen through a telescope.

If you choose to check it out, you should see two pure white stars, like two eyes staring back at you. What I find amazing is that in that "tiny" space between those two stars, there is enough room to fit six solar systems, fitted end to end.

A little more info here, if you're interested.

http://earthsky.org/...horse-and-rider

Stanley Elliott

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Re: Dumb question but what is a Double Star and how do you find them?
« Reply #16 on: January 23, 2018, 01:32:44 AM »
Quote
<p class="citation">Quote
It's probably true that most of the entries in the enyclopedic Washington Double Star catalog are visual doubles rather than true binaries.
From what I know, it's actually the other way around. I think it was proven statistically, that the number of faint stars close to one another is much greater than what should have been the case, had they been distributed at random.[/quote]

i believe i am the first (perhaps still the only) person to actually perform an audit of the WDS, using the available information in WDS and parallax or distance data from hipparcos. the results are here. i think you'll find them useful.

the better term is not "visual double star", a phrase coined by the astronomer robert grant aitken to distinguish them from spectroscopic binaries. the standard term is "optical pair", which makes no claim as to whether the pair is gravitationally bound or not. as a fan of clear speaking, i've innovated the term "pair asterism" to indicate optical pairs that we know from observational evidence have nothing to do with each other.

some will claim that pair asterisms are also double stars, but that usage dropped from professional astronomical usage around 1900. wulff heintz titled his 1978 book "double stars" and sneered at the other stuff as "perspectivic objects". SIMBAD, the authoritative global astronomical database, uses the term "double or multiple star" to refer to gravitationally bound systems, and "single star" or "star" to refer to everything else.

Prasanna Patel

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Re: Dumb question but what is a Double Star and how do you find them?
« Reply #17 on: January 23, 2018, 03:04:15 AM »
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True double stars are gravitationally linked and relatively close to each other. "Visual doubles" are stars that happen to be in nearly the same direction so appear to be close together but are actually far apart. A list of double stars will include only gravitationally linked stars.


this is true, and surprisingly there is only one field guide to double stars that adheres to this principle: the CDSA2.

the introduction also describes the physical origin of double stars, their dynamic evolution and hierarchical structure, and much more. all that is background knowledge necessary to appreciate these amazing systems -- really the "keystone species" of galactic evolution.

aninerti

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Re: Dumb question but what is a Double Star and how do you find them?
« Reply #18 on: January 25, 2018, 06:57:11 PM »
Whatever category the double star may be, they sure arepurrdy to look at.
I always put at least a handful in my observing lists. I think rho Oph (summer)
and beta Mon (winter) are my current favorites but these are multiple stars
(more than two) and are in the same lists as double stars. Besides double stars
often have invisible companions that can be detected spectroscopically but
not visually. They are all different and beautiful.

Christopher Mendez

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Re: Dumb question but what is a Double Star and how do you find them?
« Reply #19 on: January 26, 2018, 01:57:25 AM »
The next time you are setting up that TEC 140 take a close look at Polaris...it's double, a blue-white star, shining at mag +9, is located about 18.6" away.

Todd Topcic

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Re: Dumb question but what is a Double Star and how do you find them?
« Reply #20 on: January 31, 2018, 05:30:14 AM »
Here is page to check for doubles by Constellation. http://astronomy.eag...ry.org/doubles/

Jerry Gilbert

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Re: Dumb question but what is a Double Star and how do you find them?
« Reply #21 on: January 31, 2018, 08:58:03 AM »
Quote
Whatever category the double star may be, they sure arepurrdy to look at.
I always put at least a handful in my observing lists. I think rho Oph (summer)
and beta Mon (winter) are my current favorites but these are multiple stars
(more than two) and are in the same lists as double stars. Besides double stars
often have invisible companions that can be detected spectroscopically but
not visually. They are all different and beautiful.

All unique and purrdy indeed.
I always make it a point stop and visit the doubles/multiples along the way to, and in the neighborhood of the fuzzies as well.

Tyson Conway

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Re: Dumb question but what is a Double Star and how do you find them?
« Reply #22 on: February 02, 2018, 05:42:04 PM »
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One of the nice things about doubles is that you can generally study them from the city.

Alex

They are part of any full or partial Moonlit night under rural sky for me.
Plus part of urban outreach because they do work well from in the city.

Michael Thompson

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Re: Dumb question but what is a Double Star and how do you find them?
« Reply #23 on: February 02, 2018, 06:52:00 PM »
....and they can be viewed and enjoyed with anything from binoculars
to giant observatory scopes.

teirazaro

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Re: Dumb question but what is a Double Star and how do you find them?
« Reply #24 on: February 02, 2018, 10:17:56 PM »
Greg N. Thanks for posting that link, - Just ordered a copy of that book. It looks like it would be very handy for quick reference of what to look for at any given night. Thomas M

Michael Timmons

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Re: Dumb question but what is a Double Star and how do you find them?
« Reply #25 on: February 02, 2018, 11:28:01 PM »
Bright Star Atlas also makes a great broad sky reference companion/compliment to deeper field atlases like Uranometria.

xacypcheati

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Re: Dumb question but what is a Double Star and how do you find them?
« Reply #26 on: February 03, 2018, 03:16:57 AM »
http://www.cloudynig...star-observing/

At the risk of stating the obvious, this part of CN offers a wealth of info on doubles... apologies Jon, just reREAD all the posts carefully &lt;doh moment&gt;

plethenofin

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Re: Dumb question but what is a Double Star and how do you find them?
« Reply #27 on: February 08, 2018, 07:26:18 PM »
Just a mention here.

One of my favored is companion to Polaris our North Star. Tho its about a slightly dim 8 magnitude just off the glare of Polaris, a very fun view.

Use it alot to check the current sky conditions.

Also a decent test for the smaller scopes.

satimoja

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Re: Dumb question but what is a Double Star and how do you find them?
« Reply #28 on: February 09, 2018, 09:54:30 AM »
As you hsve read in earlier posts doubles can be gravitationally linked or visual by being nearby. I enjoy them a lot because you can see most even from light polluted skies and seeing does not have to be perfect for most except the very tightest. Once you start viewing them you will get hooked. I especially enjoy some of the more colored pairs. Make a list and start hunting.