Amended double star tips

[bigjoe]

Amended double star tips

Double star tips

THIS WAS A LIST I COMPILED WITH THE HELP OF STEVE (Tinderboxsky), Matt t,bombardon and some others.

1: SEEING - Must be very good for tough doubles.

2: ALTITUDE - Well above the horizon in
a lot of instances.

3: APERTURE -Depends on separation, magnitudes.Cooled and well collimated scope ,though probably no more than 12" due to the affects of seeing on large obstructed scopes.

4: POWER - The use of it is necessary - Helps darken sky background, and with limiting magnitude ; 200x + may be needed.

5: USE A MASK - Hex , may be necessary.

6: ORIENTATION - Is your diagonal/scope displaying an UPRIGHT , EAST/WEST VIEW? ; If not adjust accordingly ; this is critical so you know what direction the secondary is.

7: PRACTISE:

8: DRIFTING - For a faint secondary.Is it preceding East or following West when your facing North?

9: WARM CLOTHING , and stool if necessary.

10: PATIENCE - and lots of it - It could take many attempts!

11: LESS GLASS - Use of EP with fewer elements 4/5 max to increase contrast and detection, may be of help.

12:AVERTED AND DIRECT VISION - Go back and forth between direct and averted vision, until the companion is held in direct view.

13: ZOOM EP - Use of a good marked zoom EP, to find the optimum power for the seeing and filters if necessary.*

14:HIGHLY ACCURATE FOCUS - TOGETHER WITH A NICE FLAT FIELD, FREE OF CURVATURE - this is a must also , and you may have to re-focus often.

15:VERY STABLE MOUNT - Absolutely no wobbles!*

16:VIEWING AT TWILIGHT - Can reduce the glare of a bright primary EG : Sirius A - and this goes for other bright primary doubles as well!

17:KNOW YOUR FIELD-Know what say 10" arc looks like in your go to eyepieces for example as in Sirius.
Formula for working this is OCULAR FIELD IN MM X 57.3 DIVIDED BY FOCAL LENGTH OF SCOPE IN MM.
EG: EP Has field stop of 3 mm and scope 1719 mm focal length

Then that is simply ( 3 x 57.3 )÷ 1719 = 1/10 degree true field of view or 6 mins arc or 360" -So if a double has a separation of 36" it will be one tenth of the field width so you'll get an idea were the secondary will be!

18: Position angle is taken as I've said from an imaginary line on the celestial sphere due North , increasing North to East in a clockwise direction - East following (will be on the right if you face North) -an example is in Sirius B being roughly around 90 degrees or more position angle theta East at this moment in time, and simply let Sirius b drift into the field of view if you let A go past your left West field stop so its glare is mitigated and its worth a crack every good night now!!

19: HOOD or COWL; this WILL help if streetlights or other bright light sources are a nuisance -- I rarely observe without one in any case.
Hope this helps.
PS: If anyone knows of more tips that have not come to our attention please lets us know!

[The Mekon]

I have been viewing double stars since 1969 - this is a great list for those who wish to make the best observations. Many thanks.

[Ric]

A good list Joe, thanks for the write-up.

[bigjoe]

Thanks Ric glad I can help some get into this terribly neglected part of AA.
bigjoe

[bigjoe]

Thanks also John.
I'm sure you also would have an equally or similar list of these shamefully neglected Astro Gems, some of the colour contrasts are stunning, and there's also blood red Carbon Stars in some of them!!
bigjoe

[Atmos]

I do keep reading that larger apertures affect seeing more than smaller ones... is it more so magnification than aperture?

I find using my 4" F/9 refractor and binoviewers far more comfortable than my 12" dob. Probably not the best with all of the extra elements and prisms etc :)

[bigjoe]

I agree Colin that too much aperture is not a good thing; a big lens/mirror trying to reach thermal equilibrium with big temperature deltas is nye impossible!
For some reason once you go past about 12" aperture for doubles its very difficult, as seeing also really affects big scopes not to mention the secondary star could also be occulted by a diffraction spike as well!!
And the high quality Tak optics with no central obstruction is going to make it easier during average seeing ; binoviewers should help also.
Your comfortable and you stand a better chance!!
Cheers bigjoe.

[bigjoe]

I should add that nearly all the doubles I mentioned in my other post, should be well within the reach of a 90mm-100mm scope with good collimated optics , thats reached equilibrium , under good seeing, and well above the horizon.
bigjoe.

[gaseous]

So all things being equal, an 8" dob would be better for doubles than a 16" dob?

[bigjoe]

Sounds strange but during average seeing the smaller aperture could be less affected!! And thus you stand a better chance as the image is not dancing around all over the place, and obscuring the secondary star ; also can depend on size of secondary obstruction
The larger objective/mirror system could also have not reached thermal stability , when the other already has!! No waiting for hours either.
bigjoe.

[bigjoe]

BTW position angle is notated as theta in degrees and separation rho arcseconds .
Position angle is measured from the line going to celestial north, and increases through east in aclockwise direction. North is the meridian at 0° position angle, east(following) is on the right at 90° position angle, and west (preceding) is on the left at 270° position angle


bigjoe

[bigjoe]

[Position angle is taken as I've said from an imaginary line on the celestial sphere due North , increasing North to East in a clockwise direction - East following (will be on the right if you face North) -an example is in Sirius B being roughly around 90 degrees or more position angle theta East at this moment in time, and simply let Sirius b drift into the field of view if you let A go past your left West field stop so its glare is mitigated and its worth a crack every good night now!!


bigjoe

[bigjoe]

Double star tips

THIS WAS A LIST I COMPILED WITH THE HELP OF STEVE (Tinderboxsky), Matt t,bombardon and some others.

1: SEEING - Must be very good for tough doubles.

2: ALTITUDE - Well above the horizon in
a lot of instances.

3: APERTURE -Depends on separation, magnitudes.Cooled and well collimated scope ,though probably no more than 12" due to the affects of seeing on large obstructed scopes.

4: POWER - The use of it is necessary - Helps darken sky background, and with limiting magnitude ; 200x + may be needed.

5: USE A MASK - Hex , may be necessary.

6: ORIENTATION - Is your diagonal/scope displaying an UPRIGHT , EAST/WEST VIEW? ; If not adjust accordingly ; this is critical so you know what direction the secondary is.

7: PRACTISE:

8: DRIFTING - For a faint secondary.Is it preceding East or following West when your facing North?

9: WARM CLOTHING , and stool if necessary.

10: PATIENCE - and lots of it - It could take many attempts!

11: LESS GLASS - Use of EP with fewer elements 4/5 max to increase contrast and detection, may be of help.

12:AVERTED AND DIRECT VISION - Go back and forth between direct and averted vision, until the companion is held in direct view.

13: ZOOM EP - Use of a good marked zoom EP, to find the optimum power for the seeing and filters if necessary.*

14:HIGHLY ACCURATE FOCUS - TOGETHER WITH A NICE FLAT FIELD, FREE OF CURVATURE - this is a must also , and you may have to re-focus often.

15:VERY STABLE MOUNT - Absolutely no wobbles!*

16:VIEWING AT TWILIGHT - Can reduce the glare of a bright primary EG : Sirius A - and this goes for other bright primary doubles as well!

17:KNOW YOUR FIELD-Know what say 10" arc looks like in your go to eyepieces for example as in Sirius.
Formula for working this is OCULAR FIELD IN MM X 57.3 DIVIDED BY FOCAL LENGTH OF SCOPE IN MM.
EG: EP Has field stop of 3 mm and scope 1719 mm focal length

Then that is simply ( 3 x 57.3 )÷ 1719 = 1/10 degree true field of view or 6 mins arc or 360" -So if a double has a separation of 36" it will be one tenth of the field width so you'll get an idea were the secondary will be!

18: Position angle is taken as I've said from an imaginary line on the celestial sphere due North , increasing North to East in a clockwise direction - East following (will be on the right if you face North) -an example is in Sirius B being roughly around 90 degrees or more position angle theta East at this moment in time, and simply let Sirius b drift into the field of view if you let A go past your left West field stop so its glare is mitigated and its worth a crack every good night now!!

19: HOOD or COWL; this WILL help if streetlights or other bright light sources are a nuisance -- I rarely observe without one in any case.
Hope this helps.
PS: If anyone knows of more tips that have not come to our attention please lets us know!

[Steffen]

Not strictly an observing tip, but:

Familiarise yourself with the StelleDoppie (http://stelledoppie.goaction.it/index2.php?section=1) website. It basically presents the WDS and other double star catalogs as a searchable database. I find it very useful for looking up present and future separation of doubles (Alpha Cen (http://stelledoppie.goaction.it/index2.php?iddoppia=60453) for example is just going through a minimum in separation) and for creating observing lists. It has an extensive advanced search function that lets you find doubles by a long list of criteria.

For making observing lists I often use searches like "constellation Cetus, magnitude of secondary component mag9 or brighter, separation between 0.5 and 30 arc seconds". Search results can be saved as lists in Sky Safari, CdC or CSV format.

[bigjoe]

Thanks for bringing this to our attention Steffen.
Yes a great way for all to actually use the Washington Double Star Database. .
One can input what variables one is looking for, a particular range of magnitudes for their aperture etc.Esp useful for those with smaller scopes that are magnitude limited to all but the brighter ones and want to get a taste for what there scope is capable of.

PS: AND glad to see your knowledge on doubles and needed input here once again Steffen !
VIELEN DANK MEIN FREUND. bigjoe.

[bigjoe]

Just amended some tips
bigjoe

[Bombardon]

For the benefit of Bigjoe and his 'trickledown' followers, I have included a short list of easy doubles near Pointers and Crux. More will follow when the snail weather along the east coast clears. Thanks Bigjoe for keeping this up and for the useful sites:

Around the Southern Cross 1. (10"F5 Dob)
1) Delta (Δ) 159.Centauri: [RA 14.22.6; Dec -58.28; mag 5/7.6 Sep 9.1” PA 157°] Most of us are all too familiar with The Pointers but nearby and forming the apex of a triangle on the north side of the pointers lurks this fine double star . Through a small telescope this mag 5 yellowish star has a blue companion easily spotted at moderate power.
2) Delta (Δ) 141; Q Centauri: [RA 13.41.7; Dec -54.34’mag 5.2/6.5 Sep 5.4” PA 163.]This mag 5 golden star and its 6.5 mag companion lie just south of Epsilon Centauri (ε), which itself forms the apex of a triangle with the pointers. Although closer than the last pair at 3.4” separation, in steady atmosphere the rose coloured companion is just separated at moderate power. Q itself forms a neat triangle with two other fainter stars in the field.
3) Delta (Δ) 133; J Centauri: [RA13.22.6;Dec -60.59’ mag 4.5/6.2 Sep 61” PA 345]This 4.5 and 6.2 pair lie about halfway between Beta Centauri (the westerly Pointer) and Mimosa or Beta Crux. It lies just south of an ‘L’ shaped group of mag 5 stars. This is a wide pair suitable for small optics and the colour contrast of White and Blue is pretty. Another star lies in the field.
4) Delta (Δ) 126; Mu (μ) Crucis: [ RA 12 54.6 Dec -57 11; mag 3.9/5.0; Sep 37” PA 24]Yet another fine Dunlop double is found just over the border in Crux and this one lies at the apex of a triangle formed with Gamma and Beta Crucis. This very light yellow mag 3.9 star is an easy separation from its light blue mag 5 companion at a wide 37”. The view is rich with two other stars in the field at moderate power.
5) Delta (Δ) 252; Alpha Crucis:[12 hr 26.6m; -63 06 S, mag 1.4 and 1.9, sep 4” PA 110, and C star mag 4.9, sep 90”].
Finally, no search for double stars in this area of sky is complete without turning your instrument to a stunning binary. In finder scope and binoculars Acrux is a delightful brilliant white star with a wide blue companion. The telescope reveals that the brilliant ‘A’ star can be split into a fine binary ‘A 1 and A2’. The period of this pair is a whopping 1,500 years. Further spectrum analysis reveals ‘A1’ is an eclipsing binary with an orbit of 76 days! Acrux is 25,000 times brighter than our sun and 320 ly away.
The wide third blue companion ‘C’ is also a binary and nearby fainter stars are now thought to be related. This is truly a stunning multiple system. I found alpha hard to split at high power but my 4” offset mask revealed two clean points of light. Eugene

[bigjoe]

Thanks for this list Eugene . Alpha Crucis is one all ahould look at as well as Alpha centauri, Gamma leonis, Porrima (Gamma Virginis ), Izar (Epsilon Bootis), Almaak ( Gamma Andromedae), h3945 in Canis Major , Alnitak , Sigma and Theta Orionis and of course Albireo in Cygnus. Those are for the beginner but not enough actually even see these!!


With thanks bigjoe .

[bigjoe]

BTW . Just got back from a busy time in Melbourne and have been slow to respond ; so my apologies.
bigjoe.