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Home > Articles > How To > Beginners > Colorful Double Stars for the ST80

Colorful Double Stars for the ST80
By Blair Slayton - 9/11/2005

My seeing conditions during the last few months have not encouraged DSO hunting and observing so I have developed an interest in viewing colorful double stars. Many like the challenge of splitting doubles but in observing colorful doubles I look for the power that gets a nice separation yet keeps the stars close enough for a nice contrast.

My equipment is Orion’s ST80 on Orion’s AZ-3 mount.
This is a list of colorful double stars (and one multiple star set) that the short focal length of the ST80 (and those popular 80mm scopes of 480mm focal length) really helps in keeping them close enough for a nice contrast or is within range of this scope.

Also, most of these are visible by naked eye even in somewhat light polluted skies like those around Greensboro, NC.

Note: by the star in parentheses is the primary and secondary magnitude.

The first on this list is Albireo (3.1,5.1) in Cygnus. I like this nice double at about 12X. I find the separation a bit much at about 25X to 30X which is the lowest power of many refractors and SCT scopes.

The next is Cor Caroli (2.9, 5.6) in Canes Venatici which is nice at about 30X. The contrast in this pair is more subtle than Albireo’s. As a side note, the bright core of galaxy M94 is only 3 degrees from Cor Caroli and is often visible in the ST80 at about 40X.

Another double with a very strong contrast is Almach (2.1,4.8) in Andromeda which has a good separation at about 50X.
Another low power double (about 15X) is Delta (3.5,6.3) Cepheus which is subtle in color contrast like Cor Caroli.

My southern skies are pretty much washed out by Greensboro at altitudes below about 40 degrees yet I still can find and enjoy Beta (2.6,4.9) Scorpius at about 44X.

The one multiple star system is Omicron (3.8,4.8,7.0) Cygnus which even at 13X is too far separated for me but is still nice to visit. I usually begin my sweeps of this star filled area with Omicron.

Mintaka (2.2, 6.8) Orion is another low power double (about 12X). This star is in Orion’s belt area and is on one edge of Cr 70 which is an Open Cluster of about 150 minutes in size and only a scope like the ST80 can see all of Cr 70.

I’ll finish this introductory list with my favorite double for the ST80, Rasalgethi (3.5,5.4) in Hercules. Besides a very striking contrast this double looks best at about 100X and at this power the stars turn into round balls of color where at lower powers the stars look more like sparklers.

On the eyepieces to use with the ST80 or like scopes I have found that Orion’s Sirius Plossls (32mm and 26mm) work very well. I also like the 20, 15 and 9mm Expanse eyepieces. But I have found that starting at 7mm Plossls and Orthoscopics just have too little of eye relief. I have found Vixen’s LV series with 20mm of eye relief a good deal though they are over $100 a piece when bought new. I have the 7, 6, 5 and 4mm. Another very good eyepiece is Televue’s 6 to 3mm zoom which maintains a 50 degree FOV and 10mm of eye relief through all focal lengths. At first look the $380 price can be a shock but since it is equal to 4 eyepieces (it has click stops at 6,5,4, and 3mm) that drops the price to $95 a piece.

So if you have a rich field scope collecting dust in the corner, hopefully, this article will renew your love affair with it.

Blair Slayton
September 2005

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