If I’d Known Then What I Know Now: Nights with a 60mm Refractor

OLD SCOPE & Company

The “Old Scope,” a name it acquired during discussions of its history and use on the Cloudy Nights forum, is a refractor-type telescope with a 60mm aperture, 700mm focal length, and a focal ratio of f/11.7. It was purchased in the summer of 1970.

The theoretical limiting magnitude for stellar objects for the Old Scope works out to 11.6, but in reality, stellar objects fainter than about 9.5 are difficult to pick up under suburban observing conditions. Under transparent skies at a darker sky site (Bortle 4.5 or better) the performance of the telescope approaches the theoretical limit, but anything fainter than magnitude 10.5 remains a serious challenge.

The Old Scope is currently mounted on an Orion AstroView Equatorial telescope mount equipped with a Right Ascension drive.

Eyepieces used:

Type

Focal Length mm

AFOV °

TFOV ‘

x

Orion Lanthanum

9.5

50

20.5

74

Orion Sirius Plossl

40

43

143.3

18

Orion Sirius Plossl

25

52

111.4

28

Orion Sirius Plossl

10

52

44.6

70

Orion Sirius Plossl

6

52

26.6

117

Celestron SMA

17

52

76

41

UO Orthoscopic

9

47

36.2

78

UO Orthoscopic

6

47

24.1

117

UO Orthoscopic

4

47

16.1

175

TMB Planetary

8

58

40

87

TMB Planetary

4

58

19.9

175

Nagler

4.8

82

33.7

146

A 2x Barlow lens is often used, and the Old Scope is equipped with a Rigel Quikfinder.

Most commonly used star charts are the Sky & Telescope Pocket Star Atlas (“jumbo” edition), the Bright Star Atlas by Wil Tirion and Brian Skiff, and the Cambridge Double Star Atlas, first edition, by James Mullaney and Wil Tirion. For lunar observing, the primary resource is Atlas of the Moon by Antonin Rukl. See the bibliography page for a more complete list of references used.

 

Observations (by date)

25 August 2019

Eyepieces Used: 25mm Plossl (28x), 10mm Plossl (70x), 6mm (117x), 9.5mm Orion Lanthanum (74x)

Delphinus (Del)

Gamma (γ) Del: I picked up a hint of color contrast with this pair when I first found it in the 25mm eyepiece, but needed to bump the magnification up considerably (6mm) to really appreciate the sight. This is often the case when a color contrast is subtle; magnification, and sometimes putting them double star slightly out of focus, will make colors easier to perceive. The primary star was pale yellow, and the companion was an equally quiet shade of blue. The difference in magnitude was also subtle, about half a magnitude, but was visible. A pretty pair, and one I will very likely revisit in the future.

Alpha (α) Del: Olcott’s Field Book of the Stars lists this as a binary, but Muirden’s Amateur Astronomer’s Handbook does not. A check of the Cambridge Double Star Atlas (either edition) does not show it as a double star, either, but Carte du Ciel and the Washington Double Star Catalog (the catalog used by CdC to display doubles) list two faint companions. The listed companions are 12th and 13th magnitude stars that, under the best conditions, are beyond the light grasp of the Old Scope. I put it in the 25mm eyepiece all the same, since it was on the list from Olcott’s book, and I have this thing about revisiting the sights to which that book led me, so many years ago. Back then I likely looked at it and was puzzled by the lack of a visible companion. Now I know to appreciate the sight for what it is, a lovely gem of a star. It’s never a mistake to look at a star with a telescope in any case. This one is a pretty white star with a clear blue cast to it, set in a sparse field of much fainter stars.

Corona Borealis (CrB)

Zeta (ζ) CrB: Not every double star shows duplicity when found in the low power eyepiece (25mm Plossl) that I use to locate objects. The only hint this one gave when located was the appearance of not being completely in focus. The 10mm Plossl provided reassurance that I’d found the right star, but it took the 6mm Plossl to get a really good look. There’s a full magnitude difference between the brightness of the A and B star, with A being white and B washed out but having a touch of warmth to it. If they’d been further apart, I suspect there would have been a nice color contrast.

STF 1964 AC: Found and split this one with the 25mm Plossl, but observed it with the 10mm Plossl. These stars are listed as being of exactly the same magnitude, a pair of magnitude 8 sparks side by side, with no real color to them. Grayish-white points of faint light. An interesting sight, but not especially showy.

Sigma (σ) CrB: I could definitely see that this duo deserved that label when I found them with the low power eyepiece (25mm Plossl). However, the 10mm Plossl gave a better view, displaying the magnitude contrast, which was obvious, and a near complete lack of color. Both were sort of off white, with the fainter companion on the gray side.

Pegasus (Peg)

1 Peg (STFB 11 AB): Locating this star provided a reminder that I still have a few things to learn about navigating the night sky. Pegasus had just come up high enough for my back yard observing location, and was in an orientation I wasn’t accustomed to at all. This led to an embarrassing amount of confusion as I tried to verify the location of 1 Peg. But I eventually found it and put it in the 25mm Plossl. I immediately had my doubts about this being the right star. There may have been a spark of light where the companion should have been, but even with averted vision it was not consistently visible. With the 10mm Plossl in place I was reassured. The companion star was there, a colorless speck of light in the darker sky of the higher power eyepiece. The primary star beside it was itself an unremarkable object. The difficulty I experienced seeing clearly that companion star made it plain that the “theoretical limiting magnitude” I have for the Old Scope is not entirely reliable. At 9.3, the companion star was almost two magnitudes brighter than the 11.6 the number crunching provides. I could barely see it.

M15 (NGC 7078): While using binoculars to verify the position of 1 Peg, I swept up this globular cluster, an object I’ve enjoyed viewing in the 8″ Newtonian on several occasions. Since it was clearly visible in the 8×42 binoculars, even in a suburban sky, I decided to give it a try. It proved worth the effort. The best view came through the use of a 9.5 Orion Lanthanum eyepiece. M15 was a pale gray ball that faded away around the edges. It was ever so slightly brighter in the center when averted vision was used. A trio of relatively bright stars accompanied it in the field of view, making for a pleasing sight. Just goes to show you should always give the brighter deep sky objects a chance, even when observing from suburbia.

Epsilon (ε) Peg: Often labeled on charts as Enif or S 798 AC, I needed to plot this one and the stars around it, then use its position angle to be sure which of the stars in the field was really the magnitude 8.7 companion. The field in question was that of the 25mm Plossl, and the companion star was, in fact, visible. There’s a third star B star in this system that’s almost 13th magnitude, and my combination of aperture and eye failed to pick it up. In light of my experience with 1 Peg earlier in the evening, that’s not a surprise. The companion star was of an unremarkable appearance, but the primary component, Enif proper, is a pretty ruddy gold star that is worth aiming any telescope at for a few minutes, at least.

Andromeda (And)

M31 (NGC 224): The great galaxy in Andromeda is surely no object for light polluted conditions, and yet standing there with the Old Scope and recalling the night, long ago, when I observed a galaxy through that lens for the first time, I look at it now and then from my back yard. It would be easy to mistake it for a large globular cluster, but the slightly oblong shape gives it away. This is the core of the galaxy, and nothing more; all else has faded into the city sky. Still, there it is. A galaxy, seen in a 60mm refractor.

Pi (π) And: Also seen on some charts as H 5 17 AB, here’s another example of how knowing position angles can help. There were several other stars in the field, and although the nearest one seemed to be the correct magnitude and angular distance, it was the determination of the field’s cardinal directions (by allowing the A star to drift far enough to know which was was west) that verified its identity. Knowing which way is west in a refractor field of view, north is 90° clockwise. South and east become self-evident when you know north and west. With a position angle of 174°, the companion was revealed as the star nearest the primary. There was a clear magnitude contrast between the two, and both stars were whitish.

Gamma (γ) And: This duo is often compared favorably to Alberio in Cygnus, and in a larger aperture is does hold its own. With the Old Scope, I saw no hint of duplicity, hardly a surprise since this is a tighter double than Alberio. The 6mm Plossl gave the best look, and the gold and blue colors of the stars did make a pleasing contrast. This is a double star worth the effort, even with modest aperture.

Posted August 29, 2019 by underdesertstars

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