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Some additional Observations of doubles in Cancer & Lynx

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Observation Report 10/04/06

Period 21:00 UT – 22:30 UT

Seeing – 2/ 5

Transparency 2/5

Targets –Listed in RA

Zeta Cnc (STF1196)


24 Cnc (STF STF1224)


Epsilon Hydra


STF 1334



After having got home from a pleasant if cold day in Brighton visiting friends, I put the scope out too cool at 7.30 PM (UT) [this is 8.30pm on BST] and had some dinner, you can’t observe on an empty stomach.

The Moon was a bright waxing gibbous and I wanted to take a pic of the Gassendi A crater but as the moon was behind the large tree in my neighbour’s garden I started with Saturn.

To assist anyone interested in observing doubles I have created a scale similar to William Herschel. I will define the ease (or difficulty of a split)

1/5 – Very easy wide pair both components bright.

2/5 – Easy pair closer separation and possibly unequal components.

3/5 – Close pairs of equal brightness.

4/5 – Close pairs of unequal brightness.

5/5 – Very close pairs, <1 arc second.

I hope this gives some guidance on what pairs anyone may want to observe.


The seeing was not great. I started with the 9mm Ortho (x133) and I could see the Cassini division and 5 satellites. Titan was west of Saturn. I pushed the scope to x266 but the image became soft. This was probably the combination of poor seeing and the scope not being fully at ambient temperature.

Zeta Cnc (STF1196)

RA 8:12:12.7 DEC 17:38:53 (AB 5/5) (AB-C 2/5)

I thought I would have a look at Zeta Cnc to see if the close pair could be split. I was not sure the split would be possible but I was pleased to find that at x266 the tight pair was a clear split with 2 stars nestled next to each other. The split was not as clear as on the 3rd of April again all 3 stars had an orange hue.

24 Cnc (STF1224)

RA 8:26:39.8 DEC 24:32:03 (AB-C 3/5)

This is a pair of white stars about 6” apart the PA is 49 degrees (the secondary is NE of the primary). I split it using the 12.5mm Vixen Ortho eyepiece giving x96 mag. Both stars are about Mag 7 so are not in the Norton star atlas. They can be easily found by going about a third of the way from gamma Cnc to ward iota Cnc. You can see 3 stars in line to the west of this point; these are nu2, nu1 and 28 Cnc. Just to the North West of 28 Cnc is 24 Cnc, it will be easy to see in a finder scope.


RA 8:35:51 DEC 06:37:13(A/B 2/5)

This is another pair that should be easily split at 10”. Using the 12.5mm Vixen Ortho (x96) the two components were easily separated. Secondary is again to the North East of the Primary (25 degrees).The primary was white with a hint of yellow and the secondary was white. This fits well with the F8V/G5V of the spectral class of this pair.

Although the primary is mag 6 it does not appear on the Norton Map which is an oversight. STF1245 is just inside the border of Cancer but the easiest way to find it is from the head of Hydra. If you point your scope at delta Hyd STF1245 is about 1 degree north and at Mag 6 should be easily visible through a finderscope.

Epsilon Hydra (STF1273)

RA 8:46:46.6 DEC 6:25:08 (AB-C 4/5)

As I was close to Hydra I had a quick look at Epsilon. It was not an easy split as the primary was wobbling. At x266 the secondary could be clearly seen to the North West of the Primary.

This is a double more suited to steadier nights. As the close separation of 3” means the secondary can get overwhelmed by the primary.


RA 9:18:25.9 DEC 35:21.50 (A/B 3/5)

STF1333 can be found easily between Alpha Lynx & 38 Lynx. It is about midway and slight west of a line drawn between Alpha & 38.

Again this pair took x266 to spit due to the poor seeing. I have checked the spectral class and it is A8V which fits well with the white colour I observed with this pair.

(In between 38 & Alpha Lyncis is another double STF1333. This is a magnitude 6 tight white pair. I had estimated the PA as 40-50 degrees & separation 2” (WDS - 49/1.8”). Although this pair is tight because the stars are of nearly equal magnitude they can be split more easily than would be expected.) – previous observation

38 Lynx (STF1334)

RA 9:18:50.6 DEC 36:48:10 (A-Bb 4/5)

I wanted to return to Lynx and re-observe the 3 pairs I had logged earlier.

38 Lynx can be found easily to the North East of iota Cnc or you can extend the constellation lines from gamma gem through beta Gem and a similar distance beyond and Alpha Lynx & 38 Lynx are the only 2 bright stars visible. Du to the poorer conditions I was not able to split the pair at x133 as I had last time but it took x266 to split them clearly.

(38 Lyncis is a tight split at x133 in the 8 inch scope but was easy at x266. The Primary is white with the secondary appearing pale yellow/orange to my eyes. I had estimated the separation as 4” and the last measure had it at 2.7”. I put the PA at around 200 and the last measurement was 225 degrees.) – previous observation


RA 9:20:59.4 DEC 38:11:17 (A/B- 5/5)

This was a very tough split tonight. STF1338 can be found a couple of degrees to the North East of 38 Lynx although both components are fainter than mag 6.5 their combined Mag is bright enough for them to be in Norton’s. I have checked their spectral class and at F2V & F4V off-white is a good match

(The final pair was a much tougher split. STF 1338 is a tight mag. 6.5 & 7 pair.

I could not split them at x133 and at x266 they were split for periods of good seeing. I had the PA as 270 and the separation as 1” (WDS 290/1.1). The colour I noted as off-white. This is a binary of 300 years so will show change over time.) – previous observation


The Moon had cleared the tree by this time and I moved the scope to observe, I was disappointed to see that Gassendi A was not in a high contrast position. This had happened the night before when it was raining very heavily.

I took several images with my A607 camera and these are in the lunar forum. The Images covered Gassendi, Oceanus Procellarum and Tycho. I tried to get closer to the Valles Schoteri but the seeing was still well below average so I decided to call it a night.



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