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Observing Session 29/08/06

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lunator

lunator

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Here is my observing session from a couple of days ago.

I have included a brief outline of my observing method.

The night was clear and the seeing was good. It was probably the

best night this Summer.

I knew the seeing was good as I split alpha Herc in the 18mm eyepiece(x67). I had never done that before and as the stars were only just split the companion did look really green against the bright yellow/orange of the primary. Usually it takes the 12.5 mm to split htis pair and the separation makes the colour contrast less apparent. If you have an RFT I would try and get this pair just spilt. It is worth it. :laugh:

Here is my observing method

I have settled into an observing pattern where I usually take about

20-30 minutes per observation split roughly between the sketching

and observation notes and the actual measurments.

My method is as follows. I have Cartes du Ciel open on my laptop.

Once I have located the pair I observe them with the 18mm

orthoscopic eyepiece I note the general field, any interesting

asterisms and the star colours if apparent. I do not always put the

pair at the centre at this point as a try to find the 'richest' view

which may mean that the pair I am mesuring are well off to one side.

I re-centre the pair and measure using the 12.5 MG & 3x Barlow.

Below is the Observing report.

Rgds

Ian

Observation Report 29/08/06

Target. STF 2096

Date: 29/08/06 Time: 20:35 UT

Seeing: 3/5 Transparency: 4/5

Site: London/Suburban - Lat: 51:27:54N (51.4651) Lon: 0:16:36W (-

0.2767)

Site classification: Suburban ZLM: Mag4.5

Sky Condition: Clear Moon: Not risen

Telescope: Orion Optics 200mm F6 Eyepiece: 18mm Ortho

Magnification: x67 Barlow: No

Comments: Wide easy pair, sprinkling of faint stars too many to draw

Primary Colour: Yellow

Secondary Colour: Orange

General Notes: Wide easy pair in 18mm.

Measurements: PA: 88 Sep: 22.3"

(3x Barlow & 12.5mm MG. scale constant 5.3" per division)

Target. STF 2086

Date: 29/08/06 Time: 21.05 UT

Seeing: 3/5 Transparency: 4/5

Site: London/Suburban - Lat: 51:27:54N (51.4651) Lon: 0:16:36W (-

0.2767)

Site classification: Suburban ZLM: Mag 4.5

Sky Condition: Clear Moon: Not Risen

Telescope: Orion Optics 200mm F6 Eyepiece: 18mm Ortho

Magnification: x67 Barlow: No

Comments: Moderately rich field. Stars of similar magnitudes make up

3 distinct triangles

Primary Colour: Cream Secondary Colour: White

General Notes: Easily split in 18mm

Measurements: PA: 157 Sep: 13.3"

(3x Barlow & 12.5mm MG. scale constant 5.3" per division)

Target. STF 2118

Date: 29/08/06

Time: 21:35 UT

Seeing: 3/5

Transparency: 4/5

Site: London/Suburban - Lat: 51:27:54N (51.4651) Lon: 0:16:36W (-

0.2767)

Site classification: Suburban

ZLM: Mag 4.5

Sky Condition: Clear

Moon: Not Risen

Telescope: Orion Optics 200mm F6

Eyepiece: 9mm Ortho

Magnification: x233

Barlow: Yes

Comments: Tight pair, split when seeing was good

Primary Colour: Cream

Secondary Colour: Cream

General Notes: Tighest pair measured to date. Difficult to judge PA

accurately.

Measurements: PA: 74 Sep: 1.1"

(3x Barlow & 12.5mm MG. scale constant 5.3" per division)

Target. STF 2098

Date: 29/08/06: 22:00 UT

Seeing: 3/5

Transparency: 45

Site: London/Suburban - Lat: 51:27:54N (51.4651) Lon: 0:16:36W (-

0.2767)

Site classification: Suburban

ZLM: Mag 4.5

Sky condition: Clear

Moon: Not Risen

Telescope: Orion Optics 200mm F6

Eyepiece: 18mm Ortho

Magnification: x67

Barlow: No

Comments: Moderately rich field

Primary Colour: White

Secondary Colour: Orange

General Notes: Easy split in 18mm and a clear colour contrast

Measurements: PA: 147 Sep: 14.3

(3x Barlow & 12.5mm MG. scale constant 5.3" per division)

Target. STF 2095

Date: 29/08/06: 22:20UT

Seeing: 3/5

Transparency: 4/5

Site: London/Suburban - Lat: 51:27:54N (51.4651) Lon: 0:16:36W (-

0.2767)

Site classification: Suburban

ZLM: Mag 4.5

Sky condition: Clear

Moon: Not Risen

Telescope: Orion Optics 200mm F6

Eyepiece: 9mm Ortho

Magnification: x133

Barlow: No

Comments: Squashed trapezium of stars to the West

Primary Colour: White

Secondary Colour: none noted

General Notes: clear split in 9mm, elongation in 18mm

Measurements: PA: 161 Sep: 5.3"

(3x Barlow & 12.5mm MG. scale constant 5.3" per division)

post-12723-133877321874_thumb.jpg

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lunator

lunator

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WH

The orthoscopic eyepiece is the best for double star work.

It has very few elements so the light loss is minimal & ther are no internal reflections.

The FOV is flat what you see is what is there and where it should be.

The main 'drawback' with Orthoscopic eyepieces is a narrow FOV but for DS work this is irrelevant as most of the pairs you'll look at are between 50 & 0.5".

A good plossl will perform close to an orthoscopic but the benfit of a wider FOV is offset by a curvature of the field near the edges.

Cheers

Ian

P.S.

If you have an eyepiece that gives you betwwen 70-90x mag I would be intrested to know what colours you see Alpha Herc.

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