Thursday, 1 September 2016

Partial eclipse of the Sun in South Africa - Thursday, 1 September 2016

Today, sky watchers in more than 50 African countries witnessed a solar eclipse. On Thursday, 1 |September 2016, the new Moon passed in front of the sun, covering as much as 97% of the solar disk. This is how the sun looked from Bloemfontein, Free state, South Africa at almost maximum partial eclipse.

Visible sunspots are 2581 (left) 2585 (right).

Photographer: Hannes Pieterse
A single image trough an Celestron 11GPS telescope and F/6.3 reducer with Astro solar filter (ND 3.8)
Camera: Canon 40D
Exposure Time: 1/2000
ISO: 400
Date Taken: 2016:09:01 10:55:34
Conditions: Mild Cloud cover.

 Links to the Solar Eclipse (1 September 2016)

Sunday, 28 August 2016

Eclipse of the Sun visible in South Africa

What will I see?

A solar eclipse is a rare opportunity to see the solar system in action.

For a short time, the Moon will pass between us and the Sun, and instead of seeing the Sun as a round disc, it will have a “bite” out of it. This “bite” is the Moon, and the size of the “bite” changes as the Moon slowly moves along. 

Wednesday, 6 July 2016

1.5.3 Measuring the field of view (Plan your Observing)

Click on image  to Enlarge (Source: NASA - Chandra X-Ray Observatory )

The simplest method of measuring the field of view relies on the use of a star chart.

Knowing north and east in the sky, you can easily turn your star chart so that the image in the eyepiece corresponds to the chart. Look for two stars that just fit in your field of view, and locate these stars on the star chart. You can now measure this distance on the map and compare it with the scale on the margin of the map to convert your linear measurement to degrees or arc minutes.

Remember that 1 degree (°) = 60 arc minutes (60′) = 3600 arc seconds (3600″). Binoculars typically have fields larger than 4degrees , and telescopes normally give a view smaller than 2degrees.

It is essential to be able to judge angular distances in the sky. The following table lists some angular estimates:

Solar / lunar diameter: ½°
Width of index nail at arms length: 1°
Orion’s Belt: 3°
Short arm of Crux: 4½°
Long arm of Crux: 6°
Width of clenched fist at arm’s length: 10°
Long arm of Diamond Cross: 10°

   Everyday objects can also serve as angular gauges. To determine the apparent angular size of anything in degrees, divide its linear width by its distance from your eye, then multiply by 57. For example, a 30cm ruler held one metre from your eye measures 30 ÷ 100 x 57 = 17°.
   A more accurate method to determine the diameter of your field of view involves measuring the time it takes for a star to drift across your field along the east-west line.
   This method is only useful for telescopes, since a star will take ages to cross the large field offered by binoculars. Choose any bright star, preferably far from the south pole – a star in Orion’s belt would be a good choice.
   Centre the star in your field of view, turn off the drive, and place the star just outside the eastern edge of the field. As the star drifts into view, start your stop-watch. When the star dis appears at the western edge, stop the watch and note down the elapsed time. Repeat this measurement several times and take the average.
   If this average time, T, is measured in minutes, then: field of view in arc minutes = 15 x T x cosine( D ), where D is the declination of the star (taken from a star catalogue, or estimated from a starmap).
   For example, suppose you measure several transits of Canopus and calculate the average time to be 3.5 minutes. Canopus’ declination is roughly –52.7°. The field of view is then 15 x 3.5 x cos(–52.7) = 15 x 3.5 x 0.6 = 31.5 arc minutes. Thus the field of view is roughly half a degree across.
   Make a note of the size of each eyepiece in your logbook, since a given eyepiece used on a specific telescope has a fixed field of view.

- Download - Deepsky Observer's Companion (Pdf)
Deepsky Observer’s Companion (P 13)
Auke Slotegraaf
Director: Deepsky Observing Section,
Astronomical Society of Southern Africa

Saturday, 18 June 2016

A little red dot....

Skytools 3 view of the carbon star, DY Cru (feint red dot) with 10" Dobsonian and 10mm eyepiece.
DY Cru. The little red dot that could!

At the 2016 Free State Star Party  Johan Smit  (ASSA Pretoria)  "exposed" us to a feint red dot in the constellation of Crux.

 Most observers use beta Crucis as a beacon  to find nearby NGC 4755, the ‘Jewel Box’ (Kappa Crucis Cluster, NGC 4755, Caldwell 94).

Therefore we miss out on this ruby of the 9th magnitude carbon star within its glow. Nicknamed 'Ruby Crucis. (aka DY Cru, NSV 19481, CCCS 2031, EsB 365)

little red star near beta crux
"Ok, given up trying to find the name of the star. It is a little red star near beta crux. You can;t see it with the nude eye but through my 8" Dob it is there. You don;t really notice it unless you are looking for it but in a 12.5mm EP it should be in the same FOV as beta crux. I hope one of you knows which this is."

Go and find it...

Links to explore this little red gem and other carbon stars

Sunday, 5 June 2016

Wednesday, 1 June 2016

Part 2 of my "How dew you dew" action for the Free State Star Party 3 - 5 June 2016


How to fight the dew from the top?  Start a fan club.

Will it work? Maybe to much vibration?  Will find out soon.

Heatwaves in the tube? Is "bad seeing" not better than "no seeing" at all? 

 It is a small 60mm fan right behind the secondary mirror. I plan to add an on/off switch and a variable resistor to bring down the speed or turn it off if there is to much vibration.

Dew on the secondary mirror was a bigger problem then dew on the primary mirror,  during the previous star party (2015).

And the white wiring?  That is a nichrome heater (harvested from an old electric blanket)  to heat up the air a wee bit. Maybe some airflow (fan) will do the trick.

* Plan B is to  mount the fan on the edge of the scope tube and point it in the direction of the secondary mirror. What next?

Some links with more ideas

Tuesday, 31 May 2016

Part 1 of my "How dew you dew" action for the Free State Star Party 3 - 5 June 2016

Dealing with dew at the Free State Star Party.
Maybe it will help. Some amateur astronomers are skeptical (3rd link). Maybe  a disk at the back to force more air onto the mirror as suggested by the author..

 Will use the fan  in combination  with heater made from nichrome wire (old electric blanket).
- Eyepiece area
- Secondary mirror

I will give feedback after the weekend.

Hannes Pieterse

Some links to helpfull web sites:
Using fans with Newtonian telescopes

Attaching a Cooling Fan to Newtonian Telescope

A simple telescope fan installation

Monday, 9 May 2016

Transit of Mercury - Boyden Observatory - Bloemfontein, 9 May 2016

Photo: Hannes Pieterse

Students  from the Department of
Physics from the University of the Free State watch the Mercury transit projected by the 20 cm Coelostat (Solar Telescope)  at Boyden Observatory, Bloemfontein, South Africa.

Sunspots AR 2542 and 2543 are clearly visible on the gallery images without cloud interference.