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.

Source
- 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)

 From ICEINSPACE
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

#FSstarparty

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


#FSstarparty
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.

Tuesday, 3 May 2016

3rd Free State Star Party



Photo: Frans Human (ASSA Bloemfontein)
A Stary Party in the warm heart of Central South Africa
3 - 5  June 2016 (Friday - Sunday)
Where
On the farm Gansvlei close to Brandfort (13km)
GPS Coordinates:  28°47'48.63"S   26°28'25.66"E
Gansvlei Information (Pdf) Booking via Shaun Staats  -   assabfn@gmail.com

GPS Coordinates  28°47'48.63"S   26°28'25.66"E
 Google Earth - Gansvlei - FS Star Party

Observation site
Storage room close to observing site during night/day.
Separate astro photography site available not to disturb serious observers.
Electricity available for telescope and electronic equipment (No kettles or heaters).
Observers must bring their own leads to get power from a central point in the veld.
Bring covers if you want to leave your equipment in the veld during the day.
 

- Have respect for your fellow observers. Use your headlight sparingly. You are blinding someone next to you. No bright white/red lights when observing starts. 

Deep-sky Marathon
ASSA Bloemfontein did the  first Deep-sky Marathon on Gansvlei in 2014 . (ASSA Top-100 Observing List). It is based on the very popular Messier Marathon. It was customized for deep sky objects visible in Southern-Africa.


 Visit the ASSA Marathon web page Sections – Deep-sky Section > Nebulae >  Clusters >
- Deep-Sky Marathons

The FS Star Party is not about marathons alone. It is also an event where astro friends will do some serious observing, astro photography and relax with hot coffee and serious braaiing. 


Weather
Extreme – In 2014 we measured - 7°C during the first night. Prepare with warm clothing and bedding. In 201 5 dew caused havoc. Bring your dew heaters. Come prepared!

Meals
Bring your own food according to your dietary preferences.
Hot beverages will be available during the night at a Coffee point
Central braai area available. We braai early to be ready for the nights observing.
Brandfort - 13 km
- Branfort Slaghuis/Butchery is the place to buy your meat   (
14 Voortrekker St, Brandfort)

Bloemfontein 52 km

Provisional Programme

Friday  –  3 June 2016
Morning/Afternoon: Arriving and setting up at observing point
Evening - Early Morning:  Observing

Saturday
–  4 June 2016
Morning: Visit Brandfort or sleep late; (No official programme)

Evening - Early Morning:  Observing

Sunday –  5 June 2016
Breakfast and we all leave! 

General
 

Cost (2016)
1. Registration fee – R100 p/p
 

2. Accommodation costs

Per night Tariff:
R100 per person per night. Include bed, hot shower, kitchen

Camp in own tent:
R80 per person per night.  Include bed, hot shower, kitchen (Bring your own bedding. It is deep winter – be prepared.

- Wood for barbeque (Saturday afternoon) available.

- Venue avaiulable for Friday and Saturday night (3/4 June)

 

Cash payment on arrival.
Contact Shaun Staats – via assabfn@gmail.com   


To book
Cut and paste the info below and email your information to assabfn@gmail.com  
 

Name / Surname:
ASSA Centre / Other:
Number of people:
Email:
Cell no:
Bed in Room  (Number):          (No single/double Rooms available)
Camp site:


Other accommodation
 Various  
  Ou Pastorie 
  Lekkeslaap – Near Brandfort

June is Deepsky Marathon Month at the Free State Star Party - Helpful links

Saturday, 30 January 2016

Six naked-eye planets



In the last week of January and into the first week of February, all six naked-eye planets - Mercury, Venus, Mars, Jupiter, Saturn, and the Earth - will be visible at the same time.

In the last week of January and into the first week of February, all six naked-eye planets - Mercury, Venus, Mars, Jupiter, Saturn, and the Earth - will be visible at the same time.
Starting late-January, in the morning sky shortly before sunrise, six planets will be visible at the same time. The trickiest planet to catch will be Mercury, which - as the planet nearest the Sun and thus never moving too far from our bright star - will be low in the east before sunrise.
Start looking on the morning of January 23, when super-low Mercury may be visible before sunrise. It gets easier each morning afterwards.
From January 26 to about February 07, the Moon joins the sextet, waning to a beautiful slender crescent on February 06, when it makes a spectacular grouping with Venus and Mercury - this is not to be missed!