Clear Sky Chart and Observational Wx for:
S o u t h A r l i n g t o n / M a n s f i e l d , T X
Clear Sky Chart   Hourly Point Forecast


Calculate Focuser Hole Placement (Web-Based Javascript Form)
This is a Javascript, web-based form to figure focuser hole placement on a newtonian telescope tube based on size of tube and mirror focal ratio.
Focuser Hole Placement
Telescope/Eyepiece Calculator (Web-Based Javascript Form)
This is a Javascript, web-based form to figure the optical qualities of a reflecting newtonian telescope itself and any eyepieces you may use on it. Has fields to enter telescope measurements and eyepiece measurements. Shows resolution, Dawes Limit, Min/Max eyepiece recommended for your telescope, Longest eyepiece recommended for your eye's entrance/exit pupil, and several more.
Calculate Your Entrance Pupil (Web-Based Javascript Form)
This page describes how to use the template file provided to find the ENTRANCE PUPIL diameter of your own eye. This is useful in determining the highest power eyepiece to use on your telescope (See my telescope calculator to figure telescope/eyepiece exit pupil).
Magnetic Declination Calculator (External Website)
Calculates the compass offset of your location. This allows you to point your telescope to TRUE north using a magnetic compass. Simply point your compass at magnetic north and then offset it by the amount this calculator shows you. Based on your Latitude/Longitude and is from the Geological Survey of Canada (the Canadian equivalent of the US Geological Survey).
Degrees, Minutes, Seconds
and Decimal Degrees Latitude/Longitude Conversions
(External Website)
Convert Latitude/Longitude from DD:HH:SS to Decimal format and back with this calculator. Useful for different software and spread sheets which often will require you to enter your Lat/Long but often one uses one format and other use the other format. This will give you the ability to convert back and forth.
Cross Staff - Angular Separation Calculator (Web-Based Javascript Form) NEW!

This is a Javascript, web-based form to figure the angular separation of objects using a 16th century Cross Staff such as used by Tycho Brahe and other pre-telescopic astronomers. This is used to teach angular separation and celestial divisions of the sky to young or novice amateur astronomers.

This form goes with the Cross Staff build instructions using a standard $0.68 yardstick from Home Depot and an observing assignment sheet found here, to teach how Cross Staffs were used.

This all leads into teaching how to use your hands as the cross staff to gauge distances in the sky (something handy to know when learning your way around star charts).

Dewpoint Calculator (Web-Based Javascript Form) NEW!

This is a simple Javascript, web-based form to figure the dewpoint from the ambient temperature and the relative humidity.

This form can help determine when your optiocs will start to fog up and condensation occurs.

Radial Velocity (MPH) at a Given Latitude on Earth - Calculator (Web-Based Javascript Form) NEW!

This is a simple Javascript, web-based form to figure your radial speed on the surface of the earth at any given latitude.

This is a for-fun calculation because it assumes the earth is a perfect sphere (it's not) and also that the surface is smooth (it's not). Therefore all speeds are approximations.

click on image to learn more
Make a Star Clock! (External Website)
Use the stars to tell what time it is with surprising accuracy. Any time of the night, any time of the year. Print this clock from the attached PDF file (Star+Clock.PDF) and create your own Star Clock.
Big Dipper Star Clock
Make a Planisphere! (External Website)
Make your own star chart (Planisphere) that will show you the night sky for your location at any time of the year. Follow the instructions found on the linked page and you will have a great tool for learning and navigating the night sky.
Star Chart
Make Your Own Sundial! (External Website)
Creat your own sundial from paper, cardboard and pencils to tell time from the Sun.
Paper Sundial;


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