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Zip file Earth Rotation (PowerPoint multimedia presentation)
(19 MB) (Requires a PowerPoint Viewer)*
more information
PDF file Deconstruction of DIY, mechanical, Moon-Phase calculator
(382 KB) (Requires a PDF Viewer)*
more information
PDF file Time-and-Tide Clocks: How they work, setting them up and keeping them accurate
(163 KB) (Requires a PDF Viewer)*
more information

 

 

Videos

The videos below are best viewed in HD resolution and in full-screen mode.
After you start the video, the player controls

will appear at the bottom of the player panel.
Use those controls to immediately pause the video, then, in "settings," select the highest available quality and then click on the "Full Screen" button.


 

Weekday Names and Planetary Hours

How is the 7-day week rooted in astronomy and where do the names of our weekdays and their order come from?
Music is from Gustav Holst's "The Planets" (Venus and part of Saturn).


 

Day: Solar vs Sidereal

This is a reworking of Michael Zingale's animation showing why the interval between successive noons (the solar day) is about 4 minutes longer than the Earth's true rotation period (the sidereal day).

Michael's astronomy animations are done in Python, then assembled into movie files, but the movie version of this animation on his site has some graphical elements missing from it, whose absence makes it less visually obvious what the animation is showing. I have corrected that omission in this version by adding the Earth-Sun line at the two noon positions, where the observer's meridian (indicated by the black dot) is on that line.


 

Phases of the Moon - Southern Hemisphere

This is a video response to YouTube video Phases of the Moon 3D animation showing the phases as seen in the Southern Hemisphere. The Moon is oriented as seen from (roughly) the latitude of Canberra, Australia. (It was created from the above video, but with the Moon's disc rotated 180.)


 

Time Zones and the International Date Line

Travel through time, watching the changes, hour by hour, in the standard times of all 24 time zones at once, and learn how the International Date Line works.

At tiny.cc/timeanddate you can download the original PowerPoint Show this video was made from. (See the section headed Part 2.)

This is a video response to Shepdi's YouTube video How the International Date Line Works. I made this to correct a minor inaccuracy in Shepdi's video. Shepdi's error is as follows:

At 0:21 it says that when it's 23:00 to 23:59 at the Date Line, the entire world is on the same day. That is not so. Time Zone 12 is bisected by longitude 180. New Zealand is in its western half (+12) and Baker Island (011.5'N, 17628.5'W) is in its eastern half (-12). At Mon, 11:30 UTC, it is Mon 23:30 in NZ, but in Baker Island it is Sun 23:30. Most places geographically within zone -12 keep the time (or at least the date) of one of their neighbouring zones, but a few do keep day & time at UTC-12.

So during the hour Mon 11:00 to 12:00 UTC, it is Monday everywhere except in Zone -12, where it is still the last hour (23:00 to 23:59) of Sunday. AND something similar is also true in the next hour, when it is Monday everywhere except in zone +12, where it is the first hour (00:00 to 01:00) of Tuesday. Note also, that, unlike the impression conveyed at 0:30 in Shepdi's video, when it is midnight at the Date Line, it is midnight throughout time zone 12, which straddles the Date Line.

 

 


 

 

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All files on this site are copyright. You may use them as you wish for personal, non-commercial purposes, but unless you have received permission from me to do so, please do not put copies of these files on any other website or otherwise directly redistribute them, either electronically or in hard copy form. To make them available to others, please link to this website (using the following address) or provide others the web address, which is: http://tiny.cc/astronomy/