Eclipse 01 Preview

Introduction

Eclipse01 is based around 5 screens, which show eclipse data from different perspectives and user needs. The 5 screens are

Eclipse Circumstances
Current Circumstances
Centre Line Nav
Countdown Clocks
Current Time

Eclipse Circumstances

The focus of this screen is on the circumstances of the eclipse from the observing site. The computer calculates the times of the eclipse contacts, the eclipse duration, and the direction and speed of the shadow, amongst other things.

The fields on this screen are :-

Lat:	The latitude of the observing site - either entered manually, or read from a GPS receiver
Lon:	The longitude of the observing site
Alt:	The altitude of the observing site
Duration:	The duration of the total eclipse (not shown in the screenshot)
Magnitude:	The magnitude (i.e. fraction of the sun's diameter covered by the moon) of the eclipse at mid eclipse
Moon/Sun:	The ratio of the size of the moon to the size of the sun
Moving @	The direction that the moon's shadow is moving (not shown in the screenshot)
Speed:	The speed of the moon's shadow at mid-eclipse (not shown in the screenshot)
Dist:	The distance to the nearest point on the centre (not shown in the screenshot)
Event Clock	A count down/up timer to the event in question
Event Time	The time (local time) of the event in question
P	The position angle of the event from the north point on the sun measured eastward
V^o	The position angle of the event from the zenith ("top") point on the sun measured counter-clockwise
Vh	The position angle of the event in "clock hours"
Alt	The altitude of the event above the local horizon
Azi	The azimuth (0 = North, 90 = East) of the event
Limb	The lunar limb correction that was applied to the event time (only for C2 and C3 - not shown in the screenshot)
C1:	First Contact - the start of the partial eclipse
C2:	Second Contact - the start of the total eclipse
Mid:	Mid Eclipse
C3:	Third Contact - the end of the total eclipse
C4:	Fourth Contact - the end of the partial eclipse
[GPS NMEA] [KEEP ON] ...	Status line

Current Circumstances

The Current Circumstances screen deals with the eclipse as it appears at this moment to the observer. Note that the screenshot above has a bit of blank space towards the bottom-right. I intend to put a small graphic in that area showing the view of the eclipse.

The fields on this screen are :-

Lat:	The latitude of the observing site - either entered manually, or read from a GPS receiver
Lon:	The longitude of the observing site
Alt:	The altitude of the observing site
Magnitude:	The magnitude (i.e. fraction of the sun's diameter covered by the moon) of the eclipse
Moon/Sun:	The ratio of the size of the moon to the size of the sun
P:	The position angle of the moon from the north point on the sun measured eastward
V^o:	The position angle of the moon from the zenith ("top") point on the sun measured counter-clockwise
Vh:	The position angle of the moon in "clock hours"
Alt:	The altitude of the eclipse above the local horizon
Azi:	The azimuth (0 = North, 90 = East) of the eclipse
Coverage:	The percentage of the area of the sun covered by the moon
Dist:	The distance to the centre of the moon's shadow.
Dirn:	The direction to the centre of the moon's shadow.
Speed:	The current speed of the moon's shadow.
Local:	The current local time
UTC:	The current UTC time (commonly called "Greenwich Mean Time")
[GPS NMEA] [KEEP ON] ...	Status line

Center Line Nav

The Centre Line Nav screen is concerned with getting the observer to the centre line! Not shown in the screenshot is the "Compass" that will point the way to the nearest point on the centre line. This screen requires the use of a GPS satellite navigation system.

The fields on this screen are :-

Lat:	The latitude of the observer - as read from the GPS receiver
Lon:	The longitude of the observer
Alt:	The altitude of the observer
km @	The distance and direction to the nearest point on the centre line
Nom. Duration:	The nominal duration of totality on the nearest point on the centre line
Approx Duration:	The approx duration of totality at this point
[GPS NMEA] [KEEP ON] ...	Status line

Countdown Clocks

This screen shows a large clock (on the left-hand side) counting down to the next eclipse event. On the right-hand side, there are smaller clocks that count up/down from/to second contact (top), mid eclipse (middle), and third contact (bottom). I intend to have an option ("Auto Screen") which will force this screen to pop up (say) one minute before second contact and stay there until (say) one minute after third contact. There will also be an option ("Auto Light") which will force the Psion backlight to come on for this period!

I will also program the Psion to beep at you when an event is imminent. I'm even thinking about the possibility of making the Psion give voice announcements! It should be possible - the major issue is that the Psion is not a fast computer (!), and tends to struggle with too many things to do at once.

Current Time

All of the features for using this program on the field on eclipse day depend on accurately knowing the time. This clock will allow you to monitor the Psion's clock (from a distance, even!) and also provide a time signal to other eclipse observers (assuming that you are properly synchronised). I have it in the back of my mind to synchronise the Psion's clock to the GPS clock - however, no manufaturers of consumer-grade GPS equipment give enough priority to a GPS's capability to deliver accurate time.

Future Developments

There are three obvious things missing from this program - the ability to display the latitude and longitude of the centre line, limits etc; the fact that the program is limited to one eclipse only; and the ability to draw (even rudimentary) maps. Watch this space! However, my priority is getting something good working for the eclipse on 21 June 2001

Last Updated: 14 Sep 2000