Date and Time

The default date shown is always the Gregorian date. Even if the date is earlier than 1582, the Gregorian date is still the default date, but the Julian date will be shown alongside. Therefore, if correlating to dates in the Julian era from 45 BCE to 1582, then you need to aware that you have two dates to choose from.

Be aware that other software may automatically flip to the Julian Calendar for dates earlier than 4-Oct-1582, so if comparing results and you see a sudden date difference before 1582, then that is the reason. The Julian and Gregorian calendars become aligned at around the year 250 CE, then drift apart again.

Note that the BCE/CE or BC/AD representation of dates does not include the year zero. Therefore, the BCE representation of a date is one year different from the negative year number.

The Julian Day Number 0 occurs on 01/01/-4712 (or 01-Jan-4713 BCE) in the Julian Calendar, which is also 24/11/-4713 (or 24-Nov-4714 BCE) in the Gregorian calendar.


Time Zones

Time Zones have only existed in their current form for about the last 100 years. Prior to that they were something approximately similar to what they are today. Additionally, some countries have daylight savings and some don’t. The date for changing to daylight savings varies, and some countries have had daylight a one point and now don’t, or vice versa. This all leads to problems when trying to correlate historical dates.

Some examples of complexities of historical time zones follow.

Thailand is a simple example. Currently it is at +7:00 UTC. Prior to 1920 it was at 6:42:04 UTC

Western Australia is slightly more complex. Currently it is as +8:00 UTC and does not have daylight savings time. It had trial periods of daylight savings from 1974-75, 1983-84, 1991-92 and 2006-09. Then prior to 1895 it was at 07:43:24 UTC

England is currently at 0:00 for winter time , 01:00 for summertime. But prior to 1847 was at -0:01:15

Within the SkyView, there are two possibilities for Time Zones that can be selected in the parameters form.

  • Assume all times in the past and present have the same time-zone definition as of the current time (today). This is probably the least confusing option.
  • Use the correct historical time-zones. This will give the correct historical times for a particular year at that location, but the time values shown may appear erratic.

As an exercise, you can select one of the locations listed above, and notice how the time and time-zones vary as you select some historical dates, and or winter and summer months.


Other Calendars.

Computations for the Hebrew and Islamic calendars have been introduced. Both these calendars are “lunar calendars”, meaning they follow the moons cycle. They both should be showing the beginning of the month just after a new moon. This is generally the case, but there may be some slight drift after 1000 years or more. These can be allowed or disallowed from the parameters form, as required.


More details on selecting the Observer Location

Clicking the "Enable Edit UTM" will allow to change the WGS84 UTM values, and allowing for the Lat-Long to be computed from the UTM. To revert back, simply click "Enable Edit Lat-Long".

The map displayed is from the Microsoft Bing Maps API. An internet connection is required to view the map.

The time zone is determined from the selected location, which returns the time zone value for either standard time or summer time (DST) depending on the time of the year. The input information are the latitude and longitude of the selected location. If a location is selected over the ocean, a time zone value computed from a 15 deg segment of longitude is returned. 

The location data can be saved to the local computer, which will be automatically re-loaded when the app is next restarted. To save a current location setting, click on "Add currett location to list". To restore a location, just click on it. When right clicking on a location, a drop-down menu will appear which gives options for removing and renaming the saved location.


Keys for the Bing Maps API

The map displayed is from the Microsoft Bing Maps API. This API requires an active internet connection, so if no internet connection is available then the map does not display or update. Additionally, an API key is required for it to function and a temporary key is embedded in the software.

It is possible that at some time in the future, the Bing Maps API key that is embedded in the software will cease to work, either due to expiration or over-use. You will see a message on the map saying "Invalid Credentials. Sign up for a developer account".

In that situation, you can obtain your own key from and load it from the option under the Tools menu. Use your regular Microsoft username and password.

This new personal key may become disconnected from SkyView software when you re-install or update SkyView, so will need to be entered again the SkyView Tools menu.

As far as I know, for fairly limited use, the Bing Maps key is free use up to a certain number of daily transactions (which is quite high), even though it is called a "billable key".  Although I dont believe there is any extra cost associated with getting a Bing Maps API key for low level usage, but if there is any extra cost, then this is extra and above any cost that may have been paid to acquire the SkyView app.

When obtaining a key, select Key Type=Basic and Application Type=Public Windows App (8.x and earlier). The Application Name is SkyView.