Starry Night Manual (Time)

Time

Another important consideration in determining what can be seen in the sky is the time of the observation. If you look up at the beginning of the evening and again at midnight, you will have seen that the stars have shifted their position. What you are seeing is the effect of the Earth rotating on its axis. This movement of the sky is the most obvious effect of the passage of time, but there are many more subtle and interesting effects to be observed that can only be seen over longer periods of time.

This section will teach you how to use the tools and commands for changing and manipulating time. It is with these features that Starry Night offers the most power and promise for learning. Many significant celestial events occur over very long periods of time, making them difficult to observe. Through the use of the Time tools, Starry Night can compress hundreds or thousands of years worth of change into a few minutes' duration, and in doing so, makes these movements easier to see, and easier to comprehend.

The Current Time

By default, Starry Night opens new windows at the current time (the time your computer is set to). Your window's current time is always shown beside the little clock icon at the bottom of all open windows. In the example below, your current time is 6:26:39 PM, on September 14th, 1996. The symbol between the date and time indicates the window's time flow, which can be set by the Time Palette. (A small square indicates that time is stopped, a right pointing triangle indicates time is going forward, and a left pointing triangle indicates that time is going backwards.)

The view Starry Night displays in the window will automatically update as time passes. By default the view is updated every 5 seconds on most computers (on older Macintoshes the default is 30 seconds). This value is adjustable, and can be changed in Preferences under the Settings menu.

The Time Palette

This palette is used to display, set and control time. To see the Time Palette, select Time from the Window menu or use the Time button located on the Tool Palette. Adjustments can be made to the time by using the VCR-like controls of the Time Palette.

Stop

To freeze time at its current point, press the Stop button.

Realtime

Clicking the Realtime button sets the current window's time flowing at a normal rate.

Forward and Back

Pressing the Forward button to watch the sky advance in time steps (see below). Pressing the Flow Back button reverses time.

Single Step

Pressing the Single Step buttons will advance the current view one time step, backward or forward, depending on the button clicked.

Current Time Display

The right hand side of the Time Palette displays the current view's time. To change the time, click on the element you wish changed and then type a new value. For instance to change the year, click on top of the year (it will become selected) and type "2001" to change to the year 2001. You can also adjust the time using the little increment buttons that appear whenever a unit or number is selected.

Keyboard shortcut: Click on part of the current time or date to highlight it. Use the keyboard's "+" and "-" keys to change the value up or down by one unit at a time. You can also use the tab key to switch between the different elements.

System Time

Clicking the System Time button (the one with the icon of a computer screen) will show you what the sky looks like from your current location right now, i.e.: the time on your computer. For example, if you've been adjusting the time but now wish to see the sky as it looks at this moment, pressing this button will reset the current view's time.

Note: If your current view's location is in a different time zone than your default setting, Starry Night will automatically adjust the time to your new location's local time. If your current location is in space or on another planet, the time is set to Universal Time, the astronomical standard based on the time at Greenwich, England.

Time Step

The speed at which time flows is adjusted by the Time Step. Initially this is set to be three minutes but this can be changed to any setting you like. To adjust the time step's number, select the number and use the little increment buttons to raise or lower the number's value. You may also use the keyboard's "+" and "-" keys, or simply type in the number you wish.

By default, the time step's unit is set to "minutes", but this can be switched to seconds, hours, days, sidereal days, lunar months, sidereal months, or years. To adjust the time step's unit, click the unit, then use the up/down mini buttons to raise or lower its value. You may also type in the first letter of the unit you wish to change to. (Type "m" for minutes, "s" for seconds, "h" for hours, "l" for lunar month, and "t" for sidereal month).

Daylight Savings Time

You may adjust the time to reflect Daylight Savings Time (if it applies to the current viewing situation) by clicking on the small Sun icon to the left of the time display. Starry Night uses this information to calculate universal time. When daylight savings is on, the Sun icon will light up in yellow.

To set Daylight Savings Time for your Home Location see Setting Your Home Location in the Getting Started Chapter.

Setting Julian Dates

The Julian Date represents the number of days that have elapsed since January 1, 4713 BC. Astronomers sometimes use Julian dates in order to avoid the problems resulting from historical calendar changes. To see the current time expressed as a Julian date, click the Julian button to open the Julian Time window. If you'd like to set the current time to a specific Julian date, type in the Julian date you wish to view, then click the Set Time button.

		Another important consideration in determining what can be seen in the sky is the time of the observation. If you look up at the beginning of the evening and again at midnight, you will have seen that the stars have shifted their position. What you are seeing is the effect of the Earth rotating on its axis. This movement of the sky is the most obvious effect of the passage of time, but there are many more subtle and interesting effects to be observed that can only be seen over longer periods of time. This section will teach you how to use the tools and commands for changing and manipulating time. It is with these features that Starry Night offers the most power and promise for learning. Many significant celestial events occur over very long periods of time, making them difficult to observe. Through the use of the Time tools, Starry Night can compress hundreds or thousands of years worth of change into a few minutes' duration, and in doing so, makes these movements easier to see, and easier to comprehend. The Current Time By default, Starry Night opens new windows at the current time (the time your computer is set to). Your window's current time is always shown beside the little clock icon at the bottom of all open windows. In the example below, your current time is 6:26:39 PM, on September 14th, 1996. The symbol between the date and time indicates the window's time flow, which can be set by the Time Palette. (A small square indicates that time is stopped, a right pointing triangle indicates time is going forward, and a left pointing triangle indicates that time is going backwards.) The view Starry Night displays in the window will automatically update as time passes. By default the view is updated every 5 seconds on most computers (on older Macintoshes the default is 30 seconds). This value is adjustable, and can be changed in Preferences under the Settings menu. The Time Palette This palette is used to display, set and control time. To see the Time Palette, select Time from the Window menu or use the Time button located on the Tool Palette. Adjustments can be made to the time by using the VCR-like controls of the Time Palette. Stop To freeze time at its current point, press the Stop button. Realtime
		Clicking the Realtime button sets the current window's time flowing at a normal rate. Forward and Back Pressing the Forward button to watch the sky advance in time steps (see below). Pressing the Flow Back button reverses time. Single Step
		Pressing the Single Step buttons will advance the current view one time step, backward or forward, depending on the button clicked. Current Time Display
		The right hand side of the Time Palette displays the current view's time. To change the time, click on the element you wish changed and then type a new value. For instance to change the year, click on top of the year (it will become selected) and type "2001" to change to the year 2001. You can also adjust the time using the little increment buttons that appear whenever a unit or number is selected. Keyboard shortcut: Click on part of the current time or date to highlight it. Use the keyboard's "+" and "-" keys to change the value up or down by one unit at a time. You can also use the tab key to switch between the different elements. System Time
		Clicking the System Time button (the one with the icon of a computer screen) will show you what the sky looks like from your current location right now, i.e.: the time on your computer. For example, if you've been adjusting the time but now wish to see the sky as it looks at this moment, pressing this button will reset the current view's time. Note: If your current view's location is in a different time zone than your default setting, Starry Night will automatically adjust the time to your new location's local time. If your current location is in space or on another planet, the time is set to Universal Time, the astronomical standard based on the time at Greenwich, England. Time Step
		The speed at which time flows is adjusted by the Time Step. Initially this is set to be three minutes but this can be changed to any setting you like. To adjust the time step's number, select the number and use the little increment buttons to raise or lower the number's value. You may also use the keyboard's "+" and "-" keys, or simply type in the number you wish. By default, the time step's unit is set to "minutes", but this can be switched to seconds, hours, days, sidereal days, lunar months, sidereal months, or years. To adjust the time step's unit, click the unit, then use the up/down mini buttons to raise or lower its value. You may also type in the first letter of the unit you wish to change to. (Type "m" for minutes, "s" for seconds, "h" for hours, "l" for lunar month, and "t" for sidereal month). Daylight Savings Time You may adjust the time to reflect Daylight Savings Time (if it applies to the current viewing situation) by clicking on the small Sun icon to the left of the time display. Starry Night uses this information to calculate universal time. When daylight savings is on, the Sun icon will light up in yellow. To set Daylight Savings Time for your Home Location see Setting Your Home Location in the Getting Started Chapter. Setting Julian Dates The Julian Date represents the number of days that have elapsed since January 1, 4713 BC. Astronomers sometimes use Julian dates in order to avoid the problems resulting from historical calendar changes. To see the current time expressed as a Julian date, click the Julian button to open the Julian Time window. If you'd like to set the current time to a specific Julian date, type in the Julian date you wish to view, then click the Set Time button.

The Current Time

The Time Palette

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