The TPE Web lets you move quickly to a particular date or astronomical event using the date and event controls at the top of the map. You can move one day at a time, return to the current date and time, enter a specific date, or jump directly to events such as Moon phases, solstices, equinoxes, and eclipses.
Using the date and event controls
The controls at the top of the map let you move through dates and events in several different ways.
From left to right, they are:
- Previous event – moves to the previous astronomical event
- Previous day – moves back one day
- Now – returns to the current date and time
- Calendar – choose a date from the calendar or enter one directly
- Events – browse astronomical events and select one to view
- Next day – moves forward one day
- Next event – moves to the next astronomical event
Choosing a specific date
To go to a specific date, click the date at the top of the map to open the calendar. From there, you can select a day from the displayed month, click the arrows to move between months, or use the month or year drop-down menus to move more quickly through the calendar.
Note: The year menu displays 10 years before and 10 years after the currently selected date.
You can also enter a date directly in the date field. Type the date you want – using either a readable or numeric format – then press Enter to go to that date. You can use this method to enter dates outside the 10-year range shown in the year menu.
TPE Web always displays information for a specific date and time. Selecting a month does not display the entire month at once. If you want to plan for a date in July, for example, navigate to July and then select a particular day, or type the date directly into the date field.
Moving one day at a time
Use Previous day or Next day to move backwards or forwards by one day.
This is useful when you want to compare nearby dates without reopening the calendar – for example, to see how the position of the Sun or Moon changes from one day to the next.
Navigating astronomical events
TPE Web can also take you directly to significant astronomical events.
Use Previous event and Next event to step backwards or forwards through events. When you select one of these controls, TPE Web changes both the selected date and time to the previous or next event. Events include:
- New Moon
- First Quarter Moon
- Full Moon
- Third Quarter Moon
- Lunar perigee
- Lunar apogee
- Maximum and minimum lunar declination
- Solstices
- Equinoxes
- Lunar eclipses
- Solar eclipses
Browsing and selecting events
If you want to see what events are coming up rather than stepping through them one at a time, select Events.
The Events window lists astronomical events by date and time. You can browse the list, select the event you want, and then click Select.
TPE Web changes the selected date and time to the exact time of the chosen event.
Solar eclipses are also available from the Solar eclipses tab in the Events window.
Keyboard shortcuts
You can also move between dates and events using the keyboard:
| Action | Shortcut |
|---|---|
| Previous day | P |
| Next day | N |
| Previous event | Ctrl + P |
| Next event | Ctrl + N |
The event time may not be the best time to photograph it
Navigating to an event takes you to the exact time of the astronomical event. That does not necessarily mean it is the best time to photograph the event.
For example, you typically won’t want to photograph the Moon at the exact instant of Full Moon. Full Moons are often best photographed near moonrise to the east on the evening before the official Full Moon, or near moonset to the west the following morning. Check the timing and direction for your selected location, as the relationship between moonrise or moonset and sunrise or sunset varies significantly by location and month.
Similarly, you won’t see the Moon at the instant of New Moon because its illuminated side is turned away from Earth. If you’re looking for a young crescent Moon, check the evenings following New Moon instead.
Finding a young crescent Moon
New moons are typically best shot to the west just after sunset, 1-3 days after new moon.
After navigating to New Moon, move forwards one or more days and look for Best crescent vis. in the Timeline. While actual visibility will depend on atmospheric conditions, your observing location, and other local factors, TPE Web shows the estimated best time for viewing the young crescent together with a visibility rating from A to F.
The visibility rating uses the Yallop method:
| Rating | Description |
|---|---|
| A | Easily visible to the unaided eye |
| B | Visible under perfect atmospheric conditions |
| C | May need optical aid to find the thin crescent Moon before it can be seen with the unaided eye |
| D | Can only be seen with binoculars or a telescope |
| E | Below the normal limit for detection with a telescope |
| F | Not visible. Below the Danjon limit |
Note that some say the Danjon limit is dead, but for most photographers without specialist equipment, the above rating remains a useful guide. For more background on how soon after New Moon a crescent may become visible, see “ What’s the youngest moon you can see? ”.
