If you’re already familiar with the basics in The Photographer’s Ephemeris Web, the next step is to take a closer look at how conditions change throughout the day. If you’re new to TPE Web, we recommend starting with TPE Web Orientation and Basics, which introduces the main planning screen and shows you how to choose a location and date.
In this tutorial, we’ll use a location near Mount Sneffels, Colorado, to explore the information TPE Web provides for a selected day. We’ll work through the Timeline and altitude chart, see how changing the time affects the Sun and Moon information shown on the map, and look at how TPE Web displays twilight and shadows.
By the end, you’ll have a clearer understanding of how these parts of the planning screen work together and how you can use them to explore the timing and conditions for photographs of your own.
Choosing a location
First things first: we need to choose a location for this tutorial that lets us illustrate the relevant features. To get started, let’s find our location. Click the Search button above the map to open the search form.
- Type “ Mount Sneffels, Colorado, USA ”
- Click Search or press Enter to perform the search. (If you’re a PRO subscriber, you’ll see results as you type.)
- Click Go on the first displayed result
You should see the primary map marker (the red pin) at the summit of Mount Sneffels, one of Colorado’s finest fourteeners (summits over 14,000 ft). If you want to follow along, set the date to August 3, 2021. One nice thing about TPE Web is that you can look backward as well as forward in time: the information is correct for the date and the red pin position you have selected.
To change the date in the calendar, click the date selector, choose the date from the calendar, or just type it into the text field and press Enter. Your screen should look something like this:
- Primary pin is at the summit of Mount Sneffels
- Date is set to August 3, 2021
An introduction to the TPE Web Timeline
Let’s move the red pin to the southwest, along the trail above the highest of the three Blue Lakes. Why there? Why then? I was there and took some photos!
Sunrise from Blue Lakes Pass looking down at the upper Blue Lakes. August 2009
Now, look at the Timeline in the right-hand sidebar. Each event in the Timeline includes its time and azimuth. Azimuth describes a compass direction, measured clockwise from true north: 0° is north, 90° is east, 180° is south, and 270° is west. On the map, the coloured lines show these directions from the red pin.
You can see from the Timeline that the first “ event ” for August 3, 2021, is moonrise at 1:48 a.m.
The next three events are the three standard twilights: astronomical (when the Sun is 12–18° below the horizon), nautical (6–12°), and civil (6–0°). After that comes sunrise, golden hour, moon transit, then Sun transit, and so on. We define golden hour as the time between sunrise and when the Sun climbs to +6° above the horizon (and, in the evening, the time between when the Sun descends to +6° and sunset). Transit is the time when the Sun or Moon crosses the local meridian (due north or due south) – typically this is also the instant of highest altitude (elevation angle) above the horizon, known as culmination.
The times of moonrise and moonset vary significantly through the month; certain days will not even have a moonrise or moonset event. The other information in the moonrise box is the azimuth of the moonrise, its phase, and its percentage visibility. If this were a New Moon or a Full Moon, there would be additional information in the box.
- Recentre the red pin on the map
- Timeline for August 3, 2021
- Moonrise at 1:48 a.m. is the first event of the day
Size is everything
At this point, I want to draw your attention to screen size. I am using a small screen for this tutorial, and not all of the event information in the Timeline is visible at this size. If you have a small screen, just scroll in the Timeline to view all the events for the day.
When panning the map in search of a location, it is sometimes desirable to have a bigger map area. You can collapse both the left-hand navigation bar and the right-hand sidebar using the following controls:
- Expand or collapse the left-hand navigation bar
- Expand or collapse the right-hand sidebar
For the next section of the tutorial, keep the right-hand sidebar visible. You may collapse the left-hand navigation bar.
Using the TPE Web Altitude Chart
The chart is at the bottom of the screen: it displays the altitude (elevation angle) of the Sun and Moon over the course of the selected day, with the Sun shown in orange and the Moon shown in blue.
To change the time of day, click in the chart and then drag either to the left or the right. The legend moves as you drag the chart and shows the time selected, plus the azimuth and altitude information for the Sun (orange) and the Moon (blue). It is important to note that since both azimuth and altitude are expressed in degrees, we add a + or – sign to altitude values to distinguish them from azimuths.
Clicking on an event in the Timeline sets the chart to that time. Try it now: click on moonset in the Timeline. If your date is still set to August 3, 2021, the chart jumps to 4:50 p.m. In the screenshot, I have clicked on the moonset event for the day. If the selected time of day matches a Timeline event, the event title is shown in the chart legend:
- Sun azimuth line
- Altitude chart
- Chart legend
- Selected event
With the moonset selected, the Sun azimuth line shows the bearing of the Sun from the red pin at 4:50 p.m., the selected time, as displayed in the legend. The azimuth line for the Sun is orange (the Moon azimuth line would appear in blue, but this is the time of moonset).
On the map, the thicker lines show the azimuths of sunrise, sunset, moonrise, and moonset. The thinner orange and blue lines show the current azimuths of the Sun and Moon at the time selected on the chart. As you move the chart, these lines rotate to reflect their changing positions in the sky.
Move the chart again and watch the lines on the map: notice that the thin Sun and Moon azimuth lines move around between the thicker rise and set lines. If the Sun or Moon lies above the horizon, these azimuth lines show the bearing you would look along from the red pin position at the selected time.
You can make finer adjustments with the chart. Click in the chart: now use the left and right cursor keys on your keyboard to adjust the time backward or forward in ten-second increments.
Using Twilight Information for Night and Blue Hour Photography
The definitions of the three twilight states are as follows: astronomical twilight occurs when the Sun lies between 18° and 12° below the horizon; nautical when the Sun lies between 12° and 6°; and civil when the Sun lies between 6° and 0°. You can find more details on these terms on Wikipedia.
The light of twilight is variously described as more “ even, ” muted, or blue than full sunshine. This lower dynamic range suits the camera and can make for great landscape photographs. The blue “ hour ” is a myth; the actual length of twilight varies significantly by season and by latitude: it is short in the tropics but long in the polar summer. (Read more: Magical Gold and Blue: Confusion in the Twilight Zone)
Twilight can affect photography in a number of important ways. At temperate latitudes, such as here in Colorado (40° N), late nautical and early civil twilight offer more intense sky colours than late civil twilight. And alpenglow will typically last until 10–15 minutes before sunrise – roughly midway through the typical civil twilight period.
It is important to note that, though the Sun may not yet have risen (or may have already set), twilight is still directional, which is why the Timeline includes the twilight azimuth information, along with the twilight start or end time. The azimuth corresponds to the brightest point on the horizon.
Let’s look at using the twilight information in the Timeline for a practical example from our Blue Lakes location on August 20, 2021.
Imagine you wanted to do some night photography of the Blue Lakes and the surrounding mountains with a clear, starry sky overhead. When would be a suitable time to shoot the scene during the night of August 20, 2021?
- Moonset
- Astronomical twilight starts
- Civil twilight starts
If you’re looking to shoot a clear, starry sky, you probably want it to be truly dark, i.e., after the Moon has set and before astronomical twilight begins. Using the information in the Timeline, you can see that on this particular night, there’s only a small window of opportunity: the Moon sets at 4:07 a.m., but astronomical twilight begins at 4:55 a.m. It’s likely that the best time is somewhere between 4:15 and 4:40 a.m. Once astronomical twilight begins, objects such as the Milky Way will become less visible in the sky, disappearing altogether as nautical twilight progresses.
Shadows in TPE Web
We all know that as the Sun gets lower in the sky, shadows lengthen toward infinity. The Moon casts shadows too, especially noticeable at Full Moon. In TPE Web, shadows are represented by the shadow line (brown for Sun, dark blue for Moon). (NOTE: TPE Web limits the length of its shadow and azimuth lines to 200 miles.)
Set the date to August 3, 2021, then click the sunrise event in the Timeline. Now slowly move the chart forward from sunrise. The darker line extending from the red pin in the direction opposite the Sun azimuth line is the shadow line. It shows the direction in which a shadow would fall on level ground. Because the Sun is still low at sunrise, the shadow line is long.
Now move forward through the morning by dragging the altitude chart until a later time is selected. As the Sun rises higher in the chart, its azimuth line changes direction on the map and the shadow line becomes shorter.
The shadow line provides a relative visual guide rather than the measured shadow length for a particular object. Actual shadows will also depend on the object’s height and the slope of the ground.
The thinner line extending through the red pin shows the continuation of the Sun’s current azimuth in the opposite direction – the direction in which sunlight is travelling across the map. It can help you assess which landscape features or subjects lie in the path of the light, although actual illumination will depend on terrain and other obstructions.
- Sun azimuth extension line
- Sun shadow line over the Sun azimuth extension line
