The chart rim is a level, geometric horizon. A ridge or tree can hide a star above that line. Air also bends light near the horizon; this model leaves that effect out. An above-horizon position is only one part of an actual sighting.

Try it. Find Antares in the reading table. Imagine a ridge higher than its altitude. Sketch where that ridge would hide the star.

The circle is not a survey of the skyline at Sunset Point.

Sources [15] [2] [3] · Paired activity 3

July 15, 2026 at 11:00 PM MDT
2026-07-16T05:00:00Z

Astronomical night
Moon 4.7% illuminated

Altitude measures an angle above a level horizon, not a distance from Earth. Zero degrees is at the rim; 90 degrees is directly overhead, at the zenith. On this chart the 30-degree and 60-degree rings help you read the climb toward the center.

Try it. Compare Vega with Antares. Point to the higher star on the chart before reading their altitudes.

A star plotted nearer the center is higher in the sky, not physically nearer to you.

Sources [15] [1] · Paired activity 1

July 15, 2026 at 11:00 PM MDT
2026-07-16T05:00:00Z

Astronomical night
Moon 4.7% illuminated

This view looks upward. With north at the top, east belongs on the left. The direction you choose to face moves to the bottom, nearest you. Rotating the drawing changes its orientation while every object's altitude and true-north bearing stay the same.

Try it. Change Face from south to north. Watch Polaris move on the page, then check that its two angles did not change.

Azimuth runs clockwise from true north: N 0, E 90, S 180, W 270 degrees. It is not a magnetic compass reading.

Sources [15] [7] · Paired activity 4

July 15, 2026 at 11:00 PM MDT
2026-07-16T05:00:00Z

Astronomical night
Moon 4.7% illuminated

Polaris lies close to the north celestial pole, but not precisely on it. Its small daily circle makes it a useful northward landmark. At this reference latitude, the pole itself is about 37.6 degrees above the level northern horizon.

Try it. Step forward an hour four times. Compare Polaris with Schedar: which changes altitude less over those steps?

Polaris is a direction clue, not the brightest star. The pole's height follows from the observer's latitude.

Sources [7] [15] [2] · Paired activity 4

October 15, 2026 at 9:00 PM MDT
2026-10-16T03:00:00Z

Astronomical night
Moon 26.9% illuminated

Earth's rotation carries a familiar star pattern across your local sky. The stars' arrangement is effectively unchanged over an evening, even while their altitude and bearing change. A flat chart projection can stretch the apparent drawing as it approaches the rim.

Try it. Load the winter exercise. Compare Sirius at 9 p.m. and 11 p.m.; describe the change using both altitude and bearing.

This is apparent daily motion. The two-hour jump is a teaching comparison, not a moving live view.

Sources [7] [8] [1] · Paired activity 1

January 15, 2026 at 9:00 PM MST
2026-01-16T04:00:00Z

Astronomical night
Moon 6.9% illuminated

As Earth travels around the Sun, its night side faces different directions in space. A star therefore occupies a different place at the same clock time on another date. The spring pair keeps Denver's daylight-saving offset the same on both dates, making that comparison easier to read.

Try it. Compare Arcturus on April 15 and May 15 at 10 p.m. Predict which position is higher, then open the pair.

A seasonal name does not mean a pattern appears only in that season; the hour matters too.

Sources [9] [15] [1] · Paired activity 2

April 15, 2026 at 10:00 PM MDT
2026-04-16T04:00:00Z

Astronomical night
Moon 2.5% illuminated

Vega, Deneb and Altair form an asterism: a recognizable pattern. They belong to Lyra, Cygnus and Aquila respectively. Our line segments help you connect the names; they are neither physical links between stars nor official constellation boundaries.

Try it. Find all three corners. Switch the pattern lines off, then try identifying the corners again from their labels and bearings.

These modern finding aids represent only a small part of the many ways people understand the sky.

Sources [8] [1] · Paired activity 3

July 15, 2026 at 11:00 PM MDT
2026-07-16T05:00:00Z

Astronomical night
Moon 4.7% illuminated

Apparent visual magnitude ranks how bright a star appears from Earth: lower numbers mean brighter stars. The catalogue gives Sirius a lower magnitude than Procyon. Point sizes here suggest that ranking; they do not show stellar size, and they do not simulate tonight's visibility.

Try it. Read the catalogue magnitudes for Sirius, Betelgeuse and Procyon. Rank them from brightest to faintest before comparing their dots.

Catalogue brightness is a reference value. Variable stars and local observing conditions are not animated.

Sources [1] [18] · Paired activity 1

January 15, 2026 at 11:00 PM MST
2026-01-16T06:00:00Z

Astronomical night
Moon 6.5% illuminated

Civil, nautical and astronomical twilight are defined using the Sun's center at 6, 12 and 18 degrees below the horizon. These thresholds describe geometry. They do not tell you exactly when a particular star becomes visible.

Try it. Open the summer pair. Compare the Sun's altitude and the twilight label at 8:30 p.m. and 10:30 p.m.

No sunrise or sunset time is calculated. The real skyline, refraction, clouds and artificial light are absent.

Sources [12] [15] · Paired activity 3

July 15, 2026 at 8:30 PM MDT
2026-07-16T02:30:00Z

Daylight
Moon 4.2% illuminated

The illuminated fraction describes the sunlit part of the Moon's apparent disk, not a fraction of its maximum brightness. Ordinary phases come from the changing Sun-Earth-Moon geometry, rather than Earth's shadow falling across the Moon.

Try it. Compare the July 15 and July 29 readings. Write down the fraction and broad phase label for each night.

The circular Moon marker shows position only. It does not depict the lunar disk's shape, orientation or true angular diameter.

Sources [11] [3] [15] · Paired activity 5

July 29, 2026 at 11:00 PM MDT
2026-07-30T05:00:00Z

Astronomical night
Moon 99.6% illuminated

A phase reading and a direction reading answer different questions. Check the Moon's altitude as well as its illuminated fraction. A negative altitude places its modeled center below the geometric horizon at this location and instant.

Try it. Start on July 15 at 11 p.m. Find the Moon in the table even if it has no marker inside the chart. Then load the other July night.

An above-horizon Moon still does not establish a clear view. No moonlight brightness or skyglow forecast is supplied.

Sources [11] [15] [3] · Paired activity 5

July 15, 2026 at 11:00 PM MDT
2026-07-16T05:00:00Z

Astronomical night
Moon 4.7% illuminated

We view the Milky Way's disk from inside it. The dashed line marks the calculated Galactic equator, giving a direction reference across the sky. Its width, dashes and color are drawing choices; they cannot describe dust lanes or how bright the Milky Way will appear.

Try it. Trace the dashed guide across the summer scene. Toggle it off and compare it with the Summer Triangle's straight finding lines.

This is derived geometry, not a night photograph. Whether the Milky Way is visible must be observed in the field.

Sources [4] [10] [5] · Paired activity 3

July 15, 2026 at 11:00 PM MDT
2026-07-16T05:00:00Z

Astronomical night
Moon 4.7% illuminated

When Denver leaves daylight saving time, the repeated hour has two different UTC instants. The sky keeps moving while the clock repeats. This deck requires an occurrence choice instead of silently choosing one. In spring, a skipped clock time has no matching instant.

Try it. Load the November repeated-hour activity. Compare the MDT and MST choices and read the UTC label for each.

The location always uses America/Denver, even if your device is elsewhere. Future time-zone rules may change.

Sources [16] [15] · Paired activity 8

November 1, 2026 at 1:30 AM MDT
2026-11-01T07:30:00Z

Astronomical night
Moon 56.2% illuminated

A date needs a year as well as a month and day. The date controls accept February 29 in 2028 and reject it in 2026. They also reject dates outside the supported local years, 2020 through 2035, rather than extending the classroom's stated range.

Try it. Use the leap-day pair, then enter 2026-02-29 in a text-capable date control. An invalid request must leave the last valid sky intact.

A UTC date can differ from the Denver date. Both are shown so that another person can reproduce the same instant.

Sources [15] [17] · Paired activity 6

February 29, 2028 at 10:00 PM MST
2028-03-01T05:00:00Z

Astronomical night
Moon 19.8% illuminated

NPS stargazing guidance suggests allowing roughly 20 to 30 minutes for dark adaptation and keeping lights restrained. The red-display option changes this page's palette. It does not dim your hardware, other apps or the real sky.

Try it. Switch between night, high contrast and red display. Check that the astronomical readings stay identical. Choose a readable setting and lower device brightness yourself when appropriate.

Screen color is not a guarantee of preserved night vision. Consider other observers and keep lights out of their eyes.

Sources [13] · Paired activity 3

July 15, 2026 at 11:00 PM MDT
2026-07-16T05:00:00Z

Astronomical night
Moon 4.7% illuminated

A calculation can supply a date, direction and modeled altitude. It cannot report what you actually saw. On paper, separate the calculated reading from your own description of clouds, obstructions and detected objects. Leave unobserved details blank.

Try it. Use the print deck's blank log. Record a model value in one column and a real observation in the other only after observing.

These are learning examples, not forecasts, telescope instructions, access advice or a park program schedule.

Sources [15] [6] [14] · Paired activity 2

July 15, 2026 at 11:00 PM MDT
2026-07-16T05:00:00Z

Astronomical night
Moon 4.7% illuminated