Videos

Animations of How the Sky Moves

An introduction to how the sky changes throughout the night and the seasons is presented in Chapter 3 of NightWatch. This knowledge is essential to finding your way around the night sky. To supplement the chapter and demonstrate sky motions, here is a series of time-lapse animations created by Alan Dyer using StarryNight™ desktop software. (Some scenes depict the southern-hemisphere sky, as a complement to Chapter 12.) Videos may take a moment to play with the best resolution.

As the Earth Turns by Night

Our first pair of animations shows the movement of the sky as viewed from 45° north latitude. The second pair is from 30° south latitude. The vertical line at the center of each graphic is the meridian, while the red grid lines indicate right ascension and declination.

Looking North from 45° North Latitude

Looking South from 45° North Latitude

Looking north on a September night, we see the sky rotating counterclockwise around an invisible point called the north celestial pole, near the star Polaris, in Ursa Minor. Stars and constellations close to the pole are called “circumpolar” because they never set below the horizon.

Looking south from the same location at the same time of year, we watch stars rise in the east (at left) and set in the west (at right). These stars and constellations in the south half of the sky are the seasonal patterns that change throughout the year.

Looking South from 30° South Latitude

Looking North from 30° South Latitude

Looking south on a September night, we observe the sky rotating clockwise around the south celestial pole, an invisible point in the dim constellation Octans (no bright star lies near the pole). Watch Crux (the famous Southern Cross) graze the horizon; at this latitude, it is essentially circumpolar.

Looking north from the same location at the same time of year, we enjoy the seasonal constellations. Many are familiar to northern-hemisphere observers, although they appear upside down to northern eyes. The stars still rise in the east and set in the west, but their motion is from right to left.

As the Earth Turns by Day

The first two pairs of animations illustrate the Sun’s seasonal motion as viewed from the northern hemisphere. The final pair depicts the Sun’s motion at the June and December solstices from the southern hemisphere. The faint line passing through the Sun is the ecliptic. The brighter horizontal line is the celestial equator.

Looking South from 45° North Latitude at the June Solstice

Looking South from 45° North Latitude at the December Solstice

In late June, the northern hemisphere is tipped sunward by the maximum amount. The Sun rises in the northeast, climbs to its highest position for the year and sets in the northwest. The June solstice produces the longest day and the shortest night.

In late December, the northern hemisphere is tipped away from the Sun. The Sun rises in the southeast, is relatively low in the south at noon and sets in the southwest. The December solstice produces the shortest day and the longest night of the year.

Looking South from 45° North Latitude at the March Equinox

Looking South from 45° North Latitude at the September Equinox

In late March, the noonday Sun sits halfway between its two extremes in altitude. It rises due east and sets due west. Day and night are temporarily of equal length, thus the term equinox (from the Latin aequus and nox for “equal night”) — in this case, the vernal equinox.

At the autumnal equinox in late September, the Sun charts the same course across the sky. But note which constellations are visible after sunset: Scorpius, Sagittarius and the stars of the Summer Triangle. Whereas after sunset in March, we see Orion and the winter stars.

Looking North from 30° South Latitude at the June Solstice

Looking North from 30° South Latitude at the December Solstice

In late June, the southern hemisphere is tipped away from the Sun by the maximum amount. The Sun doesn’t climb very high in the north as it drifts from east to west (right to left) across the sky on the shortest day of the year in the southern hemisphere. Here, it’s winter in June.

In late December, the southern hemisphere is tipped toward the Sun by the maximum amount. The Sun traces a path high across the northern sky, moving from east to west (right to left) on the longest day of the year in the southern hemisphere. It’s December — austral summer.

As Earth Orbits the Sun

For this pair of animations, a “snapshot” of the noonday sky was taken each day for a year, starting in December. By combining the photos, we created a time-lapse video showing the Sun’s changing altitude with the seasons.

Looking South at Noon from 45° North Latitude Throughout the Year

Looking North at Noon from 30° South Latitude Throughout the Year

The Sun rides low in the sky in winter and high in summer. But there’s a “twist” to the Sun’s seasonal motion. Because of the Earth’s elliptical orbit, the Sun traces an asymmetric figure-8 pattern (called the analemma) in the southern sky over the year, as viewed from the northern hemisphere.

Viewed from the southern hemisphere, the Sun traces the same figure-8 pattern, but it is “upside down” and in the northern sky. No matter where you live, the Sun’s altitude shifts over a range of 47 degrees throughout the year — equal to twice the 23.5-degree tilt of the Earth’s axis.

Looking South from 45° North Latitude Through a Year of Noonday Suns

Here, the Sun displays a full year of motion, with the Earth’s atmosphere “turned off” to reveal constellations in the daytime sky. As the year progresses, watch the midday Sun move along the ecliptic (marked in yellow) through the narrow band of 12 constellations called the zodiac. (The Sun also briefly passes through a 13th constellation — Ophiuchus.)

The seasonal shift of constellations occurs as Earth orbits the Sun, which makes the Sun appear to move around our sky through the zodiac. Planets dance back and forth due to their own orbital motions. The horizontal line bisecting the screen is the celestial equator.

The Changing Position of the Waxing Moon

These animations follow the waxing Moon just after sunset through 14 evenings in March and September 2024, as viewed from the northern hemisphere. Watch the Moon’s phase increase with each nightly step eastward. The paths are typical for early spring and early autumn. The curving green line is the ecliptic.

Looking South from 45° North Latitude in March

Looking South from 45° North Latitude in September

In March, the thin crescent Moon appears low in the west (at right). The Moon climbs higher each evening, as it waxes from crescent to first quarter. Because of the steep angle of the ecliptic, we see the waxing crescent at its highest for the year. (This is true for Mercury as well, which can be seen in the west here.) After the gibbous phases, a full Moon rises in the east (at left).

Six months later, in September, the ecliptic is a shallow arc low in the southern evening sky. Our time-lapse animation over a two-week period shows the waxing Moon emerging as a crescent in the southwest, growing to first quarter low in the south, then gibbous and, finally, full phase in the east. This full Moon is called the Harvest Moon.

The Motions of the Sun, Moon and Planets
March 2021 to March 2024

Watch as the five naked-eye planets trace out looping paths over a three-year period, from March 2021 to March 2024. The Sun moves along the ecliptic (the green line), with the planets drifting just above or below that line. The Moon darts quickly in and out of this sequence every month.

Play the video a few times and look for the following:

The motions of the Sun and planets carry them through the 12 zodiacal constellations, six of which are displayed here.
Swift-moving Mercury traces a looping path that keeps the little planet close to the Sun, while Venus’s larger orbital path carries it farther from the Sun. They both generally drift from west to east (right to left) through the zodiac. However, watch as they periodically retreat westward (left to right) in a celestial maneuver called retrograde motion. All planets do this.
In early 2021, Jupiter and Saturn are in Capricornus (at right). Over our three-year sequence, Jupiter drifts eastward (right to left) through Aquarius, Pisces and into Aries, spending about a year in each constellation, while slowpoke Saturn only reaches Aquarius, where it will stay for about two years. Both planets briefly display retrograde motion each year.
Faster-moving Mars appears in Sagittarius (far right) in early 2022. The red planet speeds along the ecliptic until late 2022, when it enters Taurus (far left), does a little retrograde backstepping for a couple of months, then resumes its eastward trek.

Eclipses of the Sun and Moon

These animations depict wide-field and close-up views of the April 8, 2024, total solar eclipse (TSE) and the March 13/14, 2025, total lunar eclipse (TLE), both visible from North America. The curved green line passing through the Sun and Moon is the ecliptic. The horizontal red line is the celestial equator, and the vertical white line is the meridian.

April 8, 2024, Total Solar Eclipse (Wide-Field View)

April 8, 2024, Total Solar Eclipse (Close-Up View)

From north and west of San Antonio, Texas, the Moon will completely hide the Sun at midday for over four minutes. At mideclipse, the Sun will be nearly 70 degrees above the horizon and due south. This animation speeds up the event.

While this close-up depicts the eclipse as it will be seen from San Antonio, the view will be similar from other locations along the path of totality. However, the shape of the corona and the appearance of red prominences will be different from this simulation.

March 13/14, 2025, Total Lunar Eclipse (Wide-Field View)

March 13/14, 2025, Total Lunar Eclipse (Close-Up View)

Watch the full Moon pass first through the Earth’s penumbral shadow (defined by the outer circle), then the umbral shadow (inner circle) to produce a total lunar eclipse, the next one visible from anywhere on Earth. At this eclipse, totality, when the Moon is completely inside the umbral shadow, will last 67 minutes. The partial phases will add another 76 minutes on either side of the event. This eclipse is visible from all of North and South America.

This closer view of the lunar eclipse shows the Moon drifting into the Earth’s barely perceptible outer penumbral shadow and its much darker inner umbral shadow. At each lunar eclipse, it is the Moon’s orbital motion around Earth that causes it to drift eastward relative to the starry background and move through our planet’s shadow. At most full Moons, the Moon passes above or below the shadow and there is no eclipse.

Video Montage of the August 21, 2017, Total Eclipse of the Sun

Video Montage of the September 27, 2015, Total Eclipse of the Moon

These two videos from Alan Dyer are montages of actual still images, time-lapses and movies taken at two recent total eclipses, here linked from his YouTube channel.

A Cosmic Zoom

Produced in 2009, this animation from the American Museum of Natural History presents a grand cosmic zoom from Earth to the edge of the known universe and back. Although somewhat dated, the simulation puts into perspective our very small place in the cosmos. An up-to-date description of this cosmic journey is presented in Chapter 2 (“The Universe in Eleven Steps”) in NightWatch.