Zodiacal Light — False Dusk or False Dawn

Star Walk
5 min readMar 17, 2023
Image Credit: Vito Technology, Inc.

Have you ever noticed a mysterious cone of light in the sky during the spring or autumn months? This could be the rare celestial phenomenon known as the zodiacal light. Read on to learn where this eerie light comes from and how to find it with the help of the astronomy app Sky Tonight.

What is the zodiacal light?

Zodiacal light is a hazy pyramid of light located above the sunrise or sunset point on the horizon. It’s centered on the ecliptic — the Sun’s path in the sky that crosses the well-known zodiac constellations. This is why it’s called the zodiacal light.

You might have noticed the zodiacal light, not even realizing what it is. It looks like the light of the nearby town or the lingering twilight. But don’t be fooled by it! In spring, in both hemispheres, the zodiacal light occurs right after the real dusk, so it’s called “the false dusk.” In autumn, the zodiacal light occurs just before the real dawn and is known as “the false dawn.” Note that the seasons in the Northern and Southern hemispheres are reversed.

You might also confuse the zodiacal light with the Milky Way, and that’s not surprising. It is comparably bright and even milkier in appearance, but you can tell the zodiacal light by its pyramidal shape. Under a dark sky, you can sometimes even see the real Milky Way crossing with the zodiacal light.

What causes the zodiacal light?

You can distinguish the zodiacal light from the real twilight by the fact that it has no reddish tinting — the pink color is the effect of the Earth’s atmosphere, but the zodiacal light comes from outside our atmosphere. In fact, it’s just the Sun’s light reflecting off dust grains orbiting our star in the inner Solar System. But where do these dust grains come from? Scientists have long assumed that the space dust that causes the zodiacal light is produced by asteroids and comets. However, the new research shows that the main source of this cosmic dust may be dust storms on Mars.

When to see the zodiacal light?

In both hemispheres, at mid-latitudes, the zodiacal light is best seen around the equinoxes. In tropical latitudes, it can be seen year-round.

Spring zodiacal light — false dusk

In spring, the zodiacal light can be seen for about an hour in the western sky. Start observing the “false dusk” about 90 minutes after sunset.

In the Northern Hemisphere, it appears in the sky in late February, reaches its maximum brightness around the March equinox, and lasts until early May.

In the Southern Hemisphere, the zodiacal light appears in the sky in late August, reaches its maximum brightness around the September equinox, and remains until early November.

Autumn zodiacal light — false dawn

In autumn, the zodiacal light can be seen for about an hour in the eastern sky. Start observing the “false dawn” about 90 minutes before sunrise.

In the Northern Hemisphere, it appears in the sky in late August, reaches its maximum brightness around the September equinox, and remains until early November.

In the Southern Hemisphere, the zodiacal light appears in the sky in late February, reaches its maximum brightness around the March equinox, and lasts until early May.

How to see the eerie light?

First and foremost, you should find a place with a dark sky, far away from the light-polluted cities. The zodiacal light is so hazy that any bright light sources can wash it away. And the natural light source — the Moon — is no exception. Fortunately, this year’s March equinox falls on the New Moon, so it won’t be a problem. But you can also enjoy the crescent Moon bathed in zodiacal light a few days later, and its minimal illumination won’t hinder the view.

How to locate the zodiacal light with Sky Tonight?

The stargazing app Sky Tonight will help you spot the zodiacal light. You’ll do it easily with the Sun as a reference point. First, find out the time of the zodiacal light in your location:

  • Find the Sun in the search bar, tap on its name, and go to the Events tab.
  • In the time machine section, select the date you want to observe the zodiacal light. The next best date to see the brightest zodiacal light is March 20, 2023.
  • In the Visible Passes section, you’ll see the sunrise, noon, and sunset times in your location for the chosen date.
  • In the Northern Hemisphere, add 90 minutes to sunset time — it’s when you should start looking for the zodiacal light.
  • In the Southern Hemisphere, subtract 90 minutes from sunrise time — it’s when you should start looking for the zodiacal light.

If you don’t want to miss the moment, set a reminder:

  • Set the needed date and time in the time machine section.
  • Tap the bell icon in the right corner of the time machine and adjust the reminder.

On the chosen date and time, go to a place with dark, clear skies and find the zodiacal light’s direction. Depending on your hemisphere, it’s located above the sunrise or sunset point, so you need to find this point:

  • In the Northern Hemisphere, tap the blue sunset time on the chosen date in the Sun’s Visible Passes section, and the app will show you the Sun’s location on the sky map.
  • In the Southern Hemisphere, tap the blue sunrise time on the chosen date in the Sun’s Visible Passes section, and the app will show you the Sun’s location on the sky map.
  • Tap the blue compass button at the bottom right of the screen. The app will use your device’s location to adjust the image to match the real sky above you.
  • Follow the white arrow on the screen to the sunrise or sunset point. This is the direction to see the zodiacal light extending from the horizon.

Bottom line

The zodiacal light is a rare and beautiful celestial phenomenon that looks like a hazy pyramid of light rising from the horizon. It occurs just after dusk near the vernal equinox and just before dawn near the autumnal equinox. To observe it, you will need to find a dark suburban sky.

Good luck on your stargazing journey!

Text Credit: Vito Technology, Inc.

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