How to observe the zodiacal light?

Some spring evenings or some autumn dawns are suitable for observing the zodiacal light. What is it about ? Here are some tips for observing this glow in the sky.

The month of September 2021 lends itself well, among other astronomical phenomena, to the observation of the zodiacal light. In the morning of Sunday, September 12, in particular, you can try to look for this amazing glow in the sky, just before sunrise, towards the east.

Where does this luminosity come from? What advice should be followed to observe it properly? Here is everything you need to know about the zodiacal light, to look at it in the best conditions, in spring as in autumn.

How to observe the zodiacal light?

In the days around the spring equinox, you may attempt to see the zodiacal light in the evening. Observation is generally possible ” during the first 10 days of April », Indicates Jean-Luc Dauvergne, member of the French Astronomical Association. Same thing around the autumn equinox, in September.

Looking at the zodiacal light takes a little more anticipation than just gazing at the moon. Moreover, this glow is easier to see when our natural satellite is absent from the sky (at the time of the new moon). ” The zodiacal light is a rather faint glow. You must stay away from any source of light pollution. If one manages to find a place that is dark enough, then it can almost become annoying », Continues the specialist. We will therefore have to forget the big cities …

Zodiacal light, seen from Australia. // Source: Flickr / Public Domain / Dylan O’Donnell (cropped photo)

Zodiacal light is perceptible above the western horizon in the spring, and above the eastern horizon in the fall. Jean-Luc Dauvergne advises looking for a ” oval glow truncated by the horizon At dusk. In astronomy, this term is used to refer to the period before sunrise or after sunset. The center of the sun is between 12 ° and 18 ° below the horizon. The best time to observe the zodiacal light should be around 1 hour after sunset, or 1 hour before (depending on whether you are attempting to observe it in March / April or September / October).

Where do you have to go to hope to see this light show? In France, people living on the “ Atlantic rim Are well placed in the spring (because they are in the west) to try to observe the zodiacal light. Provided, however, that you are not in a big city, ” like Bordeaux », Specifies Jean-Luc Dauvergne. And in autumn, you will understand, people living in the east of France are better placed.

Where does the zodiacal light come from?

Why is it visible at specific times, in spring (in the evening, at dusk) and in autumn (in the morning, before dawn)? This corresponds to the times when the zodiac is perpendicular to the horizon.

In astronomy, the zodiac is the place in the sky in which we see the movement of the Sun (which seems to cross 13 constellations in one year), the Moon and the planets. The zodiac extends around the ecliptic, that is to say the path drawn by the Sun each year, seen from the Earth.

Source: Nino Barbey for Numerama

« Depending on the inclination of the Earth on its axis, the zodiacal light will be more or less straight with respect to the horizon », Explains Jean-Luc Dauvergne. In other words, the ecliptic must form an angle with the horizon which is as perpendicular as possible. From Europe, these conditions are met in spring and autumn.

As for the observable glow, it is explained by the reflection of sunlight by dust from space. These particles mainly come from comets that have come closer to the Sun and ejected matter. ” You have to imagine that this microscopic dust is rough. Think of the Moon: when it is lit from the front, it is brighter. Here, it’s the same phenomenon », Continues the representative of the French Astronomical Association. The Paris observatory indicates that the zodiacal light can still represent 60 % of the brightness of a moonless night.

You now have all the keys in hand to try to see the zodiacal light, after sunset or before sunrise depending on the time of year. Good observation!

Look at the world from space

Article originally published on April 03, 2019 and updated on September 11, 2021

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