Pine lichen and crescent moon

Fluorescent lichens and moss on a pine tree by illuminating with UV light.

Lichens on trees are usually completely harmless and are not a sign of disease. They only use the tree as a foothold and do not take nutrition from it. The lichens indicate clean air and serve as homes for insects, which attracts small birds.

Key facts about lichens on trees:

No harm: Lichens do not penetrate the bark, do not cause rot and do not harm the growth of the tree.

Epiphytes: They grow as so-called epiphytes, mainly on older trees, and get nutrition from water and air.

Air quality: Abundant occurrence of lichens is a sign of a good air environment.

Common types: Examples are leaf lichens such as lung lichen, beard lichen and crust lichen.

Ecological benefit: Lichens provide habitat for small animals, which benefits bird life.

In the sky, a slightly overexposed crescent moon with thin clouds in front.

Double Arc of Aurora

An aurora arc (northern lights arc) is the most classic and stable form of the northern lights. It looks like a luminous bridge spanning the sky, usually in a faint green color.

Characteristics and origin

Shape: The arc follows the Earth's magnetic latitudes. When you see an arc, you are actually looking at a small part of the giant aurora oval that surrounds the Earth's magnetic pole.

Color: The most common color is yellow-green, which is created when electrons collide with oxygen atoms at an altitude of about 100–150 km.

Development: A quiet arc is often the starting point. If geomagnetic activity increases, the arc begins to "dance", form folds (curtains) or split into several bands

A double aurora arc (aurora borealis double arc) occurs when the northern lights split into two or more parallel bands that stretch across the sky from horizon to horizon. The phenomenon is particularly captivating because it creates a symmetrical and structured view of the otherwise often chaotic light show.

How they are formed:

Magnetic field lines: Particles from the sun are guided by the Earth's magnetic field down towards the poles. A double arc often forms when geomagnetic activity increases, causing the aurora oval to expand and split into several discrete bands.

Geomagnetic substorms: During the most active phases of a "substorm", a single arc can quickly split into several parallel arcs.

Perspective: To an observer on the ground, the aurora appears as an arc due to the curvature of the Earth and the distance from the light show.

On the left, the constellations Cygnus and Cepheus run through one of the most star-dense and interesting parts of the Milky Way in the northern sky. These areas are particularly popular for both observation and astrophotography.

The "Handle" of the Big Dipper is seen at the top right, consisting of three bright stars that form a curved line. These stars are part of the larger constellation Ursa Major.Here are the three stars in the handle, counting from the dipper outwards:Alioth: The brightest star in the entire dipper. It is closest to the "dipper" itself.Mizar: The middle star. It is known to be a double star. If you have good eyesight (or binoculars), you can see a smaller, fainter star right next to it called Alcor.Alkaid: The star that sits at the far end of the handle.

Moon & planets

A cold, colorful afternoon in Vallentuna, Sweden. In the sky, a thin crescent moon with earthshine is visible, and to the left of the moon, the planet Saturn, and to the lower right, the planet Mercury.

Earthshine is an astronomical phenomenon in which sunlight is reflected from the Earth onto the dark night side of the moon, making the entire lunar disk faintly visible even when only a thin crescent is directly illuminated by the sun.

Mercury is the smallest planet in the solar system and the one closest to the sun. It is a rocky, so-called terrestrial planet with a surface filled with craters, which makes it very reminiscent of our moon.

Saturn is the second largest planet in the solar system and is best known for its spectacular and complex ring system. It is a gas giant that consists mainly of hydrogen and helium.