This winter, people have been amazed by the different celestial phenomena. But observing the Northern Lights and fireballs, for example, requires certain conditions.
Spring-winter is a good time to observe different light phenomena in the sky.
Many people share their observations on social media or on the Astronomical Society of Finland’s Skywatcher service. In late February, for example, the Northern Lights were so spectacular in the night sky that a light show prompted a Finnair captain to change his route to show them.
There are several reasons.
1. The conditions for observations are good
In order for the various celestial phenomena to catch the eye, it must of course be sufficiently dark. In Finland, it means that it is best to make observations from dusk in autumn to spring.
– In the summer, of course, it won’t work. But now that people are outside in the evening and it’s dark, it’s possible to make observations, says Visuri.
In spring and winter, the weather is often more favorable for observing celestial phenomena.
– Autumn is statistically a cloudier time. At the end of February, the evenings start to be significantly brighter and the weather is getting better and better this spring winter.
In the clear evening sky, there are also stars that may twinkle at times. That’s not really the case, but turbulent wind somewhere in the atmosphere causes the phenomenon in question. Typically jet streams occur at an altitude of 10 kilometers.
– It’s like a lens that constantly changes its shape, which also changes the path of the light beam a little.
Sometimes the twinkling star may also change color. This is because some stars have a longer light beam than others. Then the light beam has time to change its route sharply and sometimes even break up into colors.
2. April is the golden month for halos
Halo phenomena are dependent on seasonal weather changes, as a halo requires that there are enough ice crystals in the atmosphere. The most likely time of year for the phenomena is April.
– In the circles of star enthusiasts, they talk about Halo April. But you have to remember that halos are not actually real objects, but different ways of light rays refracting in the atmosphere.
Typical halo phenomena observed in winter are light pillars and the 22-degree halo ring around the Sun.
The tweet shared by the Ursa Sky Watch observation service on November 28, 2021 shows halo photos taken by the public from different parts of Finland.
Pillars of light appear especially around midwinter during severe frosts. Instead, with the 22 degree halo ring, it is possible to observe the so-called side suns at the same time.
– They appear with the Sun at the same height on opposite sides. At best, the side suns look almost as bright as the Sun itself, says Visuri.
3. The sun is more active than usual
The northern lights are visible regardless of the season. This past winter, however, the sun has been more active than usual, which has increased the chances of spotting the northern lights around Finland.
– The sun’s activity goes in 11-year cycles. Now the solar activity period has been on the rise and this is predicted to continue even until 2026. However, the sun’s cycles are unpredictable.
Northern lights are created when electrically charged particles erupting from the sun collide with the atmosphere.
On February 28, 2023, Ursan Taivaanvahti shared a tweet about the spectacular aurora borealis that the public had observed in Pyhäjärvi and Lieksa.
4. More long-lived, bright meteors in spring
Fireballs are bright shooting stars that are created when a meteoroid, i.e. a small piece of rock, arrives from outer space into the earth’s atmosphere.
Fireballs usually survive in the atmosphere for longer than a few seconds, while dimmer shooting stars typically only last a couple of seconds.
In the spring and winter, long-lasting, bright meteors appear a little more in the early evening in Finland. This is due to the tilt of the Earth’s axis of rotation and the way bodies rotate around the Sun.
– However, the difference is so small that it doesn’t really explain the fireballs that have been continuously fed recently.
On October 28, 2022, Ursan Taivaanvahti tweeted about a fireball spotted by a follower.
5. Chance also plays a part in the game
The appearance of Jupiter and Venus rolling in the sky at this time of the year is purely coincidental. Like Earth, other planets also revolve around the Sun. Because of this, the best time to observe each planet varies.
Observing all other planets, except Venus, also requires dim and clear skies.
– Venus is visible from a clear sky most of the time also during the day. All other planets require the Sun to set on the horizon before they can be distinguished with the naked eye, says Visuri.
If the point of light visible in the sky moves, it is probably a satellite.
– Up to ten satellites can be detected in one field of view. Their orbits are lowest at an altitude of about 300–400 kilometers.