Venus setting in the west as daylight fades. While normal clouds have the classic ‘fluffy’ appearance, NLCs tend to appear more finely structured, with distinct and often straight lines or even grid-like patterns within them. While normal clouds will dim or block the light of the stars beyond, the finer structure of NLCs very often allow the light of stars through.Īnother way of identifying NLCs is through their structure. The blue-ish glow can be key to identifying NLCs from towns and cities, where our light pollution tends to under-light normal clouds with a yellow-orange glow. This can be very pale, but brighter displays can appear a stunning electric blue. While normal clouds appear darker against the night sky, noctilucent clouds seem to glow with a blue-ish tint. The angle of the Sun’s light is most likely to illuminate ice-crystals forming in our upper atmosphere around an hour or two after sunset and before sunrise. This will likely be the lightest part of the night sky at this time of year as the Sun lies just below the northern horizon. The formation of the ice crystals occurs high in the atmosphere in the colder air above Earth’s poles, so look north. It is also believed that dust and metallic particles from small meteors that are continuously entering and burning up in our upper atmosphere, contribute to the formation of these clouds. Scientists believe this may have been linked to the massive volcanic eruption of Krakatoa in 1883, which changed the abundance of certain gases and dust in our atmosphere, making water-ice more likely to form at higher altitudes. While many night sky phenomena such as the aurora and meteor showers have been observed and recorded for thousands of years, the first record of NLCs appears only to have been in 1885. These ice crystals are believed to be at a temperature of around -130 degrees centigrade and are only visible at certain latitudes (50 – 70 degrees from the equator), only appearing in the northern hemisphere between May and August each year. These appear when tiny ice crystals that form around 80km (50 miles) up in our atmosphere - higher than any other cloud – are under-lit by the Sun as it passes just below the northern horizon throughout the summer nights. This gives rise to a rare and beautiful phenomenon called noctilucent or ‘night shining’ clouds (NLCs). This is because the Sun does not set as far below the horizon during the summer months. Our planet’s tilt is responsible for the lighter nights we experience at this time of year. Notice how their silver-blueish glow is brighter than the surrounding sky, and different to the normal clouds, which appear much darker. Noctilucent or ‘night-shining’ clouds in the early morning skies above north Cornwall. It marks the point on Earth’s orbit around the Sun where the tilt of our planet leans the northern hemisphere towards our star, providing more heat and light and marking the start of astronomical summer.ĭespite these shorter nights, there are many wonderful sights to look out for this month. The summer solstice falls on 21 June, bringing the longest day and shortest night of the year.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |