Lutetia’s name is derived from the Latin name for Paris. It is roughly 100 km large.
A couple of days ago we have had a fine sunset with noctilucent clouds.
So what is so interesting about noctilucent clouds?.
First of all they are clouds made of ice crystals that are extremely high up (75-85 km according to wikipedia). They can only be seen around twilight since they are then illuminated from underneath by the Sun that has already set. They are mostly seen from highish latitudes (50-70 degrees – I am at around sixty degrees). They are fairly uncommon.
Revisited because of my previous (failed) attempt to capture noctilucent clouds.
Today is the Summer Solstice.
What does this mean for regular folks? Well not much… Mostly it means that today is the longest day and at midday the Sun is as high in the sky as it gets during the year. In many countries this day marks the start of summer. Happy days…
Astronomically it is the day when the Earth’s axis tilt is most inclined towards the Sun. In the northern hemisphere this happens around the 20th or 21st of June and in the southern hemisphere around the 21st or 22nd of December.
In the image above (taken from APOD) the Sun is photographed at the same time of day throughout the year. The path it traces is called an analemma. Summer Solstice occurs on the day the Sun is at its highest. The figure of eight is caused because the Earth’s orbit is slightly elliptical and the Earth moves faster in its orbit when closer to the Sun. This means that in some parts of the year the Sun is further along in its path over the sky and at others it is behind.
Diamond ring at third contact. These images of the eclipse were taken from Tian Huang Ping, Anji, China.
This sequence took about 21 seconds in real time.
Today at 11:44 UTC (roughly the same as GMT).
The center of the Sun crosses the equatorial plane from south to north. On the equator the sun passes directly overhead. At the poles the Sun is on the horizon the whole day. On this day the Sun spends roughly the same length of time over and under the horizon so day and night are roughly equally long at all places on Earth.
Vernal equinox comes from the latin ver = spring, aequus = equal and nox = night (day and night of equal length).
Giovanni Schiaparelli was born on this day in 1835. He is perhaps best known because, as noted in Wikipedia:
he observed a dense network of linear structures on the surface of Mars which he called “canali” in Italian, meaning “channels” but mistranslated as “canals”.
From Wikipedia’s post on Uranus:
Sir William Herschel announced its discovery on March 13, 1781, expanding the known boundaries of the solar system for the first time in modern history. This was also the first discovery of a planet made using a telescope.
Sir William Herschel was not the first person to observe Uranus – John Flamsteed beat him to it. But Flamsteed did not recognise Uranus for what it was. The credit for the discovery therefore goes to Herschel.