Lutetia at closest approach

10 July 2010

The European Space Agencies (ESA) space probe Rosetta executed its flyby of asteroid Lutetia a few hours ago.

Here is the image taken at closest approach.

Lutetia’s name is derived from the Latin name for Paris. It is roughly 100 km large.

Rosetta is named after the Rosetta stone. Rosetta passed by asteroid Steins 5th September 2008.


Noctilucent clouds – revisited

9 July 2010

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.


21st June 2010 – Summer Solstice

20 June 2010

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.

The Sun photographed at the same time of day throughout the year

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.


22nd July 2009 – Eclipse third contact

11 August 2009

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.


20th March 2009 11:44 UTC – Vernal Equinox

20 March 2009

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).


14th March 1835 – Giovanni Schiaparelli born

14 March 2009

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”.

karte_mars_schiaparelli_mkl1888

Interestingly (or not) Google celebrates his birthday with this logo:
schiaparelli


13th March 1781 – Uranus discovery announced

13 March 2009

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.

Uranus

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.