Rising, transit and setting times and coming events.

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Today

A glossary of astronomical term may be useful and the following is not intended to be comprehensive. For now it is very small, but it will build up over time.

 

 

Noctilucent Clouds

'Night shining' clouds.

These are wispy clouds visible from high latitudes above the northern horizon for several weeks either side of the summer solstice. White or maybe electric blue in colour, they form in the highest regions of the atmosphere up to 100 km high, on the edge of space. They are made of water vapour but how they form is still controversial. Too tenuous to be seen in the daytime, they are visible in the late twilight light by the Sun below the horizon.

BBC audio slideshow

NASA Science News

 

 

Occultation

In astronomy, an occultation happens when one object passes in front of and obscures another. The Moon regularly occults stars as it orbits the earth, less frequently it occults planets. Very rarely a planet will occult another planet in the solar system.

Because the Moon is relatively close to the Earth a particular occultation may not be seen from all places, the star or planet may instead appear close to the Moon. Some places may witness a 'grazing occultation' when the star or planet skims the edge of the Moon, going in and out of view behind the lunar mountains.

 

Retrograde Motion

Jupiter begins ‘retrograde motion’ in early October. As the planets orbit the Sun they move against the background of stars. However the Earth also in motion and this changes our viewing point of any planet. Imagine Jupiter coming to a dead stop; it would still appear to drift back and forth against the stars over the course of a year because of our own planets motion. Add these two motions together and the superior planets (Mars outwards) trace loops in the sky rather than smooth orbital paths. Before opposition these planets appears to stop, then move retrograde (backwards). After opposition they again stop and continue with their direct motion.

Twilight: Astronomical

The period between the Sun being 12 and 18 degrees below the horizon.

Comes after evening and before morning nautical twilight. At the end of this all astronomical objects, including deep sky objects such as galaxies and nebulae, can be properly observed.

 

Twilight: Civil

The period between the Sun being 6 degrees below the horizon and sunrise or sunset.

In the evening it starts at sunset and ends when the centre of the Sun has sunk 6 degrees below the horizon. In the morning it starts when the centre of the Sun is 6 degrees below the horizon and ends at sunrise. During civil twilight the horizon is clearly visible and objects can be seen without extra illumination.

 

Twilight: Nautical

The period between the Sun being 6 and 12 degrees below the horizon.

Comes after evening and before morning civil twilight. At sea, navigation using the horizon as a reference is not possible because it is no longer visible. By the end of nautical twilight the sky is dark enough for many astronomical purposes.

 

 

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June Notes

Planets

 Mercury: Visible in the north-western twilight for first two weeks, setting 2 hours after the sun on June 1.
 Venus: Bright on the NW horizon but low down, setting 1½ hours after the sun all month.
 Mars: Very hard to locate in the morning twilight, will be easier in July.
 Jupiter: Conjunction behind the sun on June 19.
 Saturn: In the southern sky on Libra/Virgo border, fading to mag. 0.5 and setting 4½hours after sunset at end of June.

Venus is in the evening sky for several months now but will never be far above the western horizon, even at greatest elongation in November. It's brightness however makes it easy to see with an unobstructed view. For the whole of June Mercury is in the evening twilight with Venus. Having passed Venus in late May Mercury reaches greatest elongation on the 12th. It will pass Venus again as it moves towards the sun and disappears into the brightness by the month's end. Saturn meanwhile continues to share the south with Spica in Virgo.

Midnight Twilight

The summer solstice means that observation of neighbouring stars is pushed into late night and the early hours; the further north you go the lighter the nights will be. There is still plenty to see, just less time to see it. Low in the south is the red giant Antares in Scorpius, marking approximately the centre of our galaxy the Milky Way but never well seen from here. Lower on the northern horizon you can see Capella which a few months ago was overhead in the early spring evenings. The Summer Triangle marked by Vega, Deneb and Altair (in Lyra, Cygnus and Aquilla respectively) is rising in the east while Ursa Major and Bootes with the orange giant star Arcturus are in the west. The Milky Way gets higher as the night progresses, a good pair of binoculars will bring out the countless faint stars and nebulae.

Noctilucent Clouds

Noctilucent (‘night shining’) clouds can be seen in the late twilight in the months round the northern summer solstice. They are high (up to 100 km) tenuous clouds that can only be seen when the sun has set but still shines at these altitudes. Look in the northern sky at least an hour after sunset/before sunrise for thin, wispy bluish or white cloud formations. See featured video above.

CURRENT MOON

Featured Video: Noctilucent clouds (New)

NASA Sciencecast on the nature of noctilucent clouds.

Featured Video: Noctilucent clouds

Time lapse video giving a good idea of what noctlilucent clouds look like, always in the north (from UK latitudes) in the summer months.

Featured Video: Alcor and Mizar

Coming Events

Quote

Alvin Toffler

The next major explosion is going to be when genetics and computers come together. I'm talking about an organic computer - about biological substances that can function like a semiconductor.