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Monthly Skywatchers' Page

For London and the UK

The Sun and eight major planets (plus KBO Pluto) to scale. Earth is third planet from the left.

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Introduction

The location of the stars and can be learnt throughout a single year from a book. Each month of the year, the same stars are visible from a given location. Different stars and constellations are visible as the year progresses. For example, in London, the constellation of Orion is always visible in the evenings of winter months of January and February. Scorpius is visible in the summer months of June and July around midnight.

The planets resemble stars except that, generally, they do not twinkle. Unlike the stars whose patterns are fixed, planets wander through the sky changing their positions amongst the starry background. This means that their periods of visibility change as the relative position of the Earth, Sun and planet vary. In one year Mars may be visible in August at midnight. In another year it may be behind the Sun and invisible from Earth during August.

This page gives the details of visibility for the five naked eye planets: Mercury, Venus, Mars, Jupiter and Saturn. It also gives information about comets, meteor showers and non-regular phenomena like eclipses, transits and occultations.

The Observers' Glossary explains the terms used. Alternatively run the mouse cursor over terms in maroon.

The descriptions below are for viewers in the Northern Hemisphere, especially London and the United Kingdom.
The planetary information is valid for any location at the same or similar Latitude (51.5°N).
Note that a degree in the sky is twice the apparent diameter of the Moon.

All times on this page are London (UK) times. This is normally GMT (Greenwich Mean Time also known as Universal Time).
In the United Kingdom, the clocks go forward by one hour for British Summer Time (BST) between mid March and late October.
A 24 hour clock is used so that 7pm is written 19:00.

July 2010

Mercury

Mercury is too close to the Sun to be visible in July.

Venus

Venus continues to be visible in the evening twilight setting two hours after the Sun at the beginning of July. During the month the planet continues to get lower in the sky and sets earlier. By the end of the month Venus will be setting just an hour and a half after the Sun.

Around 10th, the planet will be close to the star, Regulus, but binoculars will be needed to see this conjunction in the late twilight.

The thin crescent Moon joins Venus on 15th.

Mars

Mars is theoretically still an evening object. However, the bright twilights and the planet's faintness mean that the Mars is now effectively lost in the evening twilight.

On 16th, the planet will be above the crescent Moon and it may be found with binoculars.

Jupiter

Jupiter rises at midnight at the beginning of July. By the end of the month, the planet is rising by around 10pm.

The planet is close to the Moon on 4th and again on 31st.

With Venus beginning to disappear, Jupiter will be July's easiest to see planet.

Saturn

Saturn is visible in the evening sky and sets around midnight.

During the month Saturn and Mars get closer together and both planets disappear into the twilight by the middle of the month. On 16th both Saturn and Mars are close to the crescent Moon but binoculars will be needed to make this out.

The Sun

After the Solstice on 21 June, the Sun is now beginning to move south. This causes the days to get shorter, slowly at first. On 1st July the length of day is 16 hours 33 minutes. This decreases to 15 hours 27 minutes by the end of July.

At midnight on 5-6 July the Earth will be at its furthest from the Sun (Aphelion). The Earth's motion around the Sun is then at its slowest. This is one of the reasons why the times of sunrise and sunset are asymmetrical.

At aphelion, the Sun's distance from the Earth is 152.5 million km (as compared to 147.5 million km in early January). This is a difference of some 5 million km. The further Sun gives the Northern Hemisphere summer 7% less heat than it would otherwise receive from the Sun. The Sun's distance from the Earth does not cause the seasons. These are caused by the Earth's axis being tilted at an angle of 23.5° to the plane of its orbit around the Sun. It is this that causes both the length of the day and the noon day altitude of the Sun to vary throughout the year. It also causes the seasons to be reversed in the Southern Hemisphere.

The Sun enters Cancer on 20th.

Note that this date does not tie in with astrology as astrologers are using dates from two thousand years ago.

Date	Sunrise	Midday	Sunset	Length of Day	Sun's Noon Altitude	Notes
01-Jul	04:47	13:04	21:21	16h 33m	61.6°
02-Jul	04:48	13:05	21:20	16h 32m	61.5°
03-Jul	04:49	13:05	21:20	16h 31m	61.5°
04-Jul	04:50	13:05	21:20	16h 29m	61.4°	Morning Half Moon - Moon close to Jupiter
05-Jul	04:50	13:05	21:19	16h 28m	61.3°
06-Jul	04:51	13:05	21:19	16h 27m	61.2°	Earth furthest from the Sun (aphelion)
07-Jul	04:52	13:05	21:18	16h 25m	61.1°
08-Jul	04:53	13:06	21:17	16h 24m	61.0°
09-Jul	04:54	13:06	21:17	16h 22m	60.8°
10-Jul	04:55	13:06	21:16	16h 20m	60.7°
11-Jul	04:56	13:06	21:15	16h 18m	60.6°	New Moon - Total Eclipse of the Sun
12-Jul	04:57	13:06	21:14	16h 16m	60.4°
13-Jul	04:58	13:06	21:13	16h 14m	60.3°
14-Jul	05:00	13:06	21:12	16h 12m	60.2°
15-Jul	05:01	13:06	21:11	16h 10m	60.0°	Moon close to Venus
16-Jul	05:02	13:07	21:10	16h 08m	59.8°	Moon close to Mars and Saturn
17-Jul	05:03	13:07	21:09	16h 06m	59.7°
18-Jul	05:04	13:07	21:08	16h 03m	59.5°	Evening Half Moon
19-Jul	05:06	13:07	21:07	16h 01m	59.3°
20-Jul	05:07	13:07	21:06	15h 58m	59.1°	Sun enters Cancer
21-Jul	05:08	13:07	21:05	15h 56m	58.9°
22-Jul	05:10	13:07	21:03	15h 53m	58.7°
23-Jul	05:11	13:07	21:02	15h 51m	58.5°
24-Jul	05:12	13:07	21:01	15h 48m	58.3°
25-Jul	05:14	13:07	20:59	15h 45m	58.1°
26-Jul	05:15	13:07	20:58	15h 42m	57.9°	Full Moon
27-Jul	05:17	13:07	20:56	15h 39m	57.7°
28-Jul	05:18	13:07	20:55	15h 37m	57.4°
29-Jul	05:19	13:07	20:53	15h 34m	57.2°
30-Jul	05:21	13:07	20:52	15h 30m	57.0°
31-Jul	05:22	13:07	20:50	15h 27m	56.7°	Moon close to Jupiter

The Moon

Date	Notes
3	Apogee (Moon at its furthest from Earth, 405,036km)
4	Half Moon
4	Moon close to Jupiter
11	New Moon - Total Eclipse of the Sun
13	Perigee (Moon at its nearest to Earth, 361,116km)
15	Moon close to Venus
16	Moon close to Mars
16	Moon close to Saturn
18	Half Moon
26	Full Moon
29	Apogee (Moon at its furthest from Earth, 405,953km)

Solar Eclipse

On 11 July 2010, a Total Eclipse of the Sun will occur. The maximum duration of totality will be 5m 20s making this one of the longer solar eclipses. No part of this eclipse will be visible from anywhere in the UK.

Eclipses of the Sun occur when the Moon - in its monthly orbit around the Earth - passes between the Earth and the Sun. This can only happen at New Moon. The Moon's shadow (or umbra) passes across the Earth and any observer that finds themselves within it will experience a Total Eclipse of the Sun. The umbra is quite narrow, rarely more than a couple of hundred kilometres wide. Observers in the much wider penumbra will see a partial eclipse. Outside of the umbra or penumbra, no eclipse is visible.

During a Total Eclipse, the Sun is slowly covered by the Moon until it is completely hidden behind the Moon. The covering takes between an hour and a hour and a half and is called the Partial Phase. Looking at the Sun during a partial eclipse can only be done with special glasses - it is then possible to see the "bite" taken out of the Sun by the encroaching Moon.

The early part of the partial eclipse is not noticeable in terms of changes to the surroundings. Towards the end of the partial phase, the light takes on a strange quality and the sky turns an intense blue. Winds might change and the temperature may fall significantly. Animals and birds begin to behave strangely, the latter flying around looking for a place to roost. Venus may become visible as a white dot in the sky.

When the Sun is completely covered, Totality begins and the sky darkens rapidly. The light fades from day to a very late twilight in just a few seconds, an eerie effect that disorientates those experiencing it for the first time.

During totality, the sky becomes dark enough for stars and planets to be visible. Filters can be put down as the "Sun" can now be viewed with the naked eye. Along the horizon, the red colour of sunset is visible all around. Bird song or insect chirping can often be heard.

Looking up at the Sun, the Sun's magnificent CORONA is now visible, a pearly white delicate structure often marked with lines of the Sun's magnetic field. Sometimes red flames (called PROMINANCES) can be seen next to the Moon's jet black body - these are explosions of the Sun's surface which are not normally visible.

Totality is one of nature's great natural phenomena but is over all too quickly, lasting only a few minutes. But oh, what a few minutes...

When Totality ends, the sky brightens rapidly. Often the first piece of sunlight to return will pass through a lunar valley as the Moon is quite a rough body - not smooth like a billiard ball. This point of light is called the Diamond Ring and is normally very spectacular. The eclipse continues with another partial phase as the Moon moves away from the Sun. Finally the eclipse is over.

Unfortunately for people wishing to observe this eclipse, the path of totality passes almost exclusively over the Pacific Ocean making landfall on Mangaia (Cook Islands), Easter Island (Isla de Pascua) and a few isolated atolls in French Polynesia. The path ends in isolated regions of Chile and Argentina where weather conditions are not good, infrastructure and facilities are minimal, and the eclipse occurs while the Sun is setting.

The path of this eclipse can be found at the NASA Eclipse web site.

Total eclipses of the Sun occur roughly seven or eight times every decade but the area they cover is minute compared to the size of the Earth. On average, they happen in one location once every 400 years or so. For example, in London: the last time totality occurred in the UK capital was on 3 May 1715. The next totality in the city will be on 14 June 2151. This is a gap of 436 years. This is why most people never see a Total Eclipse of the Sun. To experience this phenomenon it is necessary to travel, unless you are very lucky.

The maximum theoretical duration for a Total Solar Eclipse is 7m 31s. Eclipses over 7 minutes are very rare.

Total eclipses of the Sun are very spectacular. People who are seeing one for the first time usually have one question to ask afterwards. When is the next one? The answer is 13 November 2012, 29 months later. This will be visible in North East Australia.

One final eclipse story:

On 28 May 585 BC, Cyaxares of Media (modern Iran) and Alyattes of Lydia (modern Turkey) were about to start a battle when a total eclipse of the Sun occurred. The two nations were so frightened that they signed a peace treaty. Because eclipses can be predicted very accurately by astronomers, this remains the earliest historical event that can be dated to the exact day.

Photos from my previous total eclipses of the Sun.

Next Month

Venus in the evening sky, Jupiter in the morning sky. Meteor Shower.

All times on this page are London (UK) times.

Sources: Astronomy Now magazine, Cybersky, USA Naval Observatory and UK Nautical Almanac Office.

Books From Amazon.co.uk

Observers' Glossary

The Observers' Glossary

An explanation of the terms used by sky observers. Includes descriptions of how the objects of the solar system behave in the sky as seen from Earth (especially the Northern Hemisphere high latitudes).

KryssTal Related Pages

The Solar System

Tables and data about the Sun, Earth, Moon, planets, asteroids and comets. All terms used are explained.

Measuring The Stars

An account of how various properties of stars can be measured by studying starlight. Includes brightness, distance, luminosity, temperature, mass, radius, density and an introduction to the H-R Diagram.

The Brightest Stars

A table containing a list of the 20 brightest stars in the Earth's sky. Explanations of all the associated terms like magnitude, spectral type and radial velocity.

Eclipses, Transits and Occultations

A detailed account about eclipses, transits and occultations. These are irregular phenomena that can be observed in the sky. Includes eclipse trips around the world with photos and well as photos of recent transists of Mercury and Venus.

The Scale of the Universe

In astronomy distances and times are confusing because of the large numbers of zeros in the figures. This is an easy-to-understand scaling of the Universe in both space and time. Distances in space are represented by the time light takes to travel there. The chronology of the Universe is compared to a real year.

A Brief History of Astronomy

How humanity came from believing Creation Myths to postulating the Inflationary Big Bang Theory. The key stages in our understanding of our place in the cosmos and the people who broadened our understanding.

The Calendar

What do we mean by the words day, week, month, year? Who invented our calendar? When did the third millennium begin? The relation between time and astronomy.

Gravity

The force that moves apples and planets. A short introduction to the ideas of Kepler and Newton that culminated with the theory of Universal Gravitation.

Spherical Trigonometry

A look at the mathematics of a sphere with a section on sundials and the equation of time.

External Skywatching Links

These links will open in a separate window

StarDate Online
An excellent online skywatchers' magazine featuring detailed monthly information about astronomical events.

Astronomy Picture of the Day
A different image each day with an extensive archive and explanations.

Society for Popular Astronomy
Monthly planet and star gazing details with maps for young people.

Telescope House
A London based source of astronomical equipment, telescopes, software, maps and books.

Southern Sky Watch
Sky watchers information for the southern hemisphere.

Starry Night Pro
Superb planetarium software. Simulate the sky from anywhere on the Earth and any time.