The Equation of Time
This is a table of the amount by which the Sun is fast or slow each day compared with the average time that we use for our everyday life – and which is why, for example, Greenwich Mean Time is the mean, or average, of the variations in solar time.

The reason this is necessary is that the Earth's orbit around the Sun is not a perfect circle but is an ellipse. When the Earth is comparatively close to the Sun (as it is in January), it moves faster in its orbit than when it is farther from the Sun, as in June.

As a result, when the Earth is moving faster than average in its orbit, the Earth doesn't rotate on its axis quite enough during one day to bring the Sun due south at 12 noon by our watches, and it is slow.

Here is a table giving the approximate dates when the Sun is fast(–) or slow (+) compared with your watch by a whole number of minutes:

Jan 1     3
Jan 3     4
Jan 5     5
Jan 8     6
Jan 10   7
Jan 12   8
Jan 15   9
Jan 18 10
Jan 2   11
Jan 2   12
Jan 29   13
Feb 5    14
Feb 26  13
Mar 4    12
Mar 8    11
Mar 2    10
Mar 16    9
Mar 19    8
Mar 22    7
Mar 26    6

Mar 29   5
Apr 1      4
Apr 5      3
Apr 8      2
Apr 12    1
Apr 16    0
Apr 21  –1
Apr 26  –2
May 3  – 3
Jun 3   – 2

Jun 9      –1
Jun 14    –0
Jun 19      1
Jun 24      2
Jun 29      3
Jul4         4
Jul 10       5
Jul 18       6
Aug 12     5
Aug 17     4

Aug 22     3
Aug 26     2
Aug 29     1
Sep 2       0
Sep 5     –1
Sep 8     –2
Sep 11   –3
Sep 14   –4
Sep 17   –5
Sep 20   –6

Sep 22  –7
Sep 25  –8
Sep 28  –9
Oct 1    –10
Oct 4    –11
Oct 8    –12
Oct 11  –13
Oct 15  –14
Oct 20  –15
Oct 27  –16

Nov 17  –15
Nov 22  –14
Nov 25  –13
Nov 28  –12
Dec 1    –11
Dec 4    –10
Dec 6      –9
Dec 8      –8
Dec 11    –7
Dec 13    –6

Dec 15    –5
Dec 17    –4
Dec 19    –3
Dec 21    –2
Dec 23    –1
Dec 25      0
Dec 28      1
Dec 30      2

How does this affect you? If you are trying to find your north-south line by day, make the correction to find out when the Sun is exactly on your meridian. For example, on 2 March the Sun is due south at 12.10 pm. Or if you have a well-made sundial, add or subtract the figures shown to get the local civil time. If the sundial reads 3.45 on 17 November, the time by your watch should be 3.30 pm. 

Actually, there are other factors affecting sundial time, of which the main one is shoddy manufacture, which is the problem with most of the sundials you buy in garden centres these days... but don't get me started, that's another story. With a well-made sundial, the other correction you must make is for your distance from the meridian of the time zone you are in. Even in a small country such as the UK this can be considerable. Remember that every 15º of longitude makes an hour ofdifference in the solar time, or 4 minutes per degree. So in Cornwall, west Wales, western Scotland or Northern Ireland you are about 5º west of the Greenwich meridian and the solar time is 20 minutes later than GMT. On 5 February in Belfast, therefore, a sundial will tell you that it is not noon until 12.35 on your watch, and in early August it will be 1.28 pm when the sundial reads noon, because of British Summer Time.

Once you have made these corrections, a properly made sundial should give you the time just as accurately as most digital watches, which can easily drift off by half a minute or more unless they are regularly checked.

For a full listing of the Equation of Time for every day in the year go to
http://freepages.pavilion.net/users/aghelyar/sundat.htm (separate site).
What's in the sky tonight?
Below is a listing of the visibility the bright planets for each year until 2020. But if you just want to know what the sky will look like tonight, where you are, try the website www.heavens-above.com.Once you have registered (free) with your own location you can get a whole-sky map (under Astronomy) and get your own predictions for bright satellites such as the International Space Station and the Iridium satellites which flare in brightness.

Positions of the planets
Mercury
The table below gives the dates on which Mercury is farthest from the Sun and therefore visible in either the evening or the morning sky. In each case the figure in degrees tells you how far it will be from the Sun. The planet will be visible for a week or two on either side of these dates, but it won't always be easy to see.
   From either hemisphere, Mercury is easiest to see when its evening appearance is in spring, but of course these months are different depending on which hemisphere you are in.
    Look about 45 minutes after sunset or before sunrise as appropriate, in the direction if the greatest twilight.
2013 July 30 Morning 20
2013 October 9 Evening 25
2013 November 18 Morning 19
2014 January 31 Evening 18
2014 March 14 Morning 28
2014 May 25 Evening 23
2014 July 13 Morning 21
2014 September 22 Evening 26
2014 November 2 Morning 19
2015 January 15 Evening 19
2015 February 25 Morning 27
2015 May 7 Evening 21
2015 June 25 Morning 22
2015 September 4 Evening 27
2015 October 16 Morning 18
2015 December 29 Evening 20
2016 February 7 Morning 26
2016 April 19 Evening 20
2016 June 5 Morning 24
2016 August 17 Evening 27
2016 September 29 Morning 18
2016 December 11 Evening 21
2017 January 19 Morning 24
2017 April 1 Evening 19
2017 May 18 Morning 26
2017 July 30 Evening 27
2017 September 12 Morning 18
2017 November 24 Evening 22
2018 January 2 Morning 23
2018 March 16 Evening 18
2018 April 30 Morning 27
2018 July 12 Evening 26
2018 August 27 Morning 18
2018 November 7 Evening 23
2018 December 15 Morning 21
2019 February 27 Evening 18
2019 April 12 Morning 28
2019 June 24 Evening 25
2019 August 10 Morning 19
2019 October 20 Evening 25
2019 November 28 Morning 20
2020 February 11 Evening 18
2020 March 24 Morning 28
2020 June 5 Evening 24
2020 July 23 Morning 20
2020 October 2 Evening 26
2020 November 11 Morning 19
Venus
Like the tables for Mercury, this table gives the date when Venus is farthest from the Sun. But unlike Mercury, Venus is visible for months, rather than days, on either side of the date shown. And it is also best seen in the evening skies when it appears in spring, or the morning skies when it appears in autumn.
2013 November 1 Evening
2014 March 23 Morning
2015 June 7 Evening
2015 October 26 Morning
2015 December 29 Evening
2017 January 13 Evening
2017 June 4 Morning
2018 August 17 Evening
2019 January 6 Morning
2020 August 13 Morning
Mars
Here are the dates of opposition for Mars – that is, the dates on which it is opposite the Sun in the sky, which is within a few days of its closest and brightest for the year. Also shown are the constellations in which it will be on those dates. It will be visible for some months beforehand, but in the morning sky and in a constellation to the east of the one shown. After the date of opposition it will stay in the sky for several more months, moving into a constellation to the west of the one shown.
2014 April 9 Virgo
2016 May 22 Scorpius
2018 July 27 Capricornus
2020 October 14 Pisces
Jupiter
As with Mars, this table tells you the date of opposition for each year, when the planet is best visible, and due south at midnight. But unlike Mars, it moves much more slowly, so it will remain in that constellation for months, only moving into the next one over the course of a year. So Jupiter is always visible at around the same time of year, and in roughly the same place, for years at a time.
2014 January 6 Gemini
2015 February 7 Cancer
2016 March 8 Leo
2017 April 8 Virgo
2018 May 9 Libra
2019 June 11 Ophiuchus
2020 July 14 Sagittarius
Saturn
Saturn moves even more slowly than Jupiter, so is always visible at around the same time of year, and in roughly the same place, for years at a time. This table tells you the date of opposition, but you can find it for months before in the morning sky and months after in the evening sky in the same constellation.
2013 April 28 Libra
2014 May 11 Libra
2015 May 23 Libra
2016 June 3 Ophiuchus
2017 June 15 Ophiuchus
2018 June 28 Ophiuchus
2019 July 10 Sagittarius
2020 July 21 Sagittarius

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