Graphic: January night sky

MERCURY is at superior conjunction on the 7th and in the last week of January it reaches -1.0 magnitude and should be visible low in the southwest, setting 1.5 hours after the Sun. Much brighter Venus will be above Mercury. Venus is a brilliant -3.9 magnitude evening star, setting an hour after the Sun on the 1st and 2h after by the 31st. In bright twilight early in the month it will be seen in a dark sky by the end of January. Moon only 37 hours old close below on the 20th. Mars will remain in morning twilight until early June rising only 1.5h before the Sun throughout this period.

Jupiter is in Ophiuchus at -1.8 magnitude, rising by 04h by the 31st.

Jupiter is 5° above Antares early in the month. Waning crescent Moon below on the 15th. Saturn is in Leo at 0.0 magnitude and just west of Regulus. It rises soon after sunset by the 31st. Moon close by on the 6th. Uranus is in Aquarius setting about 19h 30m by the 31st. Moon nearby on the 22nd. Neptune is in Capricornus setting at sunset by the 31st. Moon nearby on the 20th.

The Moon: full 3d 14h, last quarter 11d 13h, new 19d 04h, first quarter 25d 23h. Moon near Regulus on the 6th, near Spica on the 11th and near Antares on the 15th. The Earth is at perihelion, its closest to the Sun (147 million km), on the 3rd.

London area, sunset: Jan 1 16h 00m, Jan 31 16h 45m, sunrise 08h 08m, 07h 40m. Nautical twilight ends: Jan 1 17h 20m, Jan 31 18h 05m, begins: 06h 45m, 06h 25m. Edinburgh area, sunset: Jan 1 15h 45m, Jan 31 16h 41m, sunrise: 08h 44m, 08h 10m.

Nautical twilight ends: Jan 1 17h 22m, Jan 31 18h 10m, begins: 07h 08m, 06h 40m.

The Quadrantids meteor shower has given strong displays in some years but in 2007 the Moon is full on the 3rd, the night of maximum activity, so conditions are unfavourable (see chart for radiant).

The start of a new year is a good time to look ahead to see which of the major planets Mercury to Neptune are well-placed for in the coming year and beyond. Uranus at 5.7 magnitude is visible to some naked eyes but picking it out from among many stars of similar brightness requires optical aid and a star chart. Neptune at 7.8 magnitude requires binoculars or a telescope. Both show very tiny discs which require a telescope magnifying 50 times or more. Uranus and Neptune have been known since 1781 and 1846 respectively.

This leaves the inner planets Mercury and Venus (with orbits inside that of the Earth) and the outer planets Mars, Jupiter and Saturn, all of which are easy naked-eye objects at some time or another.

The time a planet takes to orbit the Sun and return to the same direction relative to the stars is the sidereal period but of more relevance to their visibility is the synodic period, the time it takes for the Sun, Earth and planet to come into line (for the Earth and planet to have the same longitude). This determines when the inner planets reach inferior and superior conjunction (on the nearside and farside of the Sun) and the outer planets conjunction on the far side of the Sun and opposition, due south at midnight.

For Mercury the synodic period is 116 days so there are six apparitions each year, three morning and three evening. Of these two or sometimes three may be favourable for us in NW Europe. This year the best are in January-February and May-June in the evening and November in the morning.

For Venus the synodic period is 584 days (about 19 months) so we have two apparitions in 3 years 2 months. Generally there are two rather poor years followed by a very good one every fourth year, but no two periods are exactly alike. After last year when Venus was absent from the northern sky for much of the year, 2007 will be excellent. Venus will become visible in January, not setting in the northwest much before midnight in May and running into twilight in July. It reappears in the morning in September, rising as early as 02h in October and still 3h before the Sun by the year’s end.

Mars will rise before 0h in July and brighten steadily towards opposition in Gemini on the 24th December, when it will reach -1.7 magnitude. Jupiter is now far south of the equator in Ophiuchus all the year moving into Sagittarius in 2008. Having a period of 12 years, Jupiter spends 6 years in the southern hemisphere. Saturn completes an orbit of the Sun in 29.5 years and is now moving southwards through Leo. Most of us cannot expect to see Saturn high in the northern sky in Gemini more than three times in a lifetime.