All five bright planets to align for the first time since 2005

[Carmen Elsa Irarragorri Wyland]

All five bright planets to align for the first time since 2005

All five planets visible with the naked eye will form a line across the night sky from tomorrow until February 20, for the first time since 2005.

Mercury, Venus, Mars, Jupiter and Saturn will be visible about an hour before sunrise, from high in the north to low in the east, according to Museum Victoria astronomer Dr Tanya Hill.

The remaining planets Neptune and Uranus and the dwarf planet Pluto are not visible with the naked eye, but Dr Hill said the five bright planets have been observed since ancient times.

"There are only a few amazing things in the night sky that can be seen without any equipment," Dr Alan Duffy from Swinburne University said.

There will be a viewing window between 5.30am and 5.40am (NZDT) on January 20, expanding to an hour between 5:00am and 6:00am February 20.

Dr Duffy suggested finding a clear horizon and a dark sky, which will be easiest outside cities, and to try on more than one morning to get the best view.

Dr Hill said Venus, Mars, Jupiter and Saturn have been visible together since the beginning of the year and will now be joined by Mercury, which is transitioning from an evening to a morning object.

"At first it will appear quite low to the eastern horizon and of all the planets it is also the faintest, so it will be hard to see to begin with," Dr Hill said.

"However, Mercury will continue to rise higher each morning and by early February it will sit just below bright Venus."

The order of the planets will not be the same as their order from the Sun.

Starting from the eastern horizon, Mercury (1) and Venus (2) will appear in order, then Saturn (6) followed by reddish Mars (4), with the solar system's largest planet, Jupiter (5) the last one in line.

The line formed by the planets closely follows the path of the sun across the sky, a line called the ecliptic, explained Dr Hill.

"This path marks the plane of our solar system, visual proof that the planets, including Earth, all orbit the Sun on roughly the same plane," she said.

However, each planet has a different yearly cycle, from Mercury's 88 Earth days to Saturn's 29.7 Earth years, so an alignment is reasonably rare and "essentially a quirk" of the universe, said Dr Duffy.

To help in identifying the planets, Dr Hill said the Moon will travel past each one in turn, beginning with Jupiter on January 28 and ending with Mercury on February 7.

The Moon will pass by Mars on February 1 and 2, Saturn on February 4 and Venus on February 6.

Dr Hill said the five planets will be together again in the evening sky in August, but then not until October 2018.