Of oppositions and blood moons

Mars at opposition: The bright disc towards the centre of this image, just above the horizon is Mars, as captured by photographer Jimmy Westlake
Mars at opposition: The bright orange disk towards the centre of this image, just above the horizon is Mars, as captured by photographer Jimmy Westlake (click for full size)

Regular readers of this blog know I have something of a passing interest in space exploration and astronomy. I’ve been covering the Mars Science Laboratory mission since its arrival on Mars, and have also covered other space / astronomy related events and occurrences.

In keeping with this, I thought I’d mention two astronomical events of some interest which occur over the next two weeks. Neither of them is exactly rare, but if you’re lucky enough to be in the Americas, you’ll get to enjoy both at the same time – and a little bit more.

The first of these is the upcoming opposition with Mars, the time at which the Red Planet is at its closest to Earth. Oppositions happen around once every 26 months, and are so-called because they mark the time when the Sun and Mars are on opposite sides of the Earth to one another. During periods of opposition, Mars can appear as one of the brightest objects in the night sky and can come within 100 million kilometres of Earth.

Mars on the 15th April at approx 02:00 BST / 03:00 CET (21:00 EDT of the 14th April), and making its closest approach to Earth in six and a half years, will be clearly visible in the constellation of Virgo, along with the Moon and Spica (image: ESA) – click for full size

This year, Mars will reach opposition with the Earth on Tuesday April 8th, when it, the Earth and the Sun will be aligned in an almost straight line. However, because of the nature of the orbits of the two planets, they will not reach their point of closest approach to one another until the night of Monday April 14th / Tuesday 15th, 2014. At that time, they’ll be just 92 million kilometres (57.5 million miles) apart – the closest their respective orbits have brought them to one another at opposition for six and a half years.

During April, Mars appears as a bright red “star” in the constellation of Virgo. At the period of opposition, it will be just above and to the right of the Moon, with Spica, the brightest start in Virgo, to the lower left of the Moon.

To mark this year’s opposition, NASA has produced a nice little video explaining matters some more.

As mentioned towards the top of this article, this year’s opposition is only half the story. This is because the night of closest approach is also the night of a total lunar eclipse which should be visible from almost all of North America and significant parts of South America, with the majority of USA in particular getting a front-row seat.

Things will get underway at around 23:00 PST (02:00 EDT) on the night of the  Monday 14th / Tuesday 15th April, when the Moon enters partial eclipse. Totality will be reached just after midnight PST (03:00 EDT). At this point those under the path of the eclipse should witness a “blood moon” in all its glory, flanked on either side by Spica and Mars.

A lunar eclipse "blood moon" seen Idaho, December 2011 (image: Matt Mills / Reuters)
A lunar eclipse “blood moon” seen Idaho, December 2011 (image: Matt Mills / Reuters) – click for full size

“Blood moon” is the term sometimes applied to a total eclipse as a result of the Moon appearing to turn orange-red in colour, the hue slowly intensifying as the eclipse progresses until it reaches a bloody colour during the period of totality (about an hour and a half), before fading once more. This change in colour is the result of the Sun’s light passing through the Earth’s atmosphere as our planet moves between the Sun and the Moon, and then shining on the face of the Moon. A paler colouration of this kind can also be seen across at least a part of the Moon’s face during a partial lunar eclipse.

A total lunar eclipse and the gradual change in the Moon’s colour as seen from Earth which sees total lunar eclipses sometimes referred to as “blood moons” – the result of sunlight passing through the Earth’s atmosphere and striking the Moon’s surface (animation: Wikipedia)

The eclipse is certainly something that should generate opportunities for some stunning photographs, particularly given the positions of Mars and Spica (itself the 15th brightest star  in the night sky, and a close binary star).

And that’s not all; April 15th actually marks the first of a total of four consecutive total lunar eclipses – referred to as a tetrad,  all of which can be observed from North America, and which occur at roughly 6 month intervals to one another, the rest being October 8th, 2014, April 4th, 2015 and the last on September 28th, 2015.

NASA has also produced a video on the upcoming eclipse and the phenomena known as tetrads.

Some have pointed to this tetrad as marking the start of the end times, because the phenomena are supposedly “rare”, and this particular one commences on Passover.

However, while there can be long periods of time between occurrences of tetrads, they can also pop-up relatively frequently. For example, this century will see a total of nine tetrads occur, the first having taken place in 2003/4. Nor is the fact that the upcoming tetrad occurs on Passover particularly unusual; there have been eight tetrads so far coinciding with Passover since the first century AD.

So, if you’re in a position to be able to do so on the night of the 14th / 15th April, ignore the doom merchants and go outside and enjoy the night sky view!