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Mars will be at opposition on Christmas Eve


Mars at opposition

On 24th December, at 20:00 UT planet Mars will be situated at opposition, as observed from the Earth: it will be at the point of the sky diametrically opposed to the Sun, as can be seen in the next diagram:

Diagrama de la Terra i Mart en oposició: el Sol i Mart es troben sobre una mateixa línia, amb la Terra entre els dos.

Diagram of the Earth and Mars at opposition. It is not to scale.
Courtesy: NASA

This configuration is especially favorable for observation, because of different reasons: on the one hand, Mars is allways very bright at opposition, due to it is quite close to our planet at this point (this year, closest approximation takes place on 19th December). On the other hand, at opposition objects are visible through the whole night: they rise from behind the eastern horizon at the moment Sun is setting and doesn't set until sunrise.

Although the closest approximation of this year is quite less close than the ones of 2001, 2003 or 2005 and, consequently, the apparent size of Mars is quite smaller, the situation of the red planet is ideal for observation.

This is due to the fact that this year opposition takes place very close to the winter solstice (22nd December) and then Mars is nearly as high in the northern sky as it can be. The next diagram can help to understand this.

Digrama de la Terra i la volta celest, sobre la qual s'ha marcat el nord i dibuixat l'equador celest (tall de la volta celest pel pla perpendicular a la direcció sud-nord) i l'eclíptica (recorregut aparent del Sol sobre la volta celest en un any), els quals formen un angle de 23,5º, de manera que el Sol està 23,5º per sobre de l'equador en el solstici d'estiu, a sobre de l'equador en els equinoccis (punts de tall de l'eclíptica i l'equador celest) i 23,5º per sota de l'equador celest en el solstici d'hivern

Diagram of the celestial equator and the ecliptic. At opposition, Mars is situated nearly as high as possible if the Sun is close to the winter solstice.
Courtesy: Astronomynotes

When an object is so high above the horizon, the influence of the atmosphere on observation becomes minimum, because of the light from it must follow the shortest path through the atmosphere and so quality of astronomical images is greatly improved.

Full Moon on Christmas Eve will be an additional charm for observers. The night of 24th December, we will see the Moon rising from the eastern horizon at sunset close to a very bright planet Mars. Both will move together through the sky, arriving very high at the middle of the night, to finally set nearly at the time of sunrise.

The Moon will hide Mars when observing from some places

This extreme approximation of the Moon and Mars is, in fact, an occultation of the planet by our satellite when observing from a significant area of the northern hemisphere: Alaska and northwest of Canada, Iceland, Germany, Scandinavian countries, Eastern Europe, etc.

Plànol de les zones des d'on serà observable l'ocultació.

Map of the areas from where the occultation will be visible Courtesy: IOTA .

From these places, the Moon will hide Mars from observer's sight, as happened at the Iberian Peninsula with [[][ Saturn on 22nd May ]] and with [[][ Venus on 18th June ]]of this year 2007.

You will find more information on IOTA's site.

Opposition and closest approximation don't necessarily coincide

Probably, some of our readers find surprising that opposition and closest approximation of a given planet don't necessarily coincide, as could seem obvious from a first hurried analysis of a diagram like the following one:

Diagrames del moviment de la Terra i Mart entorn del Sol. Les òrbites semblen circulars, quan no ho són..

Diagram of the movement of the Earth and mars around the Sun on August and December 2007
Courtesy: NASA

It must be considered that planetary orbits aren't perfect circumferences. Actually, they are ellipses which are more or less similar - depending on each case - to a circumference:

Diagrama on es mostren les òrbites reals (el·líptiques) de Mercuri, la Terra i Mart, així com les òrbites ideals circulars amb radi igual a la distància mitjana de cada planeta al Sol. Mentre la Terra segueix una òrbita molt i molt circular, Mart i Mercuri s'allunyen significativament de la circularitat. S'observa, a més, que l'orientació de les diferents òrbites (entengui's, si es vol, dels seus respectius semieixos majors) no és la mateixa.

Diagram of the actual forms of planetary orbits compared with the ideal circumferences of radius equal to the average distance of each planet to the Sun.
Courtesy: NASA

This way, one can easily understand that the distance to a planet which is at closest approximation with respect to us isn't always the same (as would happen with circular orbits), but depends on the exact point of each orbit where each planet is. Moreover, this diagram helps to understand that closest approximation can happen before opposition - if Earth starts to move away from Mars before arriving to the latter -, after opposition - if our planet starts to move away after it - or simultaneously.

The flash animation you can find following this link will very likely help you to understand what we are trying to explain.

Your images

Take advantage ot the nearly unbeatable conditions we will enjoy if we have a clear sky to take images of the red planet and send them to us!


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