Mars in the Night Sky

Mars is growing brighter in the sky, appearing close to the star Antares and the planet Saturn (see NASA image above). Later this month, Mars will reach the point of closest approach, and hence largest apparent size.

For the current distance to Mars, see Wolfram’s calculator or the live diagram of the solar system at Fourmilab, which includes images (green lines show orbits below the plane of the ecliptic):

Live Solar System image


WSC: Magellanic Clouds

I have previously posted about the spectacular night sky in the Australian Outback. Among other things, visitors from the Northern Hemisphere (as well as Southern city folk) will be able to see our companion galaxies, the Magellanic Clouds. The Magellanic Clouds are only visible well away from city or town lights. They can be seen at the top of the wonderful photograph below (taken in Chile, credit European Southern Observatory):


Venus and Jupiter in conjunction

The planets Venus and Jupiter were in conjunction last night, as the photograph above (by Neal Simpson) shows. The diagram below (by the Fourmilab) shows why: although Venus is much closer to Earth (and thus much brighter), the three planets are almost in a straight line. Venus and Jupiter should still be pretty close in the sky for the next few nights.

Four blood moons? Really?

In recent times, there has been a degree of interest – particularly within the USA – in so-called “blood moons” (as in the above book). Although this phrase is intended to recall Biblical texts such as Joel 3:21 (“The sun shall be turned to darkness, and the moon to blood, before the great and awesome day of the Lord comes”), it actually refers to ordinary lunar eclipses. Lunar eclipses are great to watch (see photo below), but are actually not particularly uncommon – see this list.

Much has been made of the “coincidence” of lunar eclipses occurring on major Jewish holidays. However, the geometry of lunar eclipses (see below) requires the moon to be on the opposite side of the earth from the sun, which means that lunar eclipses only occur on full moons. Furthermore, the Jewish calendar is a lunar one, so that several major holidays – such as Passover (15th of Nisan), Purim (in Jerusalem, 15th of Adar), and Sukkot (15th of Tishrei) – always occur on full moons. Lunar eclipses have therefore occurred on major Jewish holidays many times over the past two millennia.

Basically, the whole theory makes about as much sense as the panic of 2012. But, of course, that’s no reason not to watch the next lunar eclipse, on 8 October:

The analemma

If you photograph the sun at the same time every day (or every few days), you will find that the sun traces out a path in the sky, called the analemma. György Soponyai, in Budapest (Hungary), did exactly that at 8 AM each morning between 29 January last year and 6 January this year, to produce the wonderful photograph below (click to zoom):

More analemma photographs (by Anthony Ayiomamitis) can be found here. The shape of the analemma results from the fact that (1) the Earth is tilted on its axis by 23.5° and (2) the Earth orbits the sun in an ellipse, rather than a circle. The diagram below shows the calculated analemma for 12 noon at the Royal Observatory, Greenwich (latitude 51.48° N):

The concept of the analemma can also be used in constructing sundials. If an appropriate analemma is placed in the centre of the sundial, a gnomon placed at the right point on the analemma will correctly tell the time with its shadow (except for daylight-saving, of course).

Such sundials are popular in parks, because the viewer can stand on the analemma at a position corresponding to the current date, and his or her shadow will tell the time, without the need for additional time-of-year correction. I photographed the sundial above and below at Mt Stromlo Observatory in June 2012. It can be seen that the time was about 2:20 PM.

Mars gets closer and brighter…

On April 8, the planet Mars was in opposition. That is, Mars was on the opposite side of the sky to the Sun. Also, on April 14, Mars will be at the closest point to Earth in its orbit (92 million km). A great time to observe the “red planet”!

This video from Slooh explains various aspects of the planet at length:

For the current distance to Mars, see Wolfram’s calculator or the live diagram of the solar system at Fourmilab, which includes images (green lines show orbits below the plane of the ecliptic):

Live Solar System image