Astroblog: Guided by the Light; Using the Moon to find the Bright Planets

Sunday, January 13, 2013

Guided by the Light; Using the Moon to find the Bright Planets


Jupiter, Aldebaran and the Moon as seen from Adelaide, Australia on January 22, 2013 at 10 pm local daylight saving time, looking north. Similar views will be seen from the Southern hemisphere. The Moon's size has been exaggerated for ease of viewing (click on any image to embiggen).	Jupiter, Aldebaran and the Moon as seen from Roswell, New Mexico on January 21, 2013 at 10 pm local time, looking South near the zenith. Similar views will be seen from the Northern hemisphere. The Moon's size has been exaggerated for ease of viewing (it looks like the Moon is covering Jupiter, but it doesn't).

Finding the bright planets (Mercury, Venus, Mars, Jupiter and Saturn) should be relatively easy as they are, well, bright. But as a beginner, how do you tell them from all the bright stars in the sky? Most newspapers publish rise set times for planets, but from there you can only work out the general area in the sky they will be. A good guide is that, in general, stars twinkle and planets don't. But on a still night this doesn't help (and there is a lot of sky to scan.

You can buy any number of sky charts, but they can be confusing to start off with when you are still a little unfamiliar with the sky, and the star formations are unfamiliar (by the way, I use Stellarium, a free photo-realistic sky planetarium program, it's fantastic for sky gazing. A guide to using Stellarium and some of the cool things it can do is here).

So what is a REALLY recognisable object, that is easy to find, and is close to the planets sometimes? The Moon of course. The Moon comes close to each of the bright planets at least once a month, so if you can identify the Moon, then if you know when the Moon and the bright planets are close, then it's a cinch. As well, the Moon and bright planets can form really lovely patterns in the sky.

But, of course, you need to have a list of times when the Moon is close to the bright planets. Luckily, I have one here. Of course, it is set up for Australia. As Australia is 8-10 hours ahead of Universal Time, for places behind UT (like the Americas) the occurrence will be the day before.

As an example, in about a weeks time on the 22nd of January in Australia, the Moon will be close to the planet Jupiter (see the diagram above) and make a nice formation with Jupiter and the bright star Aldebaran. For the America's this event will take place on the 21st (with the Moon really close to Jupiter). The presence of Aldebaran may be confusing, but it is a red star, while Jupiter will be a golden yellow, and the brighter of the two. Generally, the brightest object closest the Moon is the planet (Mars far from opposition is the exception).

Similarly, on February 4th in Australia, the Moon is close to Saturn, people in the Americas will see this on the 3rd, their time (see below).

People in the northern hemisphere will have a reversed view from those in the southern hemisphere, but in terms of finding things close to the Moon, this doesn't matter.

After you have identified the planets with the Moon, you can use this knowledge to spot them on subsequent nights. Of course, the planets move, but slowly, so shortly you can become familiar enough with the sky to locate them with ease.

Only Jupiter, Saturn and Venus are visible at the moment, Mars and Mercury are hidden by the Sun. However, over the coming mnths there will be several good planet/Moon enocunters, so it is worth looking out for them.


Saturn and the Moon as seen from Adelaide, Australia on February 4, 2013 at 3 am local daylight saving time, looking east. Similar views will be seen from the Southern hemisphere. The Moon's size has been exaggerated for ease of viewing.	Saturn and the Moon as seen from Roswell, New Mexico on February 3, 2013 at 3 am local time, looking East. Similar views will be seen from the Northern hemisphere. The Moon's size has been exaggerated for ease of viewing.