The Winter Solstice

A solstice is an astronomical event that occurs twice a year, when the tilt of the Earth’s axis is pointed toward or away from the Sun, causing the Sun to reach its northernmost or southernmost extreme. The name is derived from the Latin sol (sun) and sistere (to stand still), because at the solstices, the Sun stands still in declination; that is, its apparent movement north or south comes to a standstill. This years winter solstice happens on the 21st December at 12.04.

The closest full moon for 15 years

The Moon is set to pass closer to the Earth tonight evening than it has done for the past 15 years. The Moon’s elliptical orbit means its distance from the earth is not constant and this varying distance can make the moon appear brighter and larger in the sky at certain times during its orbit.

The Moon is usually about 385,000km from Earth, but tonight it will be closer at around 363,000km.

Friday’s full moon could appear up to 14% bigger and 30% brighter than other full moons this year, a spokesperson at NASA said.

“Its only every few years that a full moon happens to coincide with the part of the Moon’s orbit when its closest to the Earth,” said Marek Kukula, an astronomer at the UK’s Royal Observatory.

“What people will see is a full moon that’s really bright and a bit bigger than what they’re used to.”

It will appear largest as it rises and sets, but this is a psychological illusion, Dr Kukula said.

“When it’s close to the horizon, our brain interprets it as being bigger than it actually is, this is called the moon illusion,” he said.

“The size may be striking when it’s near the horizon,” said Robert Massey of the UK Royal Astronomical Society. However, he cautioned against expecting too much.

“The Moon may be brighter and may appear somewhat larger, but it’s really quite hard for the eye to notice the difference; the eye will compensate for the extra brightness, it’s not like going from night to day,” said Dr Massey.

The Moon’s brightness varies throughout its annual cycle, during the mid-winter in the northern hemisphere it can appear brighter simply because it is higher in the sky.

The Planets and Stars size comparison

We now know the order of sizes of the planets in our Solar System from tiny Pluto to giant Jupiter and even how Jupiter is dwarfed by our own sun. We also know that the sun is what we call a ‘dwarf’ star – it’s not particularly big by stellar standards, but how small is it? Well, it’s not the smallest star we know of – that honour falls to a star called OTS 44, a brown dwarf in the constellation Chamaeleon.

The Moon

In the final two weeks of the class, we are going over the Sun and the Moon. Last week, we marvelled at the reach and power of the Sun, how it works, how it behaves and what powers the immense fusion engine in its core. This week, a bit closer to home, is the Moon, our only natural satellite. Even though the Moon is over 380,000km away, it is actually closer to us than most of you know.

Venus and Jupiter and…

the Moon! Tonight only (1st December), something wonderful will happen in the sky – a Lunar Occulation of Venus…