Spectacular Saturn Transit

19 02 2009

Something is about to happen on Saturn that’s so pretty, even Hubble will pause to take a look.

“On Feb. 24th, there’s going to be a quadruple transit of Saturn’s moons,” says Keith Noll of the Hubble Space Telescope Science Institute. “Titan, Mimas, Dione and Enceladus will pass directly in front of Saturn and we’ll see their silhouettes crossing Saturn’s cloudtops—all four at the same time.”

Hubble won’t be the only one looking. Amateur astronomers will be able to see it, too.

Transits like these are rare. “They only happen every 14 to 15 years when the orbits of Saturn’s moons are nearly edge-on to Earth,” says Noll. In 1995-96, the last time the geometry was right, Hubble photographed two (Titan and Tethys) and three (Mimas, Enceladus, Dione) moons transiting Saturn. This will be the first time the great telescope captures four.
The event begins on Tuesday morning, Feb. 24th at 10:54 UT when Titan’s circular shadow falls across Saturn’s cloudtops. About forty minutes later, the ruddy disk of Titan itself moves over the clouds.

“Titan is so big, you can see it just by looking through the eyepiece of a small telescope—no special camera is required,” says Go.

One by one, the smaller moons Mimas, Dione and Enceladus will follow Titan. At 14:24 UT, all four satellites and their shadows will simultaneously dot Saturn’s disk.

Titan transits Saturn on Feb. 8, 2009. (Christopher Go, the Philippines)
Titan transits Saturn on Feb. 8, 2009. (Christopher Go, the Philippines)
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In Saturns Shadow

11 02 2009

After successfully observing Venus, the Moon and Saturn (with tiny Titan) last night, I thought it was apt to show you this impressive panorama of Saturn, taken by the Cassini probe, currently in orbit around the ringed planet. Read the rest of this entry »





Eclipses

27 01 2009

An eclipse (from the Greek ekleipô, “to vanish”) is an astronomical event that occurs when one celestial object moves into the shadow of another. The term is most often used to describe either a solar eclipse, when the Moon’s shadow crosses Earth’s surface, or a lunar eclipse, when the Moon moves into the shadow of Earth. However, it can also refer to such events beyond the Earth-Moon system: for example, a planet moving into the shadow cast by one of its moons, a moon passing into the shadow cast by its parent planet, or a moon passing into the shadow of another moon. An eclipse is a type of syzygy (a line up of astronomical bodies), as are transits and occultations. Eclipses are impossible on Mercury and Venus, which have no moons. Read the rest of this entry »





The closest full moon for 15 years

12 12 2008

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. Read the rest of this entry »





The Planets and Stars size comparison

8 12 2008

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. Read the rest of this entry »





The Moon

1 12 2008

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.
Read the rest of this entry »





Venus and Jupiter and…

1 12 2008

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