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Voyager – the journey continues

AFTER 33 YEARS, NASA’s twin Voyager spacecraft are still going strong and still sending home information. This video features highlights of the Voyager journeys to the outer planets, and looks at their current status, at the edge of our Solar System, poised to cross over into interstellar space.

Adapted from information issued by NASA / JPL.

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Planets all in a row

EARLY-RISING AUSTRALASIAN SKYWATCHERS are in for a treat this coming Saturday morning, April 30, as four of the naked-eye planets and the crescent Moon all come together in the morning sky before dawn.

In the video above, Melbourne Planetarium’s marvellous astronomer, Tanya Hill, explains when and where to see the spectacle.

And you can keep up-to-date with sky happenings with SpaceInfo.com.au’s monthly Whats’ Up? section.

Video courtesy of Museum Victoria.

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Uranus fly-by – 25 years ago today

True- and false-colour images of Uranus

Two views of Uranus—one in true colour (left) and the other in false colour—were compiled from images returned Jan. 17, 1986, by the narrow-angle camera of Voyager 2. The spacecraft was 9.1 million kilometres from the planet, and several days from closest approach.

AS NASA’S VOYAGER 2 spacecraft made the only close approach to date of our mysterious seventh planet Uranus 25 years ago, Project Scientist Ed Stone and the Voyager team gathered at NASA’s Jet Propulsion Laboratory, Pasadena, California, to pore over the data coming in.

Images of the small, icy Uranus moon Miranda were particularly surprising. Since small moons tend to cool and freeze over rapidly after their formation, scientists had expected a boring, ancient surface, pockmarked by crater-upon-weathered-crater.

Instead they saw grooved terrain with linear valleys and ridges cutting through the older terrain and sometimes coming together in chevron shapes. They also saw dramatic fault scarps, or cliffs. All of this indicated that periods of tectonic and thermal activity had rocked Miranda’s surface in the past.

Surface of Miranda

A section of the surface of Miranda, innermost of Uranus' large satellites, as seen by Voyager 2 from 36,000 kilometres away. A complex topography of high and low terrain, craters and scarps can be seen.

The scientists were also shocked by data showing that Uranus’s magnetic north and south poles were not closely aligned with the north-south axis of the planet’s rotation. Instead, the planet’s magnetic field poles were closer to the Uranian equator. This suggested that the material flows in the planet’s interior that are generating the magnetic field are closer to the surface of Uranus than the flows inside Earth, Jupiter and Saturn are to their respective surfaces.

“Voyager 2’s visit to Uranus expanded our knowledge of the unexpected diversity of bodies that share the solar system with Earth,” said Stone, who is based at the California Institute of Technology in Pasadena. “Even though similar in many ways, the worlds we encounter can still surprise us.”

Here’s NASA’s pre-encounter video from the 1980s, showing how Voyager 2 sped past the planet while collecting its data:

A host of new discoveries

Voyager 2 was launched on August 20, 1977, 16 days before its twin, Voyager 1. After completing its prime mission of flying by Jupiter and Saturn, Voyager 2 was sent on the right flight path to visit Uranus, which is about 3 billion kilometres away from the Sun. Voyager 2 made its closest approach—within 81,500 kilometres of the Uranian cloud tops—on January 24, 1986.

Before Voyager 2’s visit, scientists had to learn about Uranus by using Earth-based and airborne telescopes. By observing dips in starlight as a star passed behind Uranus, scientists knew Uranus had nine narrow rings.

But it wasn’t until the Voyager 2 flyby that scientists were able to capture for the first time images of the rings and the tiny shepherding moons that sculpted them. Unlike Saturn’s icy rings, they found Uranus’ rings to be dark grey, reflecting only a few percent of the incident sunlight.

Voyager image of Uranus' rings and two moons

Voyager 2 discovered two "shepherd" moons associated with Uranus' thin rings.

Scientists had also determined an average temperature for Uranus—minus 214 degrees Celsius—before this encounter, but the distribution of that temperature came as a surprise. Voyager showed there was heat transport from pole to pole in Uranus’ atmosphere that maintained the same temperature at both poles, even though the Sun was shining directly for decades on one pole and not the other.

By the end of the Uranus encounter and science analysis, data from Voyager 2 enabled the discovery of 11 new moons and two new rings, and generated dozens of science papers about the quirky seventh planet.

Interstellar mission

Voyager 2 moved on to explore Neptune, the last planetary target, in August 1989. It is now hurtling toward interstellar space, which is the space between stars. It is about 14 billion kilometres away from the Sun.

Voyager 1, which explored only Jupiter and Saturn before heading on a faster track toward interstellar space, is about 17 billion kilometres away from the Sun.

“The Uranus encounter was one of a kind,” said Suzanne Dodd, Voyager project manager, based at JPL. “Voyager 2 was healthy and durable enough to make it to Uranus and then to Neptune.”

“Currently both Voyager spacecraft are on the cusp of leaving the Sun’s sphere of influence and once again blazing a trail of scientific discovery.”

The Voyagers were built by NASA’s Jet Propulsion Laboratory in Pasadena, California, which continues to operate both spacecraft.

Link: More information about the Voyager spacecraft

Adapted from information issued by NASA Jet Propulsion Laboratory.

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What’s up? November’s night sky

Amateur telescopes pointed at the sky

November is a good month for stargazing. If you have a telescope or binoculars, great—but don't worry if you haven't, as all of the phenomena described below can be seen with the unaided eye.

The planets Venus and Saturn make a welcome re-appearance this month, out to the east in the morning sky. You won’t miss Venus—it’s the biggest and brightest light in sky (after the Sun and Moon, of course). Saturn will be to the north of Venus.

Mars is still in the western sky, low on the horizon after sunset and getting lower with each passing day. Mercury is doing the opposite—it is low on the western horizon after sunset but rising higher each night. It will appear close to Mars in the second half of the month.

The giant planet Jupiter is high and bright in the northern sky during November evenings. If you have a telescope and know exactly where to look, you’ll be able to spot the seventh planet, Uranus, nearby to Jupiter. Unfortunately, for most observers it is too dim to be seen with the naked eye.

The Leonid meteor shower will make its once-a-year appearance again this month, with the possibility of meteors being seen over about a one-week span in the middle of the month. The best date to try and see them will the 18th.

Except where indicated, all of the phenomena described here can be seen with just the unaided eye.

Dates and times shown here are for the Australian Eastern Daylight Time zone, and sky directions are from the point of view of an observer in the Southern Hemisphere.

Amateur telescopes pointed at the sky

An astronomy club is a great place to learn more about the night sky. Check out the list of clubs by clicking on the Links button at the top of the page.

November 4

The Moon will be at perigee today, which is the closest point in its orbit around the Earth. The distance between Earth and Moon will be 364,189 kilometres.

November 6

It’s New Moon today.

November 7

The thin crescent Moon will appear close to Mercury. You might have difficulty seeing them if there are buildings, trees, hills etc in the way. Assuming you do have a clear horizon, you might even need a pair of binoculars to spot them, as they’ll be very low on the western horizon.

November 8

Watch for the Moon next to Mars.

November 14

It’s First Quarter Moon today, which is halfway between New Moon and Full Moon. And take a look into the western sky after sunset, and low down near the horizon you’ll see Mars next to the red supergiant stars Antares in the constellation Scorpius. Compare the colour and brightness of Mars and Antares—Antares means “rival of Mars”.

November 15

The Moon will be at apogee today, which is the farthest point in its orbit around the Earth. The distance between Earth and Moon will be 404,634 kilometres.

November 16

Watch for the Moon near to the giant planet Jupiter tonight, high in the northern half of the sky.

November 17

There’ll be an interesting grouping low in the western sky tonight after sunset, with Mercury sitting between Mars and Antares.

Meteor in the night sky

A meteor flashes across the night sky. The Leonid meteor shower is predicted to reach its annual maximum in the early morning hours of November 18.

November 18

The early hours of this morning will probably be your best bet to see some of the Leonid meteor shower meteors. You’ll have to be an early riser, as the best time to see them will be after 4:00am. Look to the north-east, about halfway up from the horizon. From a very dark location, you might expect to see about 20 meteors per hour. If you live in a light-polluted town or city, you can expect to see fewer.

Leonid meteors are pieces of tiny dust and debris left in the trail of a comet called Tempel-Tuttle (after its two discoverers). Floating through space, they run into Earth’s atmosphere at a huge speed (around 70 kilometres per second!), so it’s no wonder they put on a light show as they disintegrate in the upper atmosphere.

November 19

Watch for Mars and Mercury near to each other tonight, low down on the western horizon after sunset.

November 21

It’s Full Moon today. Have a look and see if you can see a faint star cluster near to the Moon. This is the Pleiades, or Seven Sisters, a pretty grouping of stars in the constellation Taurus.

November 29

It’s Last Quarter Moon today, which is halfway between Full Moon and New Moon. Take a look at the Moon, and nearby you’ll see a fairly bright, bluish-coloured star. This is Regulus, the brightest star in the constellation Leo.

If you have any questions or comments on the night sky, please use the feedback form below. Happy stargazing!

Images courtesy IAU.

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