Posted on by Fraser Cain

Gravity on Neptune

Neptune compared to Earth. Image credit: NASA

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Neptune is a gas planet, so it doesn’t have a solid surface. If you tried to walk on the surface of Neptune, you’d sink right in. But let’s say you could walk on Neptune. How strong is the gravity on Neptune? How heavy would you feel?

The surface gravity of Neptune is 1.14 times the gravity on Earth. In other words, if you could actually walk on Neptune, you would feel only a little heavier than if you were walking on Earth. If you weighed 100 kg on Earth, you would weight 114 kg on Neptune. Compare that to the much lower gravity you would feel on the Moon (16.5%) or Mars (37.6%).

Neptune has much more mass than Earth. In fact, it has a mass of 17 times the mass of the Earth. You would think that would make the gravity much more extreme. But it also has a much larger size. The diameter of Neptune is 3.8 times the diameter of Earth. This brings the gravity on Neptune down to a very comfortable 114% the gravity of Earth.

Except for the non-solid part, walking on Neptune would feel very comfortable.

Want to learn more about the gravity on the Moon, or the gravity on Mars?

If you’d like more information on Neptune, take a look at Hubblesite’s News Releases about Neptune, and here’s a link to NASA’s Solar System Exploration Guide to Neptune.

We have recorded an entire episode of Astronomy Cast just about Neptune. You can listen to it here, Episode 63: Neptune.

Posted on by Fraser Cain

How Far is Neptune from Earth?

Neptune, captured by Voyager 2. Image credit: NASA

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Here’s a quick answer: Neptune is approximately 4.4 billion km away from the Earth.

Have you ever wondered how far Neptune is from the Earth? It’s actually a bit of a trick question. That’s because the distance between Neptune and Earth is constantly changing, depending on where they are in their orbits around the Sun.

It gets even more complicated, because both Earth and Neptune follow the Sun on elliptical orbits. They both have a closest point to the Sun, called perihelion, and a distant point, called aphelion.

So, the closest point occurs when Earth and Neptune are on the same side of the Sun. Earth is at its most distant point from the Sun, and Neptune is at its closest. At this point, Earth and Neptune are separated by only 4.301 billion kilometers.

At their most distant point, Earth and Neptune are on opposite sides of the Sun, at the most distant points on their orbits. At this point, Earth and Neptune are separated by 4.553 billion kilometers.

If you’re interested, here’s an article that lists how far away all the planets are from the Sun and Earth.

If you’d like more information on Neptune, take a look at Hubblesite’s News Releases about Neptune, and here’s a link to NASA’s Solar System Exploration Guide to Neptune.

We have recorded an entire episode of Astronomy Cast just about Neptune. You can listen to it here, Episode 63: Neptune.

Posted on by Fraser Cain

Density of Neptune

Composition of Neptune. Credit: NASA

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The density of Neptune is 1.638 g/cm3.

Just to give you some comparison, the density of water is 1 g/sm3. In other words, if you had a bathtub big enough, Neptune would sink into it. This is different for Saturn which has a density of less than 1. While Neptune sinks, Saturn would float. Of course, both planets are much less dense than Earth, with a density of 5.51 g/cm3.

Want to calculate the density of Neptune on your own? It’s pretty simple math. Just take the mass of Neptune, and divide it by its volume.

The mass of Neptune is 1.0243×1026 kg, and the volume of Neptune is 6.254×1013 km3. Divide the two, and convert to grams per cubic centimeter, and you’ll get the density of Neptune: 1.638 g/cm3.

We have written many stories about Neptune on Universe Today. Here’s an article about how there might be liquid oceans deep within Neptune. And here’s an article with cool videos of Neptune captured by Hubble.

If you’d like more information on Neptune, take a look at Hubblesite’s News Releases about Neptune, and here’s a link to NASA’s Solar System Exploration Guide to Neptune.

We have recorded an entire episode of Astronomy Cast just about Neptune. You can listen to it here, Episode 63: Neptune.

Posted on by Tammy Plotner

Weekend SkyWatcher’s Forecast – November 28-30, 2008

Greetings, fellow SkyWatchers! Are you ready for a bit of a challenge this weekend? Then break out the big telescope and let’s go galaxy hunting in Cetus as we have a look at Hickson Compact Group 16. If you’d like to try something a little easier, then “monkey” around with planetary nebula, NGC 246! Got binoculars or a small scope? Then take on NGC 247 – it’s big, bright and beautiful! When ever you’re ready, I’ll see you out under the stars….

Friday, November 28, 2008 – Tonight in 1659, Christian Huygens was busy at the eyepiece – but he wasn’t studying Saturn. This was the first time any astronomer had seen dark markings on Mars! If Huygens and Herschel were alive to enjoy today’s new technology, you could bet they’d have a big backyard scope aimed about four degrees east of the Zeta-Chi pairing in Cetus to have a look at Hickson Compact Galaxy Group 16 (RA 02 09 31 Dec -10 08 59).

Consisting of four faint, small, galaxies designated as NGCs 835, 833, 838, and 839 clustered around a 9th magnitude star, these aren’t for average equipment – but are a true challenge for a seasoned observer. Groups of galaxies such as Hickson 16 are believed to be some of the very oldest things in our Universe – and this particular assemblage has a reputation for having an extremely large amount of starburst activity. It is also close enough for scientists to study. Its members were all discovered and cataloged by Sir William Herschel on this very night – 223 years ago! The northernmost, NGC 833, is known as H II.482, roughly of magnitude 13, followed by NGC 835 (H II.483) which holds a magnitude of 12. Next in line is NGC 838 (H II.484) at close to magnitude 13, followed by southernmost NGC 839 (H II.485) at magnitude 13. Not easy… But this beautiful crescent of four is worth the effort. If Herschel could do it – so can you!

Saturday, November 29, 2008 – Today in 1961 Enos the Chimp launched into fame! His story is a long and colorful one – but Enos was a true astronaut. Selected to make the first American orbital animal flight only three days before the launch, he flew into space on board Mercury-Atlas 5 and completed his first orbit in just under 90 minutes. Although Enos was scheduled to complete three orbits, he was brought back due to “attitude difficulties.” But whose? Malfunctions caused the chimp to be repeatedly shocked when performing the correct maneuvers, but Enos continued to perform flawlessly – and was said to run and jump enthusiastically on board the recovery ship, shaking the hands of the crew.

Although he died a year later from an unrelated disease which could not be cured at the time, Enos the chimp remains one of our most enduring space heroes. Tonight let’s monkey around with a planetary nebula as we’ll take a look at 8th magnitude NGC 246 about five degrees north of Beta Ceti.

On the large side as planetaries go, this variegated shell of gas envelops a dying star about 1600 light-years away. Once upon a time, the star was much like our Sun, but over thousands of years its atmosphere expanded, interacting with the gas and dust in the interstellar medium to create what you see tonight. With the outer shell visible to even small telescopes, larger aperture can spot the fainter member of the binary at the heart of this planetary…a star well on it’s way to becoming a white dwarf.

Discovered by Sir William Herschel, it is often referred to as the “Skull” nebula, but perhaps tonight you’ll see the smiling face of Enos forever leaving its mark on space!

Sunday, November 30, 2008 – Just as a curiosity, on this day in 1954, Elizabeth Hodges was struck by a five kilogram meteorite in Alabama. Duck! If you’re out at sunset tonight, you’ll be struck by the beauty of the slender crescent Moon illuminated by Earthshine. Not far away, look for the pairing of Venus and Jupiter, because things are going to get a lot cozier as the last month of the year begins!

Before the Moon once again interferes with study, last take one last look at Cetus before we move on. Our last target is a beauty – one which can be seen with larger binoculars, is easy with a small telescope, and becomes breathtaking with large aperture. Set your sights on bright Beta and drop less than three degrees south-southeast for NGC 247 (RA 00 47 09 Dec -20 45 38)…

As one of the largest members of a group of galaxies located around our galactic south pole, NGC 247 seems to be standing still in space – at a distance of six to eight million light-years. At its core is a near stellar-sized nucleus – a bright, central mass of stars which dominates its patchy looking structure. Look closely at its northern edge, for NGC 247 sports a huge area of dark, obscuring dust – or what may just be an empty space between its clouds of stars. Note a bright star caught on its southern flank.

While you may find this low surface brightness galaxy a bit difficult unless you stick with the most minimal of magnification, you can not only congratulate yourself for capturing another Herschel “400” object, but Bennett 3 as well.

Until next week? As for the Moon… But keep on reaching for the stars!

This week’s awesome photos are: Hickson 16 – Credit: Palomar Observatory, courtesy of Caltech, Enos (and handler) – Credit: NASA, NGC 246 (south is up) – Credit: Palomar Observatory, courtesy of Caltech and NGC 247 – Credit: Palomar Observatory, courtesy of Caltech. We thank you so much!

Posted on by Fraser Cain

Diameter of Neptune

Neptune compared to Earth. Image credit: NASA

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The diameter of Neptune is approximately 49,500 km. This makes Neptune the 4th largest planet in the Solar System, after Jupiter, Saturn and Uranus.

I say approximately because the diameter of Neptune changes depending on where you measure it. Neptune is rotating on its axis, completing a full day once every 16 hours or so. This rapid rotation flattens Neptune out slightly so that the diameter measured from pole to pole is less than the equatorial diameter.

Neptune’s polar diameter is 48,682 km. While its equatorial diameter is 49,528 km. In other words, points on the equator are 423 km more distant from the center of Neptune than the poles.

Want some comparison? The diameter of Neptune is about 3.9 times the diameter of Earth.

We have written many stories about Neptune for Universe Today. Here’s an article about how Neptune’s south pole is the warmest part of the planet.

If you’d like more information on Neptune, take a look at Hubblesite’s News Releases about Neptune, and here’s a link to NASA’s Solar System Exploration Guide to Neptune.

We have recorded an entire episode of Astronomy Cast just about Neptune. You can listen to it here, Episode 63: Neptune.

Posted on by Fraser Cain

How Long is a Day on Neptune?

Rotation of Neptune. Image credit: Hubble

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A day on Neptune is 16 hours, 6 minutes and 36 seconds.

Wait, not so fast! Here’s the problem. Neptune isn’t a single solid object like the terrestrial planets, so different parts of the planet rotate at different speeds. This is a process that astronomers call differential rotation. Neptune’s equatorial zone takes about 18 hours to complete a rotation – that’s slower than the planet’s averate 16.1 hour rotation period. And the polar regions can take just 12 hours to rotate; much more quickly than the average.

This big difference in rotational rate between the equatorial regions and the planet’s poles means that Neptune has a strong latitudinal wind shear. This helps to generate the strongest winds in the Solar System. Astronomers have clocked winds on Neptune going as fast as 2,400 km/hour (1,500 miles/hour).

We have done several stories about Neptune on Universe Today. Here’s an article about movies of Neptune captured by Hubble. These show its rotation.

If you’d like more information on Neptune, take a look at Hubblesite’s News Releases about Neptune, and here’s a link to NASA’s Solar System Exploration Guide to Neptune.

We have recorded an entire episode of Astronomy Cast just about Neptune. You can listen to it here, Episode 63: Neptune.

Posted on by Fraser Cain

What Color is Neptune?

Neptune, captured by Voyager 2. Image credit: NASA

The color of Neptune is a bright azure blue. During its flyby in 1989, NASA’s Voyager 2 revealed the bright blue color, different from the pale blue color of Uranus. So why does Neptune have this color?

The answer to Neptune’s color comes from its cloud tops. The upper atmosphere of Neptune is made up of 80% hydrogen, 19% helium with a trace 1% amount of methane and other ices, like ammonia and water. Methane absorbs light at 600 nm, which is the red end of the spectrum of visible light.

Like all the planets in the Solar System, the light we see coming from Neptune is actually reflected light from the Sun. These methane clouds absorb the red end of the spectrum, and allow the blue end of the spectrum to bounce back out. So when you see the color of Neptune, you’re seeing reflected sunlight with the red light stripped out.

From a distance, Neptune looks just like a blue ball, but as you get closer you can see variations in its clouds. Lighter clouds of methane hang above the lower cloud deck. Powerful storms whip across the surface of Neptune; the fastest storms in the Solar System are on Neptune, with winds exceeding 2,400 km/hour. Neptune has a large dark storm, similar to the Great Red Spot on Jupiter.

We have written many articles about Neptune on Universe Today. Here’s an article about “movies” of Neptune captured by Hubble. And some additional images captured by Hubble that really show the color of Neptune.

If you’d like more information on Neptune, take a look at Hubblesite’s News Releases about Neptune, and here’s a link to NASA’s Solar System Exploration Guide to Neptune.

We have recorded an entire episode of Astronomy Cast just about Neptune. You can listen to it here, Episode 63: Neptune.

Posted on by Fraser Cain

What is the Atmosphere of Neptune Like?

Neptune, captured by Voyager. Image credit: NASA/JPL

The atmosphere of Neptune is similar to all the large planets in the Solar System; it mostly consists of hydrogen and helium, with trace amounts of methane, water, ammonia and other ices. But unlike the other gas planets in the Solar System, Neptune’s atmosphere has a larger proportion of the ices. It’s the methane in the planet’s upper atmosphere that give it its bright blue color.

At the highest altitudes, where the Neptune’s atmosphere touches space, it consists of about 80% hydrogen and 19% helium. There’s also a trace amount of methane. The light we see from Neptune is actually the reflected light from the Sun. Although the entire spectrum of light hits Neptune. This trace amount of methane absorbs light from the red end of the spectrum, while allowing the blue light to bounce back out. The color of Neptune’s atmosphere is brighter than Uranus, which has a similar atmosphere; astronomers aren’t sure why there’s such a dramatic color difference.

The upper level clouds on Neptune occur at the point where pressures are low enough for methane to condense. Astronomers have photographed these high altitude clouds forming shadows onto the lower cloud deck below. Deeper down inside Neptune, temperatures should get up to 0 C, where clouds of water might form.

As with the other planets, the atmosphere of Neptune is broken up into distinct bands of storms. In fact, the fastest moving winds in the Solar System occur at Neptune – winds have been clocked at 2,400 km/h (1,500 miles per hour). Some storms can grow large and remain for long periods of time. Neptune has its own Great Dark Spot, similar to the Great Red Spot on Jupiter.

We have written many articles on Universe Today about the atmosphere of Neptune and its storms. Here’s an article about the weather in springtime on Neptune, and how Neptune’s south pole might be the warmest place on the planet.

If you’d like more information on Neptune, take a look at Hubblesite’s News Releases about Neptune, and here’s a link to NASA’s Solar System Exploration Guide to Neptune.

We have recorded an entire episode of Astronomy Cast just about Neptune. You can listen to it here, Episode 63: Neptune.

Posted on by Astronomy Cast

Podcast: Molecules in Space

Molecules in Space

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As part of her trip to England, Pamela had a chance to sit down with Oxford astrophysicist Chris Lintott and record an episode of Astronomy Cast. From the first stars to the newest planets, molecules and the chemistry that allows them to form affects all aspects of astronomy. While most astronomers group molecules into three bins of hydrogen, helium and everything else, there are a few who do proper chemistry by studying the sometimes complex molecules that form between the stars.

Click here to download the episode.

Or subscribe to: astronomycast.com/podcast.xml with your podcatching software.

Molecules in Space – Transcript and show notes.

Posted on by Nancy Atkinson

Chandrayaan-1 Feeling the Heat

Moon imagery from two different cameras on Chandrayaan-1. Credit: ISRO

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India’s Chandrayaan-1 spacecraft has successfully sent back some of its first science data and images from the moon, but the spacecraft is also experiencing rising temperatures, and mission managers have decided to use the instruments sparingly to avoid overheating. Chandrayaan-1 is currently orbiting over the sunlit side of the moon, and a rise in temperatures inside the spacecraft was expected, but still is a cause for concern. “This rise and fall in temperature inside a satellite is a normal cyclical process,” Mylswamy Annadurai, project director of Chandrayaan-I, told a newspaper in India, The Indian Express. “There is nothing unusual about it. But since this is the first cycle being faced by Chandrayaan, we are being extra cautious. We have decided to wait till the temperatures dip to bring the mission into the operational phase.” As of now, all but two of the instruments onboard have been switched on and tested. But only one instrument at a time is being used, and the two inactive instruments won’t be turned on until engineers know spacecraft is cool enough.

But scientists released a very nice video from the Terrain Mapping Camera…

Here’s a link to the movie of images stitched together for a view of flying over the Moon. The videos at ISRO only works in Internet Explorer. Find the science images at ISRO’s site here.

During the current orbital phase the spacecraft is almost continually in the sun and experiencing ‘summer.’ The Moon also radiates heat as it receives energy from the sun. The spacecraft’s temperature is expected to stabilize by the end of December. Until then, scientists will use one instrument at a time, but hope to operate all instruments simultaneously by mid-January.

Chandrayaan-1 has a heater, which is capable of increasing the temperature during the ‘winter’ but there is no cooling mechanism. If temperatures start reaching the upper limit, there would be no option but to switch off all the instruments.

Image from the TMC of the Moon's polar region. Credit: ISRO
Image from the TMC of the Moon's polar region. Credit: ISRO

The two instruments that haven’t been turned on yet are not only more sensitive to heat but also to high voltage. One is the Swedish sub-atomic reflecting analyzer (SARA), which will image the Moon’s permanently shadowed polar regions. The other is the Indian X-ray spectrometer, HEX, which will study radioactive emissions from the lunar surface.

“We thought it would be wise to wait for the temperature to go down before testing them,” Annadurai said. The extra-cautiousness on the part of mission scientists is only because this is Chandrayaan’s first experience with such phenomenon. “We are well within the upper limit of the spacecraft’s temperature bracket. But we want to remain in this comfort zone as it is our first experience,” Annadurai added.

Chandrayaan-1 carries 11 payloads, including a Terrain Mapping Camera (TMC), Hyper Spectral Imager (HySI), Lunar Laser Ranging Instrument (LLRI), High Energy X-ray Spectrometer (HEX), Moon Impact Probe (MIP), Chandrayaan-1 X-ray Spectrometer (C1XS), Smart Near-IR Spectrometer (SIR-2), Radiation Dose Monitor Experiment (RADOM), Sub Kev Atom reflecting Analyser (SARA), Miniature Synthetic Aperture Radar (MiniSAR) and Moon Mineralogy Mapper (M3).

Source: Indian Express, ISRO