Ganymede

Ganymede was discovered in 1610 by astronomer Galileo Galilei. It is named for the mythical Greek son of a King who was carried to the sky by Zeus posing as an eagle.

Moon Profile

Diameter: 5,268 km
Mass: 1.4819 × 10 ^23 kg
Orbits: Jupiter
Average Distance from Jupiter: 1,070,400 km
Length of Orbit: 7 days, 3 hours
Surface Temperature: 110 K (-163.5 C)

Facts About Ganymede

·         Ganymede is the largest moon in the solar system, and is larger than the planet Mercury. If it were not orbiting as Jupiter’s second-largest moon, it could be considered a dwarf planet.

·         Ganymede is the only moon in the solar system known to have a substantial magnetosphere. That implies there is something inside helping to generate a strong magnetic field.

·         Like Europa, Ganymede is thought to have a subsurface ocean, overlying a liquid iron and nickel core. That core is what helps generate the magnetic field.

·         The surface of Ganymede is icy and covered with two main types of landscape: young, lighter regions and darker, older and cratered terrain. The dark areas appear to contain clays and organic materials.

·         Ganymede was likely formed in place around the infant Jupiter in the early solar system. Several smaller worlds likely accreted together to make this moon.

·         Ganymede has a thin atmosphere that appears to contain oxygen. This was confirmed by Hubble Space Telescope observations. The oxygen is likely freed as water ice on the surface is broken apart into hydrogen and oxygen by solar radiation.

·         The first mission to explore Ganymede up close was Pioneer 10, followed by the Voyager missions, Galileo, and New Horizons.

·         Several missions to explore Ganymede in more detail have been suggested, but most have been cancelled or are still on the drawing boards.

Io

Io was discovered, along with Europa, Ganymede and Callisto by Galileo Galilei in 1610. It is the innermost of the four Galileans, and is a volcanic world.

Moon Profile

Diameter: 3,642 km
Mass: 8.9 x 10 ^22 kg
Orbits: Jupiter
Average Distance from Jupiter: 421,700 km
Length of Orbit: 1.8 days
Mean Surface Temperature: 110 K (-163.5 C)

Facts About Io

·         Io has more than 400 active volcanoes on its surface. They make this little moon the most actively volcanic world in the solar system.

·         The volcanism on Io is due to tidal heating, as the moon is stretched by Jupiter’s strong gravitational pull and by the lesser gravitational effects of the other satellites.

·         The volcanoes of Io are constantly erupting, creating plumes that rise above the surface and lakes that cover vast areas of the landscape.

·         Io has a very thin atmosphere that contains mostly sulfur dioxide (emitted from its volcanoes). Gases from the atmosphere escape to space at the rate of about a ton per second. Some of the material becomes part of a ring of charged particles around Jupiter called the Io plasma torus.

·         The volcanic plumes of Io rise up as high as 200 km, showering the terrain with sulfur, sulfur dioxide particles, and rocky ash.

·         Io has a number of mountains, some of which rise up as high as Mount Everest on Earth. The average height of Io’s peaks are around 6 km.

·         Io is made mostly of silicate rocks, and its surface is painted with sulfur particles from the volcanoes and frosts that are created as the atmospheric gases freeze out and fall to the ground.

·         Robotic missions to Io could study its volcanism in closer detail. No human missions are planned as yet, due to the extreme radiation environment and highly toxic atmosphere and surface.

Moon

The Moon (or Luna) is the Earth’s only natural satellite and was formed 4.6 billion years ago around some 30–50 million years after the formation of the solar system. The Moon is in synchronous rotation with Earth meaning the same side is always facing the Earth. The first unmanned mission to the Moon was in 1959 by the Soviet Lunar Program with the first manned landing being Apollo 11 in 1969.

Moon Profile

Circumference at Equator: 10,917.0 km
Diameter: 3,475 km
Mass: 73,476,730,924,573,500 million kg (0.0123 x Earth)
Orbits: The Earth
Average Distance from Earth: 384,400 km
Length of Orbit: 27.3 Earth days
Surface Temperature: -233 to 123 °C

Size Of The Moon Compared To The Earth

Phases Of The Moon (Northern Hemisphere)

Sun

The Sun or Sol, is the star at the centre of our solar system and is responsible for the Earth’s climate and weather. The Sun is an almost perfect sphere with a difference of just 10km in diameter between the poles and the equator. The average radius of the Sun is 695,508 km (109.2 x that of the Earth) of which 20–25% is the core.

Star Profile

Age: 4.6 Billion Years
Type: Yellow Dwarf (G2V)
Diameter: 1,392,684 km
Circumference at Equator: 4,370,005.6 km
Mass: 1,989,100,000,000,000,000,000 billion kg (333,060 x Earth)
Surface Temperature: 5500 °C

Size Of The Sun

Facts About The Sun

One million Earths could fit inside the Sun:
If a hollow Sun was filled up with spherical Earths then around 960,000 would fit inside. On the other hand if these Earths were squished inside with no wasted space then around 1,300,000 would fit inside. The Sun’s surface area is 11,990 times that of the Earth’s.

Eventually, the Sun will consume the Earth:
When all the Hydrogen has been burned, the Sun will continue for about 130 million more years, burning Helium, during which time it will expand to the point that it will engulf Mercury and Venus and the Earth. At this stage it will have become a red giant

The Sun will one day be about the size of Earth:
After its red giant phase, the Sun will collapse, retaining its enormous mass, but containing the approximate volume of our planet. When this happens, it will be called a white dwarf.

The Sun contains 99.86% of the mass in the Solar System:
The mass of the Sun is approximately 330,000 times greater than that of Earth. It is almost three quarters Hydrogen, whilst most of the remaining mass is Helium.

The Sun is an almost perfect sphere:
There is only a 10 kilometre difference in its polar diameter compared to its equatorial diameter. Considering the vast expanse of the Sun, this means it is the closest thing to a perfect sphere that has been observed in nature.

Light from the Sun takes eight minutes to reach Earth:
With a mean average distance of 150 million kilometres from Earth and with light travelling at 300,000 kilometres per second, dividing one by the other gives us an approximate time of 500 seconds, or eight minutes and 20 seconds. Although this energy reaches Earth in a few minutes, it will already have taken millions of years to travel from the Sun’s core to its surface.

The Sun travels at 220 kilometres per second:
The Sun is 24,000-26,000 light years from the galactic centre and it takes the Sun 225-250 million years to complete an orbit of the centre of the Milky Way.

The distance from the Sun to Earth changes throughout the year:
Because the Earth travels on an elliptical orbit around the Sun, the distance between the two bodies varies from 147 to 152 million kilometres. The distance between the Earth and the Sun is called an Astronomical Unit (AU).

The Sun is middle-aged:
At around 4.5 billion years old, the Sun has already burned off about half of its store of Hydrogen. It has enough left to continue to burn Hydrogen for approximately another 5 billion years. The Sun is currently a type of star known as a Yellow Dwarf

The Sun has a very strong magnetic field:
Solar flares occur when magnetic energy is released by the Sun during magnetic storms, which we see as sunspots. In sunspots, the magnetic lines are twisted and they spin, much like a tornado would on Earth.

The temperature inside the Sun can reach 15 million degrees Celsius:
At the Sun’s core, energy is generated by nuclear fusion, as Hydrogen converts to Helium. Because hot objects generally expand, the Sun would explode like a giant bomb if it weren’t for its enormous gravitational force.

The Sun generates solar wind:
This is a stream of charged particles, which travels through the Solar System at approximately 450 kilometres per second. Solar wind occurs where the magnetic field of the Sun extends into space instead of following its surface.

Solar Eclipse

What Is A Solar Eclipse?

A solar eclipse is a natural event that takes place on Earth when the Moon moves in its orbit between Earth and the Sun (this is also known as an occultation). It happens at New Moon, when the Sun and Moon are in conjunction with each other. If the Moon was only slightly closer to Earth, and orbited in the same plane and its orbit was circular, we would see eclipses each month. The lunar orbit is elliptical and tilted with respect to Earth’s orbit, so we can only see up to 5 eclipses per year. Depending on the geometry of the Sun, Moon and Earth, the Sun can be totally blocked, or it can be partially blocked.

During an eclipse, the Moon’s shadow (which is divided into two parts: the dark umbra and the lighter penumbra) moves across Earth’s surface. Safety note: do NOT ever look at the Sun directly during an eclipse unless it is during a total solar eclipse. The bright light of the Sun can damage your eyes very quickly.

Solar Eclipse Types

TOTAL SOLAR ECLIPSE

A total solar eclipse occurs when the Moon completely blocks the solar disk. In a total solar eclipse, the narrowest part of the path (where the Sun is completely blocked and the Moon casts its darkest shadow (called the umbra)) is called the “zone of totality”.

Observers in this path see a darkened Sun (often described as a “hole in the sky”) with the ghostly glow of the solar corona extending out to space. A phenomenon called “Bailey’s Beads” often appears as sunlight shines out through valleys on the lunar surface. If the Sun is active, observers can also see solar prominences, loops, and flares during totality. A total solar eclipse is the ONLY time when it is safe to look directly at the Sun. ALL other solar observations (even in partial phases) require special solar filters so that you do not harm your eyes.

Total solar eclipses have not always been visible from Earth. In the past, the Moon was too close to Earth and during eclipses it completely blotted out the Sun’s disk. Over time, the lunar orbit has changed at the rate of just over 2 cm per year and in the current epoch, the alignment is nearly perfect at times. However, the Moon’s orbit will continue to widen, and in perhaps 600 million years, total solar eclipses will no longer occur. Instead, future observers will see partial and annular eclipses only.

ANNULAR SOLAR ECLIPSE

Not every solar eclipse is a total one. When the Moon is farther away in its orbit than usual, it appears too small to completely cover the Sun’s disk. During such an event, a bright ring of sunlight shines around the Moon. This type of eclipse is a called an “annular” eclipse. It comes from the Latin word “annulus” which means “ring”.

The period of annularity during such an eclipse can last anywhere from 5 or 6 minutes to up to 12 minutes. However, even though the Sun is mostly covered by the Moon, enough bright sunlight escapes during annularity that observers cannot ever look at the Sun directly. These events require eye protection throughout the entire eclipse.

PARTIAL SOLAR ECLIPSE

A partial solar eclipse occurs when Earth moves through the lunar penumbra (the lighter part of the Moon’s shadow) as the Moon moves between Earth and the Sun. The Moon does not block the entire solar disk, as seen from Earth. Depending on your location during a partial eclipse, you might see anything from a small sliver of the Sun being blotted out to a nearly total eclipse.

To view any eclipse safely, use approved filters or use an indirect method of viewing, such as projecting sunlight through a telescope and onto a white piece of paper or cardboard. NEVER look at the Sun through a telescope unless it has the appropriate filter. Blindness and severe eye damage can result due to improper observation technique.

Comet

What Is A Comet?

A comet is a very small solar system body made mostly of ices mixed with smaller amounts of dust and rock. Most comets are no larger than a few kilometres across. The main body of the comet is called the nucleus, and it can contain water, methane, nitrogen and other ices.

When a comet is heated by the Sun, its ices begin to sublimate (similar to the way dry ice “fizzes” when you leave it in sunlight). The mixture of ice crystals and dust blows away from the comet nucleus in the solar wind, creating a pair of tails. The dust tail is what we normally see when we view comets from Earth.

A plasma tail also forms when molecules of gas are “excited” by interaction with the solar wind. The plasma tail is not normally seen with the naked eye, but can be imaged. Comets normally orbit the Sun, and have their origins in the Oort Cloud and Kuiper Belt regions of the outer solar system.

Facts About Comets

There are many misconceptions about comets, which are simply pieces of solar system ices travelling in orbit around the Sun. Here are some fascinating and true facts about comets.

1.    The nucleus of a comet is made of ice and can be as small as a few meters across to giant boulders a few kilometres across.

2.    The closest point in a comet’s orbit to the Sun is called “perihelion”. The most distant point is called “aphelion”.

3.    As a comet gets closer to the Sun, it begins to experience heat. That causes some of its ices to sublimate (similar to dry ice sizzling in sunlight). If the ice is close to the comet’s surface, it may form a small “jet” of material spewing out from the comet like a mini-geyser.

4.    Material streams from comets and populates the comet’s orbit. If Earth (or another planet) happens to move through that stream, those particles fall to Earth as meteor showers.

5.    As a comet gets close to the Sun, it loses some of its mass due to the sublimation. If a comet goes around enough times, it will eventually break up. Comets also break up if they come TOO close to the Sun or another planet in their orbits.

6.    Comets are usually made of frozen water and supercold methane, ammonia and carbon dioxide ices. Those are mixed with rock, dust, and other metallic bits of solar system debris.

7.    Comets have two tails: a dust tail (which you can see with the naked eye) and a plasma tail, which is easily photographed but difficult to see with your eyes.

8.    Comet orbits are usually elliptical.

9.    Many comets formed in the Oort Cloud and Kuiper Belts, two of the outermost regions of the solar system.

10. Comets are not spaceships or alien bases. They are fascinating bits of solar system material that date back to the formation of the Sun and planets.

Andromeda galaxy

The Andromeda Galaxy (M31) is the closest large galaxy to the Milky Way and is one of a few galaxies that can be seen unaided from the Earth. In approximately 4.5 billion years the Andromeda Galaxy and the Milky Way are expected to collide and the result will be a giant elliptical galaxy. Andromeda is accompanied by 14 dwarf galaxies, including M32, M110, and possibly M33 (The Triangulum Galaxy).

Galaxy Profile

Designation: M31, NGC 224
Type: Spiral
Distance from Milky Way: 2.5 million light-years
Diameter: 260,000 light-years
Mass: 400 billion solar masses
Number of Stars: 1 trillion

Facts About Andromeda

·         While Andromeda is the largest galaxy in the Local Cluster it may not be the most massive. The Milky May is thought to contain more dark matter, which could make it much more massive.

·         Since it is the nearest spiral galaxy to us, astronomers use the Andromeda Galaxy to understand the origin and evolution of such galaxies.

·         The Andromeda Galaxy is approaching the Milky Way at approximately 100 to 140 kilometres per second.

·         The Andromeda Galaxy has a very crowded double nucleus. Not only does it have a massive star cluster right at its heart, but it also has at least one supermassive black hole hidden at the core.

·         The spiral arms of the Andromeda Galaxy are being distorted by gravitational interactions with two companion galaxies, M32 and M110.

·         The Andromeda Galaxy has at least two spiral arms, plus a ring of dust that may have come from the smaller galaxy M32. Astronomers think that it may have interacted more closely with Andromeda several hundred million years ago, when M32 plunged through the heart of its larger neighbor.

·         There are at least 450 globular clusters orbiting in and around the Andromeda Galaxy. Some of them are among the most densely populated globulars ever seen.

·         The Andromeda Galaxy is the most distant object you can spot with the naked eye.

You need a good spot away from bright lights in order to see it.