Spacewatch: CME, Mercury and Venus?

    Stephen Marsh Stephen Marsh | 15:30 PM, Wednesday, 5 October 2011

    Distance travelled ~ 714'327'200 km

    While we have been enjoying the wonderful sunshine down on Earth (especially the recent record october warmth in the UK) - space has also been throwing up some pretty stunning weather. Yesterday, October 4th, a massive solar flare exploded from the surface on the far side of the Sun. It blasted a spectacular coronal mass ejection or CME into space. A CME is a massive burst of solar wind and plasma containing electrons and protons that blast out from the Sun's surface. They are associated with solar flares and tend to develop in areas of high solar activity such as Sun spots.

    The October 4th CME was recorded by the Solar and Heliospheric Observatory

    Scientists from the Goddard Space Weather Lab have plotted the course of the CME and discovered it is heading directly for the planet closest to the Sun, Mercury. The cloud of highly energised plasma and particles won't affect the planet but could disrupt the MESSENGER probe in orbit around Mercury.

    cme forecast track

    To watch the moving image click here

    It is possible that the CME may then hit Venus on Oct. 6th, but it is not predicted to hit Earth.

    What happens when CME's hit Earth?
    When CMEs do come our way the shockwave from the highly energized particles can cause a geomagnetic storm that can disrupt our magnetic shield. This can trigger dynamic auroras or Northern Lights [aurora borealis] in the northern hemisphere or Southern Lights [aurora australis] in the southern hemisphere. CMEs hitting earth can also cause disruption to radio transmissions, damage satellites and cause power cuts by knocking out electrical power cables.

    They don't present a health risk for us on the surface because of our protective magnetic shield and atmosphere. But they can present problems for astronauts and even people in high altitude planes due to increased risk of exposure to radiation. But it is thought that any long-term health risk are unlikely.

    Spacewatch - great red spot on jupiter leaves hurricane irene in the shade

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    Mark Thompson Astronomy Mark Thompson Astronomy | 16:30 PM, Wednesday, 24 August 2011

    Distance travelled ~ 606'376'800

    As Hurricane Irene gathers strength it reminds me of the hurricane that has been raging on Jupiter for at least the last 350 years. Called rather imaginatively, the Great Red Spot (GRS) it was first observed in the 17th Century by Giovanni Cassini through the recently invented called the telescope. Its not just its longevity that brings it whirling into the record books though, its size is also impressive, measuring three times as big as the Earth, compare that to Irene which is about 400km in diameter and you realise quite how big a storm it is.

    jupiter's great red spot

    As Voyager 1 flew by Jupiter in 1979, it captured this photo of the Great Red Spot. Credit/Nasa

    Jupiter, unlike Earth, is a planet made up almost entirely of gas with a fluid core but when we look at it through telescopes, its the tops of the dense atmosphere that we can see. Heating from the Sun and from internal sources, drives the convective activity in the atmosphere to produce the familiar high and low weather systems. Just like the Earth, its these high's and low's which effectively cause air to move and produce wind. Its here though that the similarities end. Simple observation from even modest telescopes will reveal strange belt structures in the atmosphere that seem symmetrical in both northern and southern hemispheres.

    jupiter

    NASA/Freddy Willems, Amateur Astronomer, July 26 2011

    In one of these belts, called the Southern Equatorial Belt, we can readily see the GRS which is an anticyclonic storm (a storm which rotates anti-clockwise) taking about 6 days to complete one revolution. Its elliptical shape seems to be due to the fast jet streams that neighbour it, blowing easterly on the south and westerly to the north. Infrared observations have shown that the temperature of the GRS is lower than that of the surrounding clouds suggesting a higher altitude, estimated to be towering over neighbouring jet streams by 8km. From such a monstrous storm you might expect astronomical wind speeds but surprisingly modest speeds of 430km per hour are measured, compared to Irene's more sedate maximum speeds of 160km per hour.

    The colour of the spot isn't even stable, changing from pale pink to a deep red but what causes this colour remains a mystery. We do know that its affected by environmental factors though as the darker central region always appears slightly warmer than the paler, cooler surroundings. Its perhaps the presence of complex organic compounds such as red phosphorous that gives it its distinctive colour but for now, the GRS remains one of the beautiful yet enigmatic mysteries of the Solar System.

    Aphelion: shouldn't earth be at its coldest today?

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    Stephen Marsh Stephen Marsh | 15:30 PM, Monday, 4 July 2011

    Distance travelled ~ 475'968'000 km: day 185

    Today July 4 is a rather special day in our annual journey around the Sun. At 15.00 GMT Earth will be at the furthest point away from the Sun it will reach all year. I know it sounds bizarre considering how warm it is today but it's true, and it's all down to our orbit.

    The Earth's orbit around the Sun is not a perfect circle. It's an ellipse and the Sun does not sit at the centre, it's offset to one side. So today we are 5 million kilometres further away from the Sun than when we were closest to the Sun six months ago in January during Perihelion. And if you remember it was pretty cold in January so you might ask why isn't our proximity to the Sun in winter warming us and our increased distance away from the Sun in summer cooling us down?

    sun at aphelion and perihelion

    Image © 2001-2011, Anthony Ayiomamitis

    The truth is our elliptical orbit and our distance from the Sun is not the primary driving force behind our climate. So what is?

    Well number one is the that fact that the Earth is tilted at 23.4 degrees from vertical. During Perihelion the northern hemisphere is tilted away from the Sun, so received less solar radiation and we get winter. In our summer we are tilted towards the Sun so despite being farther away on our orbit we get increased solar radiation. Which is why today in July it's lovely and warm.

    But what about the southern hemisphere? Well it's a bit more complex down there. Earth is closest to the Sun during their summer when they are tilted towards the Sun and this means they get 7% more solar radiation. Therefore you'd expect the southern hemisphere summer to be a lot warmer than the northern summer. But it's not, in fact it's actually colder.

    And now at Aphelion it's winter down south, and the hemisphere is both furthest away and tilted away from the Sun. So you'd think it's winter would be a lot colder, what with the tilt pushing the hemisphere away from the Sun. Well in fact it's warmer than our winters. And that's all because of the ratio of land to oceans in the hemispheres. The northern hemisphere has a lot of land but the southern hemisphere is predominantly water with very little land and it's this that is powering the climate.

    While land reacts very fast to solar heating, it warms up and cools down very quickly. The oceans react very slowly to solar energy. They take a long time to warm up and a long time to cool down. This means that at perihelion in their summer the oceans haven't absorbed enough energy to warm up the atmosphere, they are still cool from the previous winter, so they keep the temperatures cool. In the southern hemisphere winter it's the opposite. The oceans have held onto some of the heat they absorbed during the summer and are keeping the air above warm.

    So even though our elliptical orbit takes us at this point of the year further away from the Sun than it will for the rest of the year, it's warm in the north because we are tilting towards the Sun and a milder winter in the south because of the actions of the oceans.

    It's Summer Solstice and we head to Aswan Egypt, just like Eratosthanes

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    Stephen Marsh Stephen Marsh | 10:30 AM, Tuesday, 21 June 2011

    Distance travelled ~ 442'521'600 km: day 172

    Today Kate Humble and some of the 23 Degrees team are in Aswan, Egypt. They are there to reveal something fascinating about the Summer Solstice and the tilt of our planet.

    The Earth's tilt reveals itself every time we step out in the Sun but none more so than today on the solstice. The angle between the Sun and the Earth was first worked out over 2000 years ago. It was a discovery made near the city of Aswan, at the bottom of an ancient well by a Greek scientist and philosopher, Eratosthanes.

    Eratosthanes was a poet, an athlete and a true polymath. He invented the word geography and even created a map of the world. He tried to write a chronology of world history and he invented the leap day. He also proposed a simple algorithm to work out prime numbers and all the time he was the head librarian of the library at Alexandria, the greatest treasure trove of knowledge of its time.

    The story goes that 250 BCE on the summer solstice Eratosthanes was in Aswan and at midday, he looked down to the bottom of a well and saw his reflection staring back at him. Now as with most geniuses he noticed something that the rest of us would have missed. Something that told him about the very nature of our relationship with the sun.

    When Eratosthanes looked at his reflection in the water in the well, he noticed he threw no shadow because the Sun was directly overhead. Now to most people that wouldn't have meant much but for Eratosthames it was an important revelation. Let me explain. Eratosthames didn't live here in Aswan, he lived 500 miles north in Alexandra. You might ask why that's significant. Well history has it that he noticed that when he was in Alexandria at the same time, on the Summer solstice on a previous year he did cast a small shadow. In fact he'd measured its length and angle.

    So when he saw there was no shadow in Aswan he realised that at the very same moment, midday on the solstice, the Sun's position in the sky was different in Alexandra to Aswan. So, by calculating the angle of the shadow he cast in Alexandria, and its distance to the well here, Eratosthenes was able to estimate the circumference of the earth with an astonishing 98% accuracy. And using the same data, he was able to establish the tilt of the Earth's axis, obtaining a value of 23° 51' 15". A pretty amazing result without GPS and modern computing methods.

    From watching the position of the Sun, Eratosthanes observed something else. After June 21, shadows appear here once again at noon, and over the coming days, they lengthen. So this day and this place marks the most northerly apparent position of the Sun due to that 23 ½ degree tilt. But tracing a line of latitude, west to east, across the planet one can see the same thing. Aswan sits just above a hypothetical line of latitude, a line we know as the Tropic of Cancer. A line that circles the world at 23.4 degrees above the equator.

    The northward drift of the Sun in our sky that begun at the Spring Equinox on March 21 ends now on the Summer Solstice. From this day on, in the northern hemisphere, the hours of daylight will start to reduce and the Sun will track a lower arc in the sky.

    Kate and the team are visiting a well reputed to be the very same well that Eratosthanes looked down all those years ago, to tell the story of this remarkable man and his discovery about the tilt of our planet.

    Sun-Earth-Moon relationship: First total lunar eclipse of 2011

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    Aira Idris Aira Idris | 13:15 PM, Tuesday, 14 June 2011

    Distance travelled ~ 424'512'000 km: day 165

    One of the few significant things Earth and the Moon share is their relationship with the Sun. To an observer on Earth at least - as different portions of both the Earth and Moon's surfaces are illuminated, this signifies the movement of time and the root of our calendar, which is very important.

    On 15th/16th June we will observe a unique point in the Sun-Earth-Moon annual relationship - a total lunar eclipse and the first for this year.

    total lunar eclipse 2000

    Image courtesy of Fred Espenak/NASA

    It takes the Moon 27 1/3 days to orbit the Earth (lunar month 29 ½ days), going through the new Moon, first quarter, full Moon, last quarter and back to new Moon. A total lunar eclipse happens when there's a full Moon and the Moon passes through a part of the Earth's shadow, known as the umbra - an area not directly receiving the Sun's rays.

    Although there is a full Moon every month, we don't get a total lunar eclipse each month because the Moon's orbit is not in the same plane as the Earth's around the Sun (the ecliptic). From the image below we can see that the Moon's orbit goes over and under the Earth's orbital plane around the Sun.

    geometry of a lunar eclipse

    Image courtesy Wikimedia commons

    The inclination of the Moon's orbit is around 5 degrees to the Earth's orbit, and passes through the ecliptic only twice a month at a pair of points called the ascending and descending nodes. This is where the Nodal Axis is aligned with, or pointing at, the Sun.

    The period when the Earth completely blocks the Sun's rays from the Moon is when we experience a total lunar eclipse - known as totality. This moment repeats itself every 6 months.

    For this week's eclipse the best placed observers to see it in it's entirety are those in East Africa, central Asia, Middle East and West Australia, lasting a total of 1 hour and 6 minutes. For Europe and South America we will miss the beginning of the show and places like west Australia will miss the end - check specific times for your location. North America completely misses the total lunar eclipse.

    Penumbral Eclipse Begins: 17:24:34 UT
    Partial Eclipse Begins: 18:22:56 UT
    Total Eclipse Begins: 19:22:30 UT
    Greatest Eclipse: 20:12:37 UT
    Total Eclipse Ends: 21:02:42 UT
    Partial Eclipse Ends: 22:02:15 UT
    Penumbral Eclipse Ends: 23:00:45 UT

    (credit NASA)

    What can you expect to see? The shade of the Moon at eclipse is hard to predict because of the Earth's atmosphere. Although the Earth will block out the Sun during totality, the Sun's rays will still penetrate through the Earth, and mixed with the dust and cloud in the atmosphere the total lunar eclipse may take a variation of different shades. Volcanic ash can also affect the shade of the total lunar eclipse - turning it a darker shade of red. Ash from the recent eruption of the Puyehue volcano in Chile may have placed some sulphur dioxide into the stratosphere, according to atmospheric scientist Richard Keen of the University of Colorado.

    If you plan on observing or photographing the total lunar eclipse of June 15th/16th and would like to share your comments and images with the 23 Degrees team for a possible story or image gallery do get in touch.

    The next long lunar eclipse will be in 2018.

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