## The darker mornings

As I complete this post from my home in Manchester, England, it is 4:30 pm and already fairly dark outside. Many people think that it will continue to get dark earlier each day in the afternoon until we reach 21 December, the winter solstice. This, however, is not the case. The evenings in fact start to draw out a week or so before December 21, so it is already getting lighter in the evenings, although it does not start to get lighter in the mornings until early in the new year.

This post aims to explain this interesting phenomenon. (Those of you who have been following my blog for while and have a good memory may recall that I posted on this topic a couple of years ago 🙂 )

Sunrise and sunset in December

The table below shows the sunrise and sunset times for London for December at three day intervals.

In the table above, the daylight column shows the number of hours, minutes and seconds between sunrise and sunset. This clearly shows that 21 December has the shortest period of daylight, but while the time of sunrise continues to get later and later throughout the whole of December, the time of sunset stops getting earlier around 12 December.

The final column shows the solar noon, the time of day that the Sun is at its highest in the sky or, to put it another way, the mid-point between sunrise and sunset. The table shows that during December the solar noon drifts later by about 30 seconds each day.

Why does the solar noon shift ?

A solar day is the period of time between solar noon on one day and solar noon on the next day. The length of a solar day varies throughout the year. It is at its shortest, around 23 hours 59 minutes 38 seconds, in mid September and at its longest, around 24 hours 30 seconds around Christmas Day.

.

The graph shows the difference between the length of a solar day and its average value of 24 hours throughout the year.  For example, a value of 10 means a solar day is 24 hours 10 seconds long , 20 means a solar day is 24 hours 20 seconds long, and -10 means  a solar day is only 23 hours 59 minutes 50 seconds long.

As you can imagine, it would be complete chaos if our clocks and watches had to cope with days of different lengths, so we use 24 hours, the average over the whole year, for all timekeeping purposes.

So, in December solar days are on average 24 hours and 30 seconds in length, while our clocks and watches are still assuming that each day is exactly 24 hours.  This causes the day to shift about 30 seconds later each day,  as shown in the diagram below.  This explains why the evenings start drawing out before the shortest day, but it continues to get darker in the mornings until the new year.

Sunrise and sunset for London in December.

Why does the length of a solar day vary ?

The reason why the length of the solar day varies is due to two different factors.

1. The fact that the Earth moves in an elliptical orbit around the Sun and its speed varies, being faster in earlier January, when it is closer to the Sun and slower in early July, when it is further away.
2. The fact that the axis of the Earth’s rotation is tilted.

If you want to know more about how these  factors work together to vary the length of the solar day, see my post September 18 the Shortest Day.

What about the southern hemisphere ?

In the southern hemisphere 21 December is the summer solstice, the day with the most daylight. What happens is that the Sun starts rising later before December 21, but it doesn’t start getting dark earlier in the evening until well after December 21. This is illustrated in the table below, which shows the sunrise and sunset times for December for Wellington in New Zealand, which lies at a latitude of roughly 41 degrees South.

Final note

It is not strictly true to say that a solar day is on average exactly 24 hours long.  As readers of a previous post,  “The Days are Getting Longer’, will be aware the Moon is gradually getting further away from the Earth. In fact, equipment left on the Moon by the Apollo astronauts has confirmed that the average distance from the Earth to the Moon is increasing by about 4 cm a year.

-Image from NASA

As the Moon gradually saps energy from the Earth, the Earth’s rotation slows down, causing the length of a day to get gradually longer. In the year 1900 a mean solar day was 24 hours long. Now, in the early 21st century, a mean solar day is actually 24 hours 0.002 seconds long. To prevent the time we measure using accurate clocks from drifting away from the solar time we need to add an second called a leap second roughly every 18 months.

## July 8 2011- The Final Mission

On 8 July 2011 Atlantis took off for the final 13 day mission of the Space Shuttle programme and it remains to this day the last American spacecraft to carry humans into orbit.

The landing of Atlantis on 21 July 2011, which brought the Space Shuttle programme to a close – Image from NASA.

Development of the Space Shuttle

Prior to the Space Shuttle, all astronauts were launched into space in a small capsule which was stacked on top of a tower of one or more large rockets. It took months to build each launcher and space capsule, which could only be used for a single mission. This way of getting into space was very expensive and access to space had been restricted to a very small number of people. In today’s money each launch would cost hundreds of millions of dollars.

In the early 1970s, as the Apollo programme to put a man on the Moon was drawing to a close, the next stage of manned space exploration was logically seen as widening it out so that many more people would be able to go into space at a much lower cost. At the time many people thought that, with continual improvements in technology, travelling into space would become commonplace by the 2020s –  just like flying in a plane.

The Space Shuttle was announced by president Richard Nixon in 1972 as the first step in this process, saying it would be “…designed to to help transform the space frontier of the 1970s into familiar territory easily accessible to human endeavor in the 1980s and 1990s … It will revolutionize the transportation into space by routinizing it.” (Gehrman et al 2003:22)

Image from Wikimedia Commons

It was planned that there would  initially be a fleet of four Space Shuttles. Each would be launched like a traditional rocket into Earth orbit and after it had completed its mission would land like a conventional airplane on a runway. After it had landed, the shuttle would be refueled and serviced and could be launched again within 10 days. In 1972, when Nixon announced the approval of the Shuttle programme, NASA expected that they would be launching 50 shuttle missions a year by the time the shuttle was fully operational.  They estimated that it would cost \$5.15 billion (equivalent to \$30 billion in 2016 dollars) to design, develop and build the Shuttle fleet and each launch would cost \$7.7 million (\$45  million in 2016 dollars). At that time it was expected that the Shuttle would have a lifetime of 10-15 years and in the early 1990s the shuttle would be replaced by a new generation of more advanced spacecraft.

However, the development of the Space Shuttle was more complex and took much longer than expected.  By 1979 the programme was already three years late, with the date of the first planned launch having slipped from 1978 to 1981, and it was the equivalent of \$5 billion (in 2016 dollars) over budget.  President Jimmy Carter wanted to ensure that the programme was still worth continuing with and subjected it to an intensive review. The decision was taken to continue – a key factor being that it was needed to launch military surveillance satellites.

Space Shuttle missions

The Space Shuttle was first launched into Earth orbit in April 1981 and was the first, and so far the only, manned spacecraft which could take off like a rocket from a launch pad, go into orbit and then glide back to Earth to land like a plane on a runway. A total of 5 shuttles were built and between them they flew a total of 135 times between 1981 and 2011.  Sadly it never achieved anywhere near the frequency of flights originally planned. Over its 30 year lifetime there were, on average, only 4.5 Shuttle flights per year.

The first launch of the space shuttle on April 12 1981- Image from NASA

The much lower number of flights per year was for a number of reasons. One was that the minimum time interval between a Shuttle landing and it being ready for its next launch was much longer than the ten days originally planned. The three main engines needed to be removed from the Shuttle and carefully inspected before each flight for signs of any damage. Each Shuttle was covered by 30,000 protective insulating tiles to protect the spacecraft from damage due to the high temperatures when it re-entered the Earth’s atmosphere. Each of these tiles needed to be individually checked for damage and replaced if necessary. This was a time consuming task. Each tile was was designed to fit a particular place on the Shuttle and so was a slightly different shape from the others.

But the biggest reason for the lower frequency of flights were perhaps the two fatal accidents in 1986 and 2003, both of which stopped all Shuttle flights for a period of time.

In the first of these, on 28 January 1986, the Space Shuttle Challenger broke apart 73 seconds after take off, killing all the crew.

Space Shuttle Challenger – 15 seconds before its destruction – Image from NASA

Space Shuttle flights were suspended for nearly three years, while a commission under the chairmanship of former Secretary of State Williams Rogers investigated the cause of the accident and NASA put into place its recommendations.

After the accident one of the observations was that because NASA wanted to have as many Shuttle flights as possible, they had cut corners when it came to checking that a Shuttle was safe to launch. When Shuttle flights resumed in late 1988 there were fewer launches per year with a larger gap between them, to allow for additional safety checks. Before the accident, the Shuttle was intended to be the main vehicle to get NASA’s spacecraft into orbit, but after the accident NASA moved away from relying mainly on the Shuttle and went back to traditional non-reusable launchers as an alternative, which turned out to be a cheaper way of getting satellites into orbit. Prior to the accident, the Shuttle generated revenue, because private companies could pay NASA to launch their satellites on the Shuttle – indeed many of the early Shuttle flights carried such satellites. However, in August 1986, President Reagan made an announcement that the Shuttle would no longer carry any commercial satellites in order to focus on scientific and military objectives only. Although this might sound like good news for science, the problem was that the Shuttle was no longer generating any money, which in turn weakened the economic case for ongoing investment in it.

The second accident occurred on 1 February 2003 when the Space Shuttle Columbia broke apart during its re-entry into the Earth’s atmosphere.  The Columbia Accident Investigation Board (CAIB) was set up to investigate the cause of the accident and found it to be the result of damage to a wing of the Shuttle caused by foam debris hitting it at very high speed shortly after launch.  The CAIB found that there had been many similar “foam strikes” which had caused damage to the Shuttle over the years. However, because there had never been a serious accident NASA had become complacent and ignored the warnings which had previously been given by scientists from within the organisation.

The Space Shuttle Columbia crew tragically killed in February 2003 – Image from NASA

After the second accident, Space Shuttle flights were suspended for two and half years. When they did resume, only 20 more shuttle flights took place and all but one of these missions used the Shuttle to carry components to the International Space Station (ISS) which was being constructed in space and which NASA were committed to finishing. Flying to the ISS had the advantage that if the Shuttle were damaged on take off and couldn’t safely return to Earth then the crew could stay on the ISS until they could return to Earth on another spacecraft.

A remarkable machine

The Space Shuttle was one of the most complex machines ever built. Each Shuttle was assembled from over 2.5 million parts and had 370 km of wire in its electrical circuits. Weighing 4.5 millions pounds (2,000 tonnes) at launch, it could take a crew of seven astronauts up to an orbital velocity of 28,500 km/h, which is 25 times the speed of sound, in just over 8 minutes. The Shuttle could carry into orbit a payload the size of a small bus and weighing up to 26 tonnes (Gehrman et al 2003:14).

Although it never achieved its original objective of frequent flights into space, over its 30 year lifetime the shuttle launched numerous satellites, interplanetary probes (including the Galileo mission to Jupiter and its moons), and the Hubble Space Telescope.

The Hubble Space Telescope – launched by the Shuttle in 1990 – Image from NASA

Shuttle astronauts also conducted numerous science experiments in orbit, such as studying the affects of zero gravity on plant and animal life. It would not have been possible to construct the ISS without the shuttle, as it played a key role in ferrying components, supplies and crew there.

Costs of the programme.

One of the key failures of the programme is that both the development of the Shuttle and each Shuttle mission cost far more than the original estimates. According to NASA (2012), the total cost of the Space Shuttle from 1972 until the end of the programme in 2011 was \$113.7 billion. However, this figure is misleading because it is not adjusted for inflation. If we do this, the cost (in 2016 dollars) is around \$220 billion. This compares with a cost of \$175 billion in today’s money of the Apollo programme to put a man on the Moon (NASA 2014).

It we divide \$220 billion by the number of missions (135), The average cost of each Shuttle missiion works out at \$1.6 billion.  This is a very high figure and it would perhaps be fairer to ignore the upfront design and build costs and use the figure of how much it cost to launch a single Shuttle mission.  In NASA (2011) the figure given is around \$500 million in today’s money. This compares with a figure of only \$60 million to launch a Russian Soyuz spacecraft (Wade 2016)

The final mission

The final mission had a crew of four and the purpose of the mission was to deliver supplies and equipment to the ISS. The astronauts spent seven days aboard the ISS, joining the six astronauts who were already there.

The four members of the shuttle crew having a meal with the six astronauts already aboard the space station – Image from NASA

Inside the ISS the Space Shuttle crew presented the ISS crew with a US flag, which was then mounted on the hatch leading to Atlantis.  This particular flag is special because it was flown on the first Shuttle mission. It will remain on board the ISS until the next crew launched from the US retrieve it and bring it back to Earth.  It is still unclear when this will be.

Image from NASA

The future

Since the end of the Shuttle programme the only way astronauts can get to and from the ISS is by the Russian Soyuz spacecraft, a point worth remembering now that relations between the US and Russia are rather cool.  Soyuz was first flown in 1967 and its design has changed little since then. Like Apollo, it is a single use spacecraft. The astronauts return to Earth in a small capsule which has a heat shield to protect it during the most dangerous part of the mission re-entry. Currently NASA pay \$70 million per seat for each astronaut who flies in the Soyuz spacecraft (Wall 2013), which enables the Russian space agency to make a significant profit.

In the next few years US  spacecraft should return to space.  Rather than build a new craft to fly crew to and from the ISS, NASA administer a US-government funded programme called Commercial Crew Development (CCDev). After a lengthy evaluation process NASA announced on 16 September 2014 that Boeing and SpaceX had received contracts to provide crewed launch services to the ISS. At the moment there is no confirmed date when these companies will send their spacecraft to the ISS. Although both companies have ambitious pans to send crewed spacecraft in 2017, significant development and testing is still needed, so I expect it won’t be until 2018 at the earliest when the US crew will retrieve the flag.

In the medium term NASA are developing a spacecraft which will be able to take a crew to beyond low Earth orbit. However, this is not expected to carry crew until 2023. I will write about this spacecraft, which is called Orion, in a future post.

I hope you have enjoyed this post. While researching it I found the information in the Columbia Accident Investigation Board report a useful source. It gives a lot more background to the Space Shuttle programme than I could mention here. If you want to view the report I have created a references page on my blog where the it can be viewed or downloaded. To do this click here.

References

Gehrman, H.W., Barry,J. L., Deal, D. W., Hallock, J. N., Hess, K. W., Hubbard, G.S, Logsdon, J. M., Osberon, Ride, S. K., Tetrault, R. E., Turcotte, S. A., Wallace, S.B, Widnall, S. E. (2003) Columbia Accident Investigation Board -Report Volume I, Available at: www.thesciencegeek.org(Accessed: 15 July 2016).

NASA (2011) How much does it cost to launch a Space Shuttle?, Available at:http://www.nasa.gov/centers/kennedy/about/information/shuttle_faq.html#1 (Accessed: 9 July 2016).

NASA (2012) Space Shuttle era facts, Available at:https://www.nasa.gov/pdf/566250main_SHUTTLE%20ERA%20FACTS_040412.pdf(Accessed: 9 July 2016).

NASA (2014) Project Apollo: A Retrospective Analysis, Available at:http://history.nasa.gov/Apollomon/Apollo.html (Accessed: 15 July 2016).

Wade, M. (2016) Cost, Price, and the Whole Darn Thing, Available at:http://www.astronautix.com/c/costpriceanholedarnthing.html (Accessed: 10 July 2016).

Wall, M (2013) NASA to pay \$70 Million a seat to fly astronauts on Russian spacecraft,Available at: http://www.space.com/20897-nasa-russia-astronaut-launches-2017.html(Accessed: 10 July 2016).

## The evenings are drawing out already

As I complete this post, it’s completely dark outside and it’s only 5 o’clock in the afternoon. Today is 14 December, and most people I come across think that it will continue to get dark earlier and earlier in the afternoons until 21 December, the shortest day of the year (at least for those of us in the northern hemisphere). This, however, is not the case.  The evenings in fact start to draw out a week or so before December 21, so it is already getting lighter in the evenings, although it does not start to get lighter in the  mornings until  early in the new year.

This post aims to explain this interesting phenomenon. (Those of you who have been following my blog for while and have long memories may recall that I posted most of this material in a post called “The Shortest Day” in December last year 🙂 )

Sunrise and Sunset in December

The table below shows the sunrise and sunset times for London in December 2014.

In the table the daylight interval column shows the number of hours, minutes and seconds between sunrise and sunset. This clearly shows that December 21 has the shortest period of daylight. However, the time of sunrise continues to get later and later throughout the whole of December, whereas the time of sunset starts getting later after December 12.  This is good news for Mrs Geek, who walks home from work in the dark at this time of year.

The column in the table showing the solar noon gives the time of day that the Sun is at its highest in the sky or, to put it another way, the middle of the day at the mid-point between the times of sunrise and sunset.  The table shows that, during December, the solar noon moves later and later by about 30 seconds each day.

Why does the solar noon shift ?

solar day is not always exactly 24 hours.  In fact, it is 24 hours only four times a year, and never in December.  The definition of a solar day is the period of time between solar noon on one day and solar noon on the next day.  It is at its shortest, around 23 hours 59 mins 38 seconds, in mid September and at its longest, around 24 hours 30 seconds around Christmas Day.

.

The graph above shows how the length of a solar day differs from 24 hours. The y-axis shows the difference between the length of a solar day and 24 hours on a given date measured in seconds. So, for example,  a value of 10 means  a solar day is 24 hours 10 seconds long , 20 means  a solar day is 24 hours 20 seconds long , -10 means  a solar day is only 23 hours 59 minutes 50 seconds long.

As you can imagine, it would be complete chaos if our clocks and watches had to cope with days of different lengths, so we use 24 hours, the average over the whole year, for all timekeeping purposes (See Note 1).

So, as I mentioned before, the solar days in December are on average 24 hours and 30 seconds, while our clocks and watches are still assuming that each day is exactly 24 hours.  This causes the day to shift about 30 seconds later each day,  as shown in the diagram below.  This explains why the evenings start drawing out before the shortest day, but it continues to get darker in the mornings until the new year.

Sundials and the “equation of time”

Before the invention of accurate clocks sundials were widely used to keep time.

Sundial in Harrogate in the North of England

As the length of a solar day varies over the course of a year, the solar time, which is the time given by a sundial, will not be the same as the time measured by a clock which assumes that all days are exactly 24 hours long. Before the invention of accurate clocks in the 17th century because the variation is so small virtually everyone in the world, apart from a very small number of astronomers, would have been unaware of this.

However, in the eighteenth and nineteenth century as mechanical clocks started to take over timekeeping from sundials, the difference between the time measured by an accurate clock which is called mean time and solar time became an issue for everyday life. Astronomers call this difference ‘the equation of time’.  It was first  calculated and measured by the British astronomer John Flamsteed (1646-1713) in 1673.

Incidentally Flamsteed was appointed by the king as the first British Astronomer Royal in 1675, for which he was given the allowance of £100 per year.  He also set up the Royal Observatory at Greenwich, shown below.

The diagram below shows how the equation of time varies throughout the year.

As you can see from the diagram, if we were to use a sundial to measure time

• from 15 Apr to 13 June and 1 Sept to 25 December to the sundial would be fast
• from 25 December to 15 Apr and 13 June to 1 September the sundial would be slow.

The days when the differences are greatest are

• November 3/4 when at 11:44 am, a sundial in London would be showing a time of 12 noon
• February 11/12 when at 12:14 pm a sundial in London would be showing a time of 12 noon. See Note 2

Why does the length of a solar day vary ?

The reason why the length of the solar day varies is due to two different factors.

1. The fact that the Earth moves in an elliptical (oval-shaped) orbit around the Sun and its speed varies, being faster in earlier January, when it is closer to the Sun and slower in early July, when it is further away.
2. The fact that the axis of the Earth’s rotation is tilted.

The combination of these two factors gives the equation of time shown in the picture above. For more details on how these two factors work together to vary the length of the day, see my post September 18 the Shortest Day.

What about the southern hemisphere ?

In the southern hemisphere the longest day is around December 21. What happens  is that the Sun starts rising later before December 21, but it doesn’t start getting dark earlier in the evening until well after December 21. This is illustrated in the table below, which shows the sunrise and sunset times for December for Wellington in New Zealand, which lies at a latitude of roughly 41 degrees South.

Note 1

The Earth’s rotation  is slowing down, causing the length of a day to get gradually longer. In the year 1900 a mean solar day was 24 hours long. Now, in the early 21st century, a mean solar day is actually 24 hours 0.002 seconds long. To prevent the day we measure using accurate clocks  from drifting away from the “natural day” we need to add an second called a leap second ever few years. For more information on this see my post: The Days are Getting Longer.

Note 2

For most places in the world the Sun isn’t at its highest in the sky at 12 noon. This is because, rather than each area having its own local time, the world is divided into time zones, which are normally a whole number of hours ahead of or behind Greenwich Mean Time (GMT). For example, Manchester, where Mrs Geek and I live, is roughly 2.5 degrees West of Greenwich, but is on the same time zone. Because it is further West, the Sun rises and sets later than it does in Greenwich.  From late Oct to late March, in Manchester the Sun  is at its highest in the sky at 12:10 pm (on average) compared to 12-noon at Greenwich.  At the end of March the UK puts its clocks forward by one hour, so from late March to late October the Sun will be (on average) at its highest in the sky at 1:10 pm in Manchester.

## Akatsuki – a second chance – Updated (7 Dec 2015)

This an update to my original post from 4 December.

In a press release today the Japanese space agency JAXA confirmed that the smaller rocket motors had fired as planned and the Akatsuki is now in orbit round Venus.  The announcement (http://global.jaxa.jp/press/2015/12/20151207_akatsuki.html) went on to say:

“The orbiter is now in good health. We are currently measuring and calculating its orbit after the operation. It will take a few days to estimate the orbit, thus we will announce the operation result once it is determined.”

This is great achievement for the Japanese space programme and hopefully the spacecraft will provide us with many exciting discoveries about Venus.

The image shown above was taken by Akatsuki in ultraviolet light on 7 December 2015, just after it went into orbit around Venus. It shows far more detail of  the cloud patterns in the planet’s upper atomosphere than can be seen in visible light.

Original post below

On 7 December 2010 the Japanese spacecraft Akatsuki (named after the Japanese word for dawn) arrived at Venus after a six month journey.  It was only the second spacecraft launched since 1989 to visit the Earth’s sister planet and, if it had succeeded in orbiting Venus, it would have had been a tremendous boost for the Japanese space programme.

Launch of Akatsuki in May 2010 – Image from Wikimedia Commons

Unfortunately, when it arrived at Venus its main engine failed to fire properly to slow the spacecraft down and put it into orbit, so it shot past the planet and went into orbit around the Sun.

Venus as seen from Earth – Image from NASA

However all was not lost. Other than the main engines, all parts of the spacecraft turned out to be fully functioning, and the Japan Aerospace Exploration Agency (JAXA) will get a second chance to get Akatsuki into orbit when it passes close to Venus on Monday 7 December. This is very unusual for spacecraft which fail to go into orbit. Normally when a major mishap like this occurs the space agency doesn’t get a second chance.

How will the spacecraft get into orbit if its main engine has failed?

The thrust or force provided by rocket motors is usually measured in units called newtons, usually abbreviated to N. The main engine which failed to fire had a thrust of 500 N. To get the spacecraft into orbit JAXA will need to fire 4 of the 8 small rocket motors which were only designed to finely tune the spacecraft’s position. Each of these small motors only generates 20 N thrust  and they will have to fire for a total of nearly 21 minutes to slow down the spacecraft to allow it go into orbit, something they were never designed to do. It is also fortunate that, unlike most spacecraft, the small rocket motors and the faulty main engine of the spacecraft use the same fuel, a liquid called hydrazine.  If this was’t the case then this rescue operation would be impossible.

What will the spacecraft achieve?

Assuming the spacecraft successfully gets into orbit around Venus it has a whole host of instruments which will return useful data. Some of these are listed below:

• a special camera to study lightning flashes, which it will do when on the night side of Venus
• an instrument to study the structure of high-altitude clouds to enable us to understand more about Venus’s weather
• an ultraviolet camera to study the distribution of specific atmospheric gases such as sulfur dioxide in ultraviolet light, a form of light invisible to the naked eye
• an infrared defector which will peer through Venus’s atmosphere to see heat radiation emitted from Venus’ surface rocks and will help researchers to spot active volcanoes, if they exist.

Let’s all keep our fingers crossed for a success on December 7!

Artists impression of Akatsuki orbiting Venus – Image from JAXA

## Akatsuki – a second chance – 7 December 2015

On 7 December 2010, after a six month journey, the Japanese spacecraft Akatsuki (named after the Japanese word for dawn) arrived at Venus after a six month journey.  It was only the second spacecraft launched since 1989 to visit the Earth’s sister planet and, if it had succeeded in orbiting Venus, it would have had been a tremendous boost for the Japanese space programme.

Launch of Akatsuki in May 2010 – Image from Wikimedia Commons

Unfortunately, when it arrived at Venus its main engine failed to fire properly to slow the spacecraft down and put it into orbit, so it shot past the planet and went into orbit around the Sun.

Venus as seen from Earth – Image from NASA

However all was not lost. Other than the main engines, all parts of the spacecraft turned out to be fully functioning, and the Japan Aerospace Exploration Agency (JAXA) will get a second chance to get Akatsuki into orbit when it passes close to Venus on Monday 7 December. This is very unusual for spacecraft which fail to go into orbit. Normally when a major mishap like this occurs the space agency doesn’t get a second chance.

How will the spacecraft get into orbit if its main engine has failed?

The thrust or force provided by rocket motors is usually measured in units called newtons, usually abbreviated to N. The main engine which failed to fire had a thrust of 500 N. To get the spacecraft into orbit JAXA will need to fire 4 of the 8 small rocket motors which were only designed to finely tune the spacecraft’s position. Each of these small motors only generates 20 N thrust  and they will have to fire for a total of nearly 21 minutes to slow down the spacecraft to allow it go into orbit, something they were never designed to do. It is also fortunate that, unlike most spacecraft, the small rocket motors and the faulty main engine of the spacecraft use the same fuel, a liquid called hydrazine.  If this was’t the case then this rescue operation would be impossible.

What will the spacecraft achieve?

Assuming the spacecraft successfully gets into orbit around Venus it has a whole host of instruments which will return useful data. Some of these are listed below:

• a special camera to study lightning flashes, which it will do when on the night side of Venus
• an instrument to study the structure of high-altitude clouds to enable us to understand more about Venus’s weather
• an ultraviolet camera to study the distribution of specific atmospheric gases such as sulfur dioxide in ultraviolet light, a form of light invisible to the naked eye
• an infrared defector which will peer through Venus’s atmosphere to see heat radiation emitted from Venus’ surface rocks and will help researchers to spot active volcanoes, if they exist.

Let’s all keep our fingers crossed for a success on December 7!

Akatsuki orbiting Venus – Image from JAXA

## The Steady State Theory

This post, the latest in my series about cosmology, the study of the origin and evolution of the Universe as a whole, talks about the Steady State theory. This is an elegant alternative theory to the Big Bang, which was very popular among astronomers in the 1950s, although it has now been discarded.

What is the Steady State Theory?

The Big Bang theory states that the Universe originated from an incredibly hot and dense state 13.7 billion years ago and has been expanding and cooling ever since. It is now generally accepted by most cosmologists. However, this hasn’t always been the case and for a while the Steady State theory was very popular. This theory was developed in 1948 by Fred Hoyle (1915-2001), Herman Bondi (1919-2005) and Thomas Gold (1920-2004) as an alternative to the Big Bang to explain the origin and expansion of the Universe. At the heart of the Steady State theory is something called the Perfect Cosmological Principle which states that the Universe is infinite in extent, infinitely old and, taken as a whole, it is the same in all directions and at all times in the past and at all times in the future.  In other words, the Universe doesn’t evolve or change over time.

The theory does, however, acknowledge that change takes place on a smaller scale.  If we take a small region of the Universe, such as the neighbourhood of the Sun, it does change over time because individual stars burn up their fuel and die, eventually becoming objects such as black dwarfs, neutrons stars and black holes.  The Steady State state theory proposes that new stars are continually created all the time at the rate needed to replace the stars which have used up their fuel and have stopped shining. So, if we take a large enough region of space, and by large we mean tens of millions of light years across, the average amount of light emitted doesn’t change over time. See Note 1.

The Sun will last for about 5-6 billion years before it runs out of fuel. Image from NASA

How does does this work with the expanding Universe ?

The Universe is composed of galaxies, each of which contains many billions of stars. Our Milky Way is a large galaxy and is believed to contain over 400 billion stars.

What the Milky Way would look like from a great distance. Image from NASA

As discussed in my previous post, it has been known since 1929 that the Universe is expanding, which means that when we look at distant galaxies they appear to be moving away from us. The further away a galaxy is from us, the faster it appears to be moving away. This relationship, which is known as Hubble’s law, is shown in simplified form in the diagram below.

The horizontal x-axis gives the distance from Earth, and the vertical y-axis gives the speed.  The astronomer Hubble (who discovered the expansion of the universe) plotted a sample of galaxies on the graph accordingly.

Hubble proved that the galaxies are all moving away from each other, which implied that the average distance between galaxies in increasing and so the Universe must be changing over time.

The Steady State theory gets round this by assuming that new matter is continuously created out of nothing at the incredibly small rate of 1 atom of hydrogen per 6 cubic kilometers of space per year. See Note 2. This new matter eventually forms new stars and new galaxies and, if we take a large enough region of the Universe, its density, which is the amount of matter in a given volume of space, doesn’t change over time. If we take two individual galaxies then their relative distance will get further and further apart due to to the expansion of the Universe. However, because new galaxies are being formed all the time, the average distance between galaxies doesn’t change. This is shown in a simplified form in the diagram below.

In the diagram above I have taken a small region of space and marked two galaxies with a red dot and a green dot to allow them to be identified. All the other galaxies are marked with a white dot. Then the upper part of the diagram shows the Big Bang theory where the distance between all the galaxies increases as the Universe expands. In the Steady State theory, shown in the lower part of the diagram, the distance between  the red and the green galaxies  increases but extra galaxies are created so the average distance between galaxies doesn’t change. Indeed if the Steady State theory were true then an observer would measure the same values of:

• the average density of the Universe,
• average distance between galaxies,
• average brightness of galaxies
• how the speed that galaxies are moving away varies with their distance

at all points in the Universe whether the observations refer to 10 trillion years in the past, now, or 10 trillion years in the future.

The origin of the Universe

One of the elegant features of the Steady State theory is that because the Universe is infinitely old the question of its origin doesn’t arise. It has always existed. Unlike the Big Bang theory, the Steady State theory has no point far back in time  when a ‘creation event’ occurred causing the Universe to come into existence. To Fred Hoyle, who was a committed atheist, this was an attractive point of the theory.

Evidence against the Steady State theory

The Steady State theory was very popular in the 1950s. However, evidence against the theory began to emerge during the early 1960s. Firstly, observations  taken with radio telescopes showed that there were more radio sources a long distance away from us than would be predicted by the theory.  By a long distance, I mean billions of light years. Because of the times it takes light to reach us then, when we look at objects billions of light years from us, we are looking back billions of years in time.  So what these observations were saying is that there were more cosmic radio sources billions of years ago that there are now. This would suggest that the Universe is changing over time which contradicted the Steady State theory

Another piece of evidence which emerged to discredit the theory emerged in 1963, when a new class of astronomical objects called quasars was discovered. These are incredibly bright objects which can be up to 1,000 times the brightness of the Milky Way, but are very small when compared to size of a galaxy. Quasars are only found at great distances from us, meaning that the light from them was emitted billions of light years ago. The fact that quasars are only found in the early Universe provides strong evidence that the Universe has changed over time.

A quasar.  Image from ESO

However the real the nail in the coffin of the Steady State theory was the discovery in 1965 of the cosmic microwave background radiation. This is a weak background radiation which fills the whole of space and is the same in all directions. In the Big Bang theory this radiation is a relic or snapshot from the time the Universe was young and hot and was predicted long before it was discovered. However, in the Steady State theory it is almost impossible to explain the origin of this radiation.

Is the Steady State theory a good theory?

For the reasons given above, by the early 1970s the Steady State theory was no longer accepted by the vast majority of  cosmologists. The Big Bang theory is now generally believed to explain the origin of the Universe. However, despite this it can still be argued that the Steady State theory is a good theory.

In the words of Stephen Hawking:

‘the Steady State theory was what Karl Popper would call a good scientific theory: it made definite predictions, which could be tested by observation, and possibly falsified. Unfortunately for the theory, they were falsified’ (Ref 1).

Image from NASA

Further reading and related posts

This post is the sixth in my series about cosmology. A few other posts in this series are:

(1) The Universe Past, Present and Future. This describes what is meant by the Universe and gives an overview of its origins, evidence for its expansion and discusses briefly its ultimate fate. To view this post click here.

(2) A brief history of the Universe.  This gives a history of the Universe from just after the big bang until the current date. To view this post click here.

(3) Dark Energy. This post gives the reasons why cosmologist believe dark energy exists and why it makes up nearly 70% of the mass of the Universe. To view this post click here.

(4) Dark Energy over Time. This post  discusses how the amount of dark energy in the Universe has varied over time and its implications on its future evolution. To view this post click here.

(5) Dark Matter. This post discusses evidence for dark matter, the mysterious substance which makes up around 25% of the mass of the Universe. To view this post click here.

(6) The ultimate fate of the Universe. To view this post click here.

Science Geek Publications

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Notes

1 A light year is the distance that light travels in a year. 1 light years is equal to 9.46 trillion km . The nearest to the Earth, other than the Sun, lies 4.2 light years away.

2  To continuously create matter and to drive the expansion of the Universe. Fred Hoyle introduced into the Steady State model something he called the C-field, where C stands for creation.

References

## Ultimate Fate of the Universe

This post, which is the latest in my series on cosmology, is about the ultimate fate of the Universe, a subject which has engaged scientists, philosophers and religious leaders for centuries. There are many possible endings to the Universe, but the outline I will present here, which is sometimes called “The Big Freeze”, is the most commonly held view based upon the known laws of science.

4 billion years in the future – Milky Way and Andromeda merge

As readers of my previous posts will recall, the Sun is one of around 400 billion stars in the Milky Way galaxy and the Milky Way is one of over 200 billion galaxies in the observable Universe (ref 1). Our galaxy, together with the large spiral galaxy in the constellation Andromeda and around 50 smaller galaxies form a collection of galaxies called the the Local Group.

The Andromeda galaxy – the nearest large galaxy to the Milky Way. It lies 2.5 million light years, roughly 25 million trillion km, from Earth.

As readers of my previous post The Universe Past, Present and Future will recall, the Universe is expanding and, in general, the further away a galaxy is from us the faster it appears to be moving away from us. This does not apply to the galaxies in the Local Group. In fact, the Andromeda galaxy is moving towards the Milky Way at about 400,000 km/h and the Milky Way and Andromeda are expected to collide in about 4 billion years time. When this happens, a large new single galaxy will be formed.  The new galaxy which will be formed by the merger is sometimes called Milkomeda (ref 2) and, over billions of years, it will gradually absorb the other Local Group members.

When this merger occurs it is unlikely than any stars within either galaxy will collide directly because the distances between stars is so great, but the clouds of gas found between stars will collide and merge.

120 billion years in the future – all galaxies too far away to detect

Outside the Local Group the expansion of the Universe will continue. As discussed in a previous post, this will be driven by dark energy. The  speed that a galaxy is moving away from us depends upon its distance. As a galaxy moves a greater distance away from us, then the speed at which it moves increases. When it moves so far away that it is travelling faster than the speed of light we can no longer see it. This is shown in the table below.

This table shows how the distance of  a nearby galaxy which is now 10 million light years away from us (about four times the current distance of Andromeda and thus well beyond the Local Group) increases with time. The last column shows how fast this galaxy is moving in units of kilometres per second. 1 kilometre per second is 3,600 km/h.

In about 105 billion years time, this galaxy would have moved out to a distance of 14.7 billion light years and would be moving away from us at a speed 301,700 km/s, which is more than 1 billion km/h. However, the speed of light is around 300,000 km/s and, because this galaxy would be moving faster than the speed of light, its light would not be able to reach us and it would no longer be visible. See Note 1. In fact, in 120 billion years time, all galaxies outside the Local Group will have moved so far away that the light from them will be unable to reach us.

In the diagram above, the furthest distance than a galaxy can be away from us but still remain observable (in principle) is marked with the red circle.

• The left hand side of the diagram shows the situation today with all galaxies outside the Local Group moving away from us. but plenty of galaxies still visible. The diagram is greatly simplified because there are actually 200 billion galaxies in our observable Universe.
• The right hand side of the diagram shows the situation in 120 billion years time when all galaxies have moved outside our observable Universe.  By this time Milkomeda will have absorbed all the Local Group galaxies.  So if there are any astronomers around, at this distant point in the future, the entire observable Universe will consist of a single galaxy, Milkomeda.

1-10 trillion years in the future – the dark era.

As described in a previous post, stars consume hydrogen to produce helium and later on towards the end of their lives they make heavier elements. New stars are being created all the time from clouds of gas and dust. Many of the beautiful glowing nebulae seen through telescopes consist of glowing gas and dust clouds lit up by newly formed stars.

The Orion Nebula, a region of star formation

However the supply of hydrogen is finite and in about 1 trillion years time there won’t be enough hydrogen left to forms any more new stars (Ref 3). In about 10 trillion years the longest lived stars which are small faint stars called red dwarfs will have come to the end of their lives.  All stars which started life with an original mass less than 10 times the mass of the Sun, which is over 97 % of all stars, will have become very dense cold objects called black dwarfs. Very massive stars more than 10 times the mass of the Sun will have become neutron stars or black holes:

• Neutron stars are super dense objects in which the mass of a star is concentrated in a object about 10 km in diameter. A neutron star is so dense that 1 litre of its material would weigh 500 billion tons.
• Black holes are objects in which the gravity is so strong that once an object enters a region around the black hole called the event horizon it cannot escape. Much has been written about black holes by popular science and science fiction writers. For a good overview I would recommended the article by Stephen Hawking article which can be found at http://www.hawking.org.uk/into-a-black-hole.html

A black hole

None of these object emits any light so the observable Universe in 10 trillion years will be very dark and very cold, having a temperature a fraction above the lowest possible temperature which physicists call absolute zero. It will consist of black dwarfs, neutron stars and black holes, planets and other smaller bodies associated with them. At the centre of Milkomeda will be a large black hole many millions times the mass of the Sun.

10-100 quintillion years in the future – Milkomeda shrinks

(1 quintillion is a million trillion or 1,000,000,000,000,000,000.)
Milkomeda will consist of  objects which are all in motion with respect to each other. Occasionally these objects will get close enough to each other so that their trajectories change slightly. When this happens the speed of one object may speed up and the other may slow down. This is essentially the same effect that spacecraft which visit the outer planets use.  The Voyager space probes, for example, took energy from Jupiter’s orbit to slingshot them into the outer solar system and beyond.

After a number of such collisions an object may get enough energy to escape from Milkomeda. Over a vast period of time, around 100 quintillion years, this will cause the galaxy to gradually shrink as dead stars and possibly their attached planets escape, and the remaining objects would be more tightly bound.

100,000-1,000,000 quintillion years in the future -Gravitational radiation causes objects to fall into a massive black hole

In 1916 Albert Einstein predicted the existence of gravitational waves. One object orbiting another will emit something called “gravitational radiation” causing it to lose energy and spiral slowly inwards towards the more massive object. It is generally accepted by astrophysicists that gravitational waves do exist, although they are incredibly difficult to detect and, despite astronomers looking for them for decades, they have never been observed.

Assuming Einstein’s theory is correct, then also assuming that the Earth has survived the Sun’s red giant phase (which is unlikely) and that it not been detached from the Solar System by a near collision with a passing star (which almost certainly will happen if we wait long enough), in 100,000 quintillion years time it will spiral down to the surface of the Sun (see note 2). It also means that, over an even longer timescale of about 1,000,000 quintillion years, the eventual fate of all the massive objects which have not escaped from the galaxy is to fall into the super massive black hole which lies at its centre.

Next Post

In my next post in this series I will talk about even longer timescales. What will eventually happen to the black hole at the centre of Milkomeda?  And what is the eventual fate of the objects which have not fallen into this super massive black hole?

Related Posts

This post is the sixth in my series about cosmology. The other posts in this series are:

(1) The Universe Past, Present and Future. This describes what is meant by the Universe and gives an overview of its origins, evidence for its expansion and discusses briefly its ultimate fate. To view this post click here.

(2) A brief history of the Universe.  This gives a history of the Universe from just after the big bang until the current date. To view this post click here.

(3) Dark Energy. This post gives the reasons why cosmologist believe dark energy exists and why it makes up nearly 70% of the mass of the Universe. To view this post click here.

(4) Dark Energy over Time. This post  discusses how the amount of dark energy in the Universe has varied over time and its implications on its future evolution. To view this post click here.

(5) Dark Matter. This post discusses evidence for dark matter, the mysterious substance which makes up around 25% of the mass of the Universe. To view this post click here.

Notes

1 This distances in this table should be considered as approximate only and it assumes that the rate of expansion of the universe will not vary with time in the future, which may not be the case.

2 In fact the Earth would be broken apart by tidal forces due to the remnant Sun’s gravity before it hit the remnant Sun’s surface.

References

1 Cain, F (2013) How Many Stars are There in the Universe?, Available at:http://www.universetoday.com/102630/how-many-stars-are-there-in-the-universe/(Accessed: 19 February 2015).

2 http://phenomena.nationalgeographic.com/2014/03/24/scientists-predict-our-galaxys-death/

3 Barrow, J D and Tipler F J. The Anthropic Cosmological Principle 1996 pp641. ISBN 0-19-282147-4.