Castle Point Astronomy Club
1969-2019 - 50th Anniversary Year
Castle Point Astronomy Club Diary
April 2019 by Dave Stratton

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Wednesday 3rd April 2019

Mike introduced Gary Auker for his talk: NASA's Human Mars Mission Plans

Gary said that he used to work for E2V and knew a couple in the audience, but had moved to Airbus about five years ago.

He began by telling us about the hazards of the journey both to the astronauts and Mars itself with the transfer of bacteria from Earth to Mars and of course alien stuff back to Earth.

During the trip the travellers will be exposed to radiation which comes from the Sun and galactic radiation. The Russians had a shorter trip where they only stayed for a few days then returned whilst the Americans favoured a much longer stay. The American way was better as the exposure was similar in both with much longer stay for the American idea.

He outlined the differences between the two planets pointing out that Earth’s land area was the same as Mars due to most of its surface being covered by water.

He recapped Martian trips since 1976, 1997, 2004 and 2012 and plans for 2020. We saw pics of the various rovers that have grown vastly in size.

The plan is to bring samples back and this involves super hygiene. We saw a pic of a lunar astronaut just got back in to the base station whose suit was covered in dust – the astronaut said he could taste its metallic taste. It will be quite a task.

NASA Astronauts have a career limit of how much radiation they can experience and a mars mission is much more hazardous that a Moon mission.

Another serious issue is loss of bone density – an astronaut operating in zero G will experience more loss in a month (1 - 2%) than an elderly person on Earth will lose in a year (1 – 1.5%).

Gary showed a chart that indicated the journey times dependant on the relative positions of Earth and Mars. He showed us a chart indicating the various rockets and their capabilities for past present and future. Faster rockets will of course mean less exposure to radiation.

Gary advised us about Deep Space Gateway (DSG) which is a space station orbiting the Moon that will be a stepping stone for deep space exploration.

Apparently the Trump administration has made it clear that it wants Americans back on the Moon.

Gary said that the drive is currently to bring down the costs of space exploration. Private enterprise of people like Elon Musk with his reusable rockets have made very large advances. We saw a chart that indicates that today’s costs are very much lower than when things got started in the 1960s.

Gary finished by emphasizing that the prime reason for space exploration is to find and develop a long term survival strategy for humans if needs must in the future.

Watch this space.

Wednesday 17th April 2019

Mike reminded us that it was just two weeks to our 50th Anniversary celebration.

Ted advised that the Village Fair as on 13th July.

Jim said he was very keen to lend members a telescope.

Mike introduced Ed for his talk on: Observing Highlights for April, May and June

Ed began by saying that last week an asteroid was seen passing close to a star in Bootes. Pallas is the second asteroid to have been discovered and is one of the largest asteroids in the Solar System. With an estimated 7% of the mass of the asteroid belt, it is the third-most-massive asteroid, being 10–30% less massive than Vesta. It is 512 kilometres in diameter.

He put up a star chart showing the area on view in the near future.

He pointed out M3 a wonderful globular cluster.

He said Mars was in the West as a 4 arc second disc. Too small to allow detail to be noted.

On 21st June Mars would be close to Mercury but low in the sky.

From 19th to 23rd May Jupiter and Saturn would have the Moon passing them. Jupiter would be at opposition on 10th July and Saturn on 9th.

Ed showed a nice image of the moon pointing out Copernicus - a lunar impact crater located in eastern Oceanus Procellarum. It was named after the astronomer Nicolas Copernicus. It typifies craters that formed during the Copernican period in that it has a prominent ray system. He said it was best viewed when near the terminator and did a demo with a torch and an egg box to show how the shadows enhanced the features. He added that it was formed by a large impactor and was as big as Essex. Due to the smaller diameter of the moon it is probable that the walls will not be visible from the centre. He showed a sketch giving details of the crater.

He showed a pic of Nicolas Copernicus he was a Renaissance-era mathematician and astronomer who formulated a model of the universe that placed the Sun rather than the Earth at the centre of the universe.

Ed showed us a pic of M81 and M82 which are close enough to get in the same frame pointing out their location from the Plough. NGC 3077 and 2976 are nearby.

Messier 3 is a globular cluster of stars in the northern constellation of Canes Venatici. It was discovered on May 3, 1764, and was the first Messier object to be discovered by Charles Messier himself. Messier originally mistook the object for a nebula without stars.

Porrima is a binary star system in the constellation of Virgo. It consists of two almost identical main sequence stars at a distance of about 38 light years. We saw a sketch Ed did in 2012 where the two were ‘touching’ but now they can be separated.

He finished by handing out a sheet showing the Moon for us to take away.

Mike thanked Ed and introduced Andy for his talk: What’s a brown dwarf and how do we know when we’ve seen one?

Most brown dwarfs are only slightly larger than Jupiter (10–15%) but up to 80 times more massive due to greater density.

A brown dwarf is a type of sub stellar object occupying the mass range between the heaviest gas giant planets and the lightest stars, having a mass between approximately 13 to 75–80 times that of Jupiter, or approximately 2.5×1028 kg to about 1.5×1029 kg.

Below this range are the sub-brown dwarfs (sometimes referred to as rogue planets), and above it are the lightest red dwarfs. Brown dwarfs may be fully convective, with no layers or chemical differentiation by depth.

Unlike the stars in the main sequence, brown dwarfs are not massive enough to sustain nuclear fusion of ordinary hydrogen to helium in their cores. They are, however, thought to fuse deuterium and to fuse lithium if their mass is above a debated threshold of 13 MJ and 65 MJ, respectively. It is also debated whether brown dwarfs would be better defined by their formation processes rather than by their supposed nuclear fusion reactions.

Stars are categorized by spectral class, with brown dwarfs designated as types M, L, T, and Y. Despite their name, brown dwarfs are of different colors. Many brown dwarfs would likely appear magenta to the human eye, or possibly orange/red. Brown dwarfs are not very luminous at visible wavelengths.

There are planets known to orbit brown dwarfs: 2M1207b, MOA-2007-BLG-192Lb, and 2MASS J044144b.

At a distance of about 6.5 light years, the nearest known brown dwarf is Luhman 16, a binary system of brown dwarfs discovered in 2013. HR 2562 b is listed as the most-massive known Exoplanet (as of December 2017) in NASA's Exoplanet archive, despite having a mass (30±15 MJ) more than twice the 13-Jupiter-mass cutoff between planets and brown dwarfs.

What a lot we got.

Wednesday 24th April 2019

Mike reminded us that this Saturday is our anniversary celebration.

Martine has a couple of tickets available.

Ed said that next weekend was a possible Wallasea island visit.

Peter said that it was looking to be a clear tonight.

Andrew said that next week Andy is doing a My Day Quiz.

Mike introduced Andrew for his talk: How the Sky Works Part 2

Andrew explained in detail how and why the Moon has phases it actually takes 27 days to orbit us but we perceive it as 29 days because we have moved further around our orbit.

The Moon’s orbit is tilted at 50° to the ecliptic. Where the two paths cross is called Nodes there is the possibility of getting either a solar or lunar eclipse but not very often at this location.

He explained how eclipses work. The Sun and Moon appear the same size in the sky. The sun is 400 times bigger but also 400 times further away. Solar eclipses are only seen by a 30 mile wide strip of the planet, but lunar eclipses are seen everywhere.

The cycle of eclipses is 18.6years long.

He explained that the Moon is tidally linked with Earth so the same face is seen all the time. Because it rotates on its axis in exactly the time it takes to orbit. This is a common situation when two bodies are gravitationally linked. The Earth’s rotation is slowing by the influence of the Moon and eventually it will stop and be tidally linked in the far distant future.

Andrew said that the inferior planets Mercury and Venus are tricky to observe because they are close to the Sun. Mercury in particular can only be seen when it is East or West elongation. Care must be taken as the Sun will always be nearby.

Venus is similar but much brighter and higher in the sky.

The superior planets – particularly Mars have a strange retrograde motion where they appear to move backwards. He explained this in detail. The reason is simply that the Earth is moving faster on its orbit and ‘overtakes’ the slower moving outer planets so we see them from a different perspective.

He then described how to measure the size of things and the distance between them on the sky. Once again the sky is imagined as a dome over our heads with the various objects attached to it. It is 180° from one side to the other and sizes and distances are given in degrees. For example the Full Moon is 0.5° from one side to the other. So is the Sun. Mercury can be up to 28° above the horizon.

Degrees can be subdivied. There are 60 arc-minutes in 1 degree and 60 arc-seconds in 1 arc minute.

The sky rotates at approx. 15 degrees/hour or 15 arc-seconds/second.

Always interesting.

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