James Webb Space Telescope is a million miles from home  

Joseph Bulmer

Stargazing with John Stapleton from Torbay Astronomical Society:

At the time of writing, NASA’s James Webb space Telescope (JWST) is about to enter its stable orbit around the L2 Lagrange point on the Earth’s orbit.

This point is a place in space where all the competing gravitational forces - from the Sun, Moon and Earth - cancel each other out and so offers a very stable position for very little fuel expenditure so the usable life of the telescope is extended as much as possible.

The observing part of the mission is planned to last five months and to cover all of the sky.

It lies nearly one million miles from the Earth; Webb has covered this distance in about 30 days travelling at a cruising speed of 1,255 miles per second.

The James Webb Telescope is usually referred to as a NASA probe but, in fact, it is a joint venture between NASA the European Space Agency, ESA, and the Canadian Space Agency.

The probe is named after James Webb, the first director of NASA in the early 1960s.

He was, apparently, keen to not only fulfil President John F Kennedy’s promise to put a man on the Moon before the decade was out, but also to expand the scope of scientific discovery considered possible with astronautics and remotely operated space probes.

The mission so far has been one of the most complex ever attempted.

Firstly, the telescope was too large to be carried into space by any rocket the Americans are currently using, so it was launched by a modified Ariane rocket from the European Space Agency launch site in Kourou, French Guiana.

The telescope is designed to observe in the visible spectrum and in infra-red wavelengths.

This poses problems for the JWST as, unlike Hubble, which is in Earth orbit, it is never shielded from the damaging heat and radiation from the Sun.

JWST, therefore, carries its own sunshield.

This consists of five layers of hi-tech foil, with each layer only as thick as a human hair and about the same area as a tennis court.

This had to be unfurled and stretched out into its operating position during the journey to L2 without causing any snags or tears in the fabric of the shield. This was successfully achieved.

The temperature on the hot - sunward, but also Moon and Earth - side of the shield ranges from about 12C to 55C  while the temperature on the cold side is between -202C and -210C.

Keeping sensors cold is absolutely critical to the infra-red observations JWST is expected to make.

The next technical problem to overcome was the positioning of the secondary and 6.5 metre diameter primary mirrors.

This was compounded by the fact that the primary mirror is actually composed of 18 separate hexagonal segments which all had to be moved into position individually.

This process took several days, again, en-route to L2. This was achieved.

However, every one of the 18 segments also has to be flexed into the right curved shape which will enable all the segments to come to focus at the same point, thus creating the large mirror.

Even this is not a straightforward task as each segment must be curved in its own unique way.

This process will not be completed until after JWST arrives at L2.

If any of these processes fails or is not completed the telescope will be useless.

JWST is so far away that there can be no service missions such as those that saved Hubble.

The size of the mirror and the sensitivity of the instruments mean that JWST will be able to see things up to 100 times fainter than those observed by Hubble.

This means that we will be able to see cooler, fainter and more distant objects as well as seeing objects already found by Hubble in more detail.

Instruments on the telescope will be able to analyse the atmospheres of exoplanets to study their potential for habitability.

By studying objects at distance of billions of light years we are looking at light - and the image it carries - that left the object billions of years ago so, in this way we are effectively looking back in time and are able to study the early Universe when stars and galaxies were forming.

By studying infra-red images with JWST we will be able to see stars that are newly formed and just barely ignited, and stars that are dying, having used up all their fuel and are cooling down to a black, cinder remnant.

As with all successful advances in observation, astronomy can only benefit as we learn more and more about our Universe.

The Star Chart

The sky will look like the chart on February 7 at 9pm and again on February 21 at 8pm. And four minutes earlier on each successive night e.g. 8.56 on February 8.

To use the chart hold it above your head whilst facing South so that you can look directly from the chart to the sky.

Skynotes

Please note all times given in this article are in GMT and as the clocks have changed that is the current time.

Sun: At the start of the month there are just nine hours of daylight but as February progresses the length of day will increase to almost 11 hours.

Mercury: Mercury is technically visible in the morning sky but rises only half an hour before the Sun and is very low in the sky in a south easterly direction.

Venus: Venus is also a morning object rising about two hours before the Sun throughout the month. This aspect of Venus, being a bright object in either the morning or evening sky was a source of confusion for ancient astronomers. For some time the 'evening star' aspect of Venus was known as Hesperus and the 'morning star' was Phosphorus. It was the ancient Greek astronomers who plotted the movements of the planets who eventually realised that these two and brilliant Venus were one and the same object.

Mars: Mars is now a difficult morning object, rising 90 minutes before the Sun but can be seen five degrees (the distance across your middle three fingers at arm’s length) below Venus at the end of the month.

Jupiter: Jupiter now lies very low in the south west and is no longer easily observed.

Saturn: At the beginning of the month, Saturn is too close to the Sun to be visible and by the end of the month it rises in the morning sky just half an hour before the Sun so is not easily observable.

Uranus and Neptune: Uranus lies due south at 6pm and sets by 1am and is seen against the background stars of Aries and close to the Pleiades star cluster.  At magnitude 5.8 it is visible in binoculars.

Look for a tiny greenish disc compared to the pinpoints which are the stars.  Neptune is seen against the background stars of Aquarius (below the asterism known as the Square of Pegasus) and sets by 8pm.

At magnitude 7.8, it will require large binoculars or a small telescope to find it.

Neptune displays a smaller and truly blue disc compared to that of Uranus although it will appear only as a bluish star to most small instruments

Meteor shower: There are no regular meteor showers this month. However stray or sporadic meteors can still be seen at any time. Some of these can be very bright.

Comet:  Comet C2019/Atlas will pass through the length of the constellation Gemini this month, but it is not expected to become a naked eye object.

The New Moon occurred yesterday, February 2, with First Quarter on February 8, Full Moon then follows on February 16 and Last Quarter on February 23.

Data supplied by Simon Harding, Observations Secretary Torbay Astronomical Society

Diary Dates

The next meeting of Torbay Astronomical Society, complying with the current Covid regulations, will be held at Torquay Boys' Grammar School. On February 17, Dr Diego Altamirano, principal research fellow of the School of Physics and Astronomy at the University of Southampton will be guest speaker. Talks will also be available online via Zoom. For details contact the Secretary TAS on astrosecretary@gmail.com .  Visitors and prospective members especially welcome.

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