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In this issue of SpaceTides

Dear SpaceTides Subscribers

The April and May 2007 editions of SpaceTides will be scaled-down versions due to increased work responsibilities on the editor's part for these two months.

Spectroscopy is something not well known in the public eye, although it plays such a fundamental role in astronomy. I've read up on the concept and tried to put it in simple terms in this issue. It's even something that the amateur astronomer can do.

Regards,

Gerrit Penning
Editor

Total subscribers as at 1 April 2007: 739 (+6 from previous issue #52)

1. Spaceflight news from around the world

Artist's concept of the Orion crew vehicle in lunar orbit.

Credit: Lockheed Martin Corp.

The risks in human missions to Mars
Inspired by an article on the NASA.gov website

Using the International Space Station as testbed and building an outpost on the Moon will be critical to prepare for a future manned mission to Mars. NASA is planning to send people back to the Moon, using a new spacecraft called the Orion Crew Vehicle.

Currently there are major risks associated with humans going to Mars. A mission will last a minimum of 3 years due to the positions of Earth and Mars in their orbits. During this time astronauts will face a daunting array of risks, including cancer from harmful solar radiation (even if they wear spacesuits!), bone and muscle loss from a low-gravity environment as well as a possible shortage of oxygen, food and fuel supply.

By performing experiments on the space station, and building a base on the Moon, astronauts and scientists can slowly start to address the above risks to ensure a safe journey to Mars. More risks at spacescan.org

2. Astronomy news from around the world

This image shows the Orion "bullets" as blue features and represents the light emitted by hot iron (Fe) gas. Credit: Gemini

3. The Solar System

The planet Uranus as photographed by the Voyager 2 space probe. NASA

The tilted planet Uranus

Uranus is the 7th planet from the Sun and the 3rd largest in the solar system. It was the first planet to be discovered in modern times, by Sir William Herschel in 1871.

Uranus has a peculiar characteristic: it has an extreme axial tilt. The planet lies virtually on its side, at a 98 degrees angle. Each pole receives 42 years of direct sunlight and then 42 years of total darkness, during the planet's orbit around the Sun.

Uranus's atmosphere is mostly composed of gas and ice. The gas consists primarily of hydrogen, a smaller amount of helium and a much smaller amount of methane. The methane is responsible for giving Uranus its distinct blue colour due to the absorption of red light by the methane molecules. A number of clouds in the upper atmosphere have been observed.

Uranus also has a very faint ring system. It was discovered from Earth in 1977 and was confirmed during the Voyager 2 satellite fly-by in 1986. It consists primarily of 'icy' materials such as water, methane, and ammonia, with higher-density rocky materials deeper in. More at Wikipedia.

4. Sky Observation Log

The Moon over the Karoo, in late March 2007.

Planets - April 2007
Mercury is visible in the morning skies, rising in the constellation of the Fish at about 5h00. Venus shines bright in the evening skies just after sunset in the west. Mars rises in the morning skies in Aquarius at around 3h00. Jupiter can be seen from 22h00 rising below Scorpius. Saturn can be seen in the evening skies, until about midnight, between Leo and Cancer. Uranus and Neptune are morning objects, but you need a binocular/telescope to see them. Anyone seen that pesky little planet Earth? Apparently it's been speeding around a star called "Sun", somewhere near the Orion arm of the Milky Way galaxy. It is wanted for questioning by the galactic police in conjunction with some crazy false UFO reports generated by its inhabitants...

Constellations - April 2007
It's now the time to observe Leo, the larger Lion, in the northern skies in the evenings. Leo lies on its back for us in the southern hemisphere. It looks like an Egyptian sphinx seen from the side. The bright object close to its front paw is the planet Saturn.

The Southern Cross is rising in the south-east. The Pointers (Alpha and Beta Centauri) is situated below it. Above and to the right of Crux you will find the Diamond, actually stars belonging to the constellation Carina. Above the Diamond you will see the False Cross - somewhat larger than the real cross. Seasoned observers should try to see the giant boat Argo in this vicinity, consisting of the 4 constellations Carina, Vela, Puppis and Pyxis. Once you've seen Jason's boat, you may travel with him and his Argonauts to Colchis in search of the golden fleece. Seeing Argo is a challenge, but's its worth the effort.

Deep Sky Objects in Carina for binoculars and telescopes - April 2007
NGC 3372 (Keyhole nebula/Eta Carina). NGC 3532 (Wishing Well open cluster)
NGC 3114 open cluster, IC 2602 (Southern Pleiades). NGC 2516 open cluster

Other celestial events - April 2007

Comet 2007 E2 Lovejoy: a new comet is visible in the southern skies, although in the mornings. It was discovered by the Australian Terry Lovejoy on 15 March 2007, after more than 1000 hours of diligently photographing the night sky.  During April the comet moves northward through Sagittarius and Aquila, and is well placed for observation by binocular. It will most probably not become visible enough for the unaided eye.  The comet makes its closest approach to earth on April 24, when it will still be a morning object, transiting at around 5am. Finder charts: http://www.yp-connect.net/~mmatti/
Lovejoy ephemeris: http://cfa-www.harvard.edu/iau/Ephemerides/Comets/2007E2_1.html

Full Moon on 2 April 2007
New Moon on 17 April 2007

More event information on the ASSA website: http://assa.saao.ac.za and in the 2007 Sky Guide.

Deep Sky Delights for April is now available - discover hidden treasures in the Southern Cross. Download 400 kb PDF.

5. Special Feature: Spectroscopy

Using Spectroscopy to study the Stars

How is it possible that astronomers can tell us what kind of elements stars consist of and how hot they are? We can't even touch it and we haven't even sent satellites there!

Well, it's all about light waves. By analyzing the radiation received from stars, astronomers can use a technique called "spectroscopy" to conclude with accuracy what the stars consists of. They can even tell its temperature, density and motion.

The clue lies in fingerprinting. Each element (e.g. oxygen, hydrogen, helium and other forms of matter) have its own unique spectrum of light, like a fingerprint. Stars consists of these gasses and emit light waves. By using a spectrometer, astronomers can analyze the light waves into its different parts and because each gas gives off a unique spectrum, they can easily tell what kind of gasses are present in the star.

A substance will emit spectral lines (at a particular wavelength) when it is heated, and absorb light at the same wavelength when it is cool. When the substance emits light, an emission spectrum is generated. When the substance absorbs light (at the same characteristic wavelength), the spectral pattern that is formed is called an absorption spectrum.

For example, burning sodium will always produce two very close yellow lines (near the middle of the spectrum) on a black background, and it is the only element that will do exactly this. If you analyze light waves from a star and find these characteristic yellow lines, you know that there was sodium in the star that produced this light. And, if you look at a light source and find dark lines in the same place on the spectrum, you know that the light you're seeing passed through sodium gas somewhere on its journey to you. Obtained from Enchanted Learning.


The unique spectrum of hydrogen gas. Our Sun consists mostly of hydrogen.  The visible layers (the photosphere and the chromosphere) is the only part of the Sun that is cool enough for hydrogen to exist in its atomic form and it is here that we can see the absorption and emission spectra for hydrogen. From: http://www.solarobserving.com/halpha.htm

6. Photo Sense

Photographer: Willie Koorts (SAAO).  Date picture taken: 2 April 2007. Location: SAAO, Sutherland.
Description: "When I went up to the domes at sunset last night, there were thunderstorms almost 360 degrees [around me]. I plonked down my camera on a mini tripod and as it got darker, I could expose for longer and longer, ending up taking sequences of 15 second exposures, in the hope of catching a nice strike with a dome on the foreground." (5 images were stacked in total)

7. SA Astronomy: Scope-X on 21 April 2007

Scope-X in Johannesburg on 21 April 2007
The well-known annual telescope and astronomy expo called Scope-X, organized by the Johannesburg Centre of ASSA, will take place on Saturday, 21 April 2007 in Johannesburg. Download PDF Information brochures in Afrikaans or English by visiting the Johannesburg Centre's website.

Main theme: Astrophotography. International guest speaker Richard Berry from the USA will deliver the keynote talk.  You can also attend a special dedicated workshop on 20 April presented by Richard.