November 2021

Planets to look for

Venus is looking glorious in the western sky in the evenings. Because of the way the orbits line up , it is backdropped by the centre of the Milky Way in Sagittarius right now, and in the first week of November its path will take it almost right through the middle, as seen from Earth.

On 4 November it will be extremely close to Sagittarius A*, the black hole at the centre of the Milky Way. This is of course an observational effect, the black hole itself is 26,000 light years away, but you can use Venus as a reference point.

You can also take the opportunity to use the stars of Sagittarius to make ‘the teapot’ (shown here outlined in green), which will help guide you. If the teapot asterism feels a little forced, it’s nothing compared to the centaur that it is supposed to represent.

Venus in Sagittarius on 4 November

Jupiter is still looking nice and bright, high in the evening skies. It reaches eastern quadrature on 15 November, which means at sunset on this date it will lie exactly along a line drawn north to south in the sky. Seen from above, lines drawn from the Sun to Earth and from Earth to Jupiter will meet at a right angle. Another way of thinking about this is if you point one hand at the setting sun and the other at Jupiter, your arms will make a right angle.

Constellation of the month

Aries the Ram

Aries is a medium-sized constellation and part of the Zodiac, meaning that it lies along the ecliptic which you will be able to trace out using the instructions above. It is visible in the northern sky in the mid-evenings during November, and is recognised as the gently curving set of stars representing the ram and its horns.

The brightest star in this constellation is Hamal, a giant star that has used up all the fuel in its core and is now in the process of fusing hydrogen in layers around the middle. The location of fusion away from the core of the star causes its outer layers to heat up and expand, and ultimately cool the star down a little, turning it a reddish colour.

The ram appears in many stories of mythology, perhaps the most well known being the bearer of the golden fleece which was made from its hide, serving as the basis for one of the trials of Jason and his crew of Argonauts. This story is also recorded in the gigantic asterism of Argo Navis, these days broken into the constellations of Vela, Puppis and Carina – visible in the south east at the same time as Aries is up in the north.

Uranus

Always guaranteed to get a lame laugh, this planet gets its name from the primordial Greek God of the Sky. It’s not easy to see, but you can figure out its rough location by tracing the ecliptic across the sky to its position. In exceptionally dark skies you can see it without a telescope but it’s more likely that you will need some equipment to help you out. It should appear as a greenish-blue source through a medium-sized telescope.

Uranus is technically the first planet ever discovered. The other naked eye planets (Mercury, Venus, Mars, Jupiter and Saturn) have been known since antiquity, while Uranus is recorded as being discovered on 13 March 1781. Interestingly, the planet has a long history of accidental observation by people who didn’t quite recognise it for what it was. Its long orbit and great distance from us mean it requires many observations or powerful equipment to see the signs that this point of light in the sky is an entire world.

Uranus’s large tilt of 97.7 degrees is something of a mystery, with possible explanations usually involving a giant collision with planet sized object long ago. No matter how, the result is that seasons on Uranus last for decades at a time.

Uranus presents an almost featureless face to Voyager 2

The local claim to fame is that observations performed at Perth Observatory helped confirm the discovery of the rings of Uranus. The planet was predicted to pass in front of a distant star and block out the light received. Astronomers noticed that in addition to the expected drop in starlight from the planet being in the way, there were also dips in starlight observed just before and just after Uranus blocked the star: tell-tale signs of a ring system around the planet obstructing the starlight.

Images: Elliot and Nicholson

Uranus continues to play an intriguing role in models of solar system evolution.

DART Mission to test planetary defences

It seems like something that belongs in a movie: An asteroid is headed towards Earth – can we deflect it by flying a big heavy spaceship into it to push it off course and save the planet?

NASA takes this question very seriously and is putting the theory to the test with the Double Asteroid Redirection Test (DART) mission launching on 24 November. Taking off on a SpaceX Falcon 9 rocket, it will speed towards the double asteroid Didymos. The mission is fairly simple: fly a 500kg projectile as fast as you can into Didymos’s tiny moon, Dimorphos, and see if it’s orbital velocity can be measurably altered.

To be clear, Didymos and Dimorphos are not on a collision course with Earth, we are safe for now. But astronomers estimate we have found only about 40% of all asteroids larger than 140m across, easily large enough size to destroy a city.

The logic behind this experiment is that if one day we do find an asteroid with Earth’s name on it we could send an impactor to alter the speed of the asteroid. It may only be by a fraction of a millimetre per second (mm/s), but over many years this tiny difference in speed can add up to a significant distance in space and so with enough warning we may cause the asteroid to miss the Earth. That’s the theory, now to put it to the test. Asteroids can be tricky to study, and their widely varying composition makes it difficult to extrapolate data from one study to the next.

Image: DART

And about that rocket

Captain Kirk boldly went where quite a few people have gone before, with William Shatner hitching a ride to space on Blue Origin’s New Shepard rocket. Travelling to an altitude of 110km, this carries travellers well above the Karman line, the internationally agreed edge of space.

You might have noticed that the New Shepard rocket looks a little different to the sleek rockets we have become used to. To quote science communicator Scott Manley: “Rocket design is usually a team effort, which means if you want to churn out an ugly launch vehicle you have to actually assemble an entire team of aesthetically-challenged engineers and have them fight against the natural tendency for rockets to look cool.” So why such a design?

Image: Blue Origin

The reason is in the landing of the rocket and the safety of the people on board. Landing rockets is a difficult and dangerous task, so if you can make sure there are no people around when it happens, all the better.

The crew capsule at the top of the New Shepard is designed to detach and land separately under parachutes as the now uncrewed booster stage lands using its engine. The two separate at an altitude of about 100km so they have plenty of time to drift apart.

Here’s the important thing – the capsule needs to be less aerodynamic than the rest of the rocket so that it falls slower and doesn’t collide with the booster mid-descent. Hence why it has a wide base. The need to be aerodynamic going up and blunt coming down makes the top of the rocket look the way it does. Add in some internet culture and the rest is history.

Other space news

NASA’s Lucy mission launched on an Atlas V rocket bound for the Trojan asteroids to explore the origins of the Solar System.

The Space Launch System launch vehicle for the Artemis 1 mission is finally fully assembled. This mission will carry an uncrewed Orion capsule to the Moon in February 2022 as a test flight for future human missions.

SpaceX conducted a static fire of Starship. Tests like these are vital for validating the hardware before attempting a launch and orbital flight.

A Russian film crew paid a short visit to the ISS to record footage for a movie.

Three Chinese astronauts were launched on a six month mission to the Tiangong Space Station.

It’s musical chairs on the ISS as the SpaceX Crew 3 mission will be launched and Crew 2 return home.

The Ariane 5 rocket successfully launched two communications satellites into geostationary transfer orbit. By itself a fairly standard launch for Arianespace, this mission is significant because it reaffirms the reliability of the Ariane 5 for its next lift off. Hopefully launching 18 December, it will be loaded with probably the most important payload it will ever carry, the James Webb Space Telescope.

Boeing’s Starliner is still beset with problems. Corroded valves caused the postponement of Orbital Flight Test 2 and the company has taken the hit.