Category: Space Sunday

For parts of East Africa, the Middle East and Asia, the 2020 summer solstice of June 21st was marked by an annular eclipse of the Sun.

Solar eclipses – when the Moon passes between the Earth and the Sun – take a number of forms, of which the most spectacular is, of course, a total eclipse. These occur when the distance between the Earth and the Moon is such that entire disk of the Sun is covered by the Moon, and the Moon’s shadow – called the umbra – falls directly onto the Earth’s surface, reducing the landscape directly below it to a state of dusk-like darkness called Totality. And just before that period of Totality, that can last several minutes, the solar corona is displayed as a beautiful halo of pearly white light.

However, as the Moon’s orbit around the Earth is elliptical rather than circular, for a total eclipse to occur, the Moon needs to be around 379,100 km from Earth. At this distance, the conical shadow of the Moon (the umbra) is sufficient for us to witness Totality. When the Moon is further away from Earth – say at the 381,500 km of the June 21st, 2020 event – , we have an annular eclipse, in which the Moon’s umbra “falls short” of reaching the Earth’s surface. This means that only around 99-99.5% of the Sun’s disk is covered by the Moon when observed along the path of the umbra, leaving the Sun and Moon appearing as a “ring of fire” hanging in the sky. It is this “ring of fire” that makes an annular eclipse the second most spectacular type of solar eclipse.

This particular event began at 03:45 UTC on June 21st, 2020, with the Moon “cutting in” to the disk of the Sun, and ended at 10:34 UTC as the Moon moved clear of the Sun. However, the period of maximum eclipse – the time at which the “ring of fire” might be seen – occurred at 06:54 UTC and was visible along a narrow track of the eclipse path just 21 km wide for around 35-60 seconds. Even so, it was still spectacular for those who witnessed it.

For people north and south of this narrow band of passage, the eclipse varied in nature from a partial ring of fire (where the disk of the Moon is jut off-centre enough relative to the Sun for the ring not to be completed) to a partial eclipse (where the disk of the Moon partially sits between the Earth and the Sun, but leaves a fair amount of the latter visible.

As direct viewing of the Sun is dangerous, ahead of the event, Astronomers Without Borders – a global group based out of the United States – worked with regional governments and astronomical groups and societies in Africa to get 16,000 pairs of solar glasses distributed to help people view the eclipse safely. For those well outside the path of the event who wished to witness it, the eclipse was streamed through You Tube and other platforms by a number of organisations such as SLOOH.

Eclipses are seasonal in nature, and generally occur in pairs: one lunar – when the Earth is between the Sun and the Moon, so that the later moves within the Earth’s shadow. This annular solar eclipse was preceded by a penumbral lunar eclipse on June 5th. However, and somewhat unusually, it will be followed by a further penumbral lunar eclipse on July 4th / 5th. A penumbral eclipse is one where the Moon is only within the outermost extent of the cone of Earth’s shadow, dimming it as it reflects the Sun’s light, rather than blocking sunlight falling on it entirely.

The next pair of eclipses will take place in November / December 2020, with a penumbral lunar eclipse on November 30th and a total solar eclipse visible from Chile and Argentina occurring on December 14th. For now, here’s a video of the June 21st event.

Six Billion Earths?

A new study from the University of British Columbia estimates that there could be as many as six billion Earth-type planets in the Milky Way galaxy orbiting within the habitable zone of stars with the same G_Type spectral class as our own Sun.

This may seem a surprisingly high number, but it requires context. In this case, it is estimated our galaxy has 400 billion stars of which some seven percent are G-Type. This means that if the study’s findings are correct, Earth-type planets orbiting in the habitable zone of G-Type stars averages out as just 0.18 per star.

The study findings are based on extrapolations from the data on 200,000 stars in the Kepler Space Telescope catalogue, with some adjustments to calculations.

The adjustments were required because Kepler used the transit method of exoplanet detection: watching for regular dips in a star’s brightness. However, given that a large planet will cause a correspondingly greater dip in a star’s brightness than one the size of Earth, the Kepler data is naturally biased towards finding larger planets. Further, it is possible that the dips caused by Earth-sized worlds could be mistaken for transient data rather than actual planets. So to handle things, Michelle Kunimoto, one of the researchers in the study used a technique called forward modelling.

I started by simulating the full population of exoplanets around the stars Kepler searched. I marked each planet as ‘detected’ or ‘missed’ depending on how likely it was my planet search algorithm would have found them. Then, I compared the detected planets to my actual catalogue of planets. If the simulation produced a close match, then the initial population was likely a good representation of the actual population of planets orbiting those stars.

– Michelle Kunimoto, University of British Columbia

Continue reading “Space Sunday: a ring of fire, 6 billion Earths and an FRB” →

 

Images of Proxima Centauri (l) and Wolf 359 (r) captured by NASA’s New Horizons spacecraft 7 billion km from Earth, are overlaid against images taken of the two stars from Earth-based telescopes, showing how the stars appear to “move” depending on the viewpoint. Credit: NASA

For the first time in history, a spacecraft has been used to demonstrate parallax as it applies to the stars – and in the process, underlining the fact that the constellations beloved of astrology are little more than a matter of line-of-sight as  seen from Earth.

The spacecraft in question is New Horizons, the mission that performed a fly-by of Pluto in 2016, and which is now some 7 billion kilometres from Earth – far enough to give it a unique view of the heavens around our solar system. On April 2nd/23rd, 2020 the spacecraft was commanded to turn its telescope on two of our nearest stellar neighbours, Proxima Centauri and Wolf 359 (a star doubtless familiar to Star Trek: The Next Generation), some 7.9 light years from Earth, to take pictures of both.

When compared to images of the two stars as seen from Earth, those from New Horizons clearly show how differently the two appear against the background of other stars when seen from different points of observation that are sufficiently far apart.

Use of parallax is a common astronomical exercise, used to measure the distance of stars from Earth. However, up until the New Horizons experiment, the average separation between points of observation have been opposite sides in Earth’s orbit around the Sun – or a mere 297,600,000 km apart when averaged out. That’s far enough to allow for an accurate measurements of other stars, but not far enough to show how differently a star might appear from different points in the sky.

It’s fair to say that New Horizons is looking at an alien sky, unlike what we see from Earth.nd that has allowed us to do something that had never been accomplished before—to see the nearest stars visibly displaced on the sky from the positions we see them on Earth.

– Alan Stern, Principal Investigator, New Horizons

For the experiment, the images from New Horizons were compared with images captured by the Las Cumbres Observatory, Panama, operating a remote telescope at Siding Spring Observatory in Australia, and from the Mt. Lemmon Observatory in Arizona, both of which imaged the stars on the same night as New Horizons captured its images, so as to provide a direct comparison.

Witnessing the Birth of Stars

The Rho Ophiuchi cloud complex is a dark nebula of gas and dust that is located 1° south of the star ρ Ophiuchi in the constellation Ophiuchus. Some 460 light-years from Earth, it is one of the closest and active start-forming regions to the Sun.

It’s called a “dark nebula” because the dust cloud is so dense, visible light from stars within it is almost completely obscured. However, astronomers using the Atacama Large Millimetre/submillimetre Array (ALMA) have found something of interest within the cloud.

The item in question is IRAS 16293-2422, a system that has a long history of being observed in the infra-red. However, it had been thought the system comprised a binary pairing of protostars, simply referred to as A and B some 700 AU apart. However, the new study has revealed that the star known as A is actually itself a pair of stars, now called A1 and A2. They are both of similar in mass to the Sun – A1 being slightly smaller, and A2 around 1.4 times larger, and each is surrounded by its own accretion disk from which it is drawing material.

These stars and their disks have certain fascinating aspects. The first is that they are only separated by a distance slightly greater to that of Pluto when at aphelion relative to Earth. They also complete an orbit around one another one every 360 terrestrial years. In addition, the accretion disks around A1 and A2 are also unique.

Both disks are extremely active, filaments of matter streaming into the stars at the heart of each, and further filaments of dust flowing into the disks from the nebula. In addition, the disk around A2 disk appears to be oddly inclined compared to the disks around A and the more distant B, suggesting complex interactions may be at play around it. The disk also appears to have parts rotating in opposite directions relative to one another, the first time such a phenomenon has been seen in a protostar accretion disk. It suggests that should planets eventually form around the star, those nearer to it may orbit the opposite direction to those further out.

Organic scans of the disk also detected glycolaldehyde — a simple form of sugar – and Chloromethane, also called methyl chloride, an important biomarker, together with Carbon Sulphide, Isocyanic Acid, Formamide, and Formic Acid. The presence of the organics is important as it shown that the basic building blocks of life can exist within the accretion disks around stars, and so may be available when the remnants of that disk forms planets.

It’s not clear if / when the formation of either star may reach a point of nuclear ignition, or how such an event might affect the other. However, their confirmation provides astronomers with a first-hand opportunity to witness the earliest stage in the process of stellar evolution.

Continue reading “Space Sunday: a touch of astronomy” →