Category Archives: Amateur

Mysterious Tabby’s Star dims again: observations needed

Let’s face it: KIC 8462852 (also Tabby’s Star or Boyajian’s Star) is a weird star. Since its unusual light variations were discovered by citizen scientists using data of NASA’s Kepler space telescope in September 2015 many, many things have been written by professional and amateur astronomers, science communicators and “searchers of mysteries”, as an interesting hypothesis about its behavior was that it could be signs of activity associated with intelligent extraterrestrial life constructing a Dyson swarm. Of course, this just run wild in general media, and many astronomers since them have been asked by journalist to talk about “Mysterious Tabby’s Star”.

In particular, this theme soon captured the attention of some of my friends at the Instituto de Astrofísica de Canarias (IAC, Spain), as they weekly produce an amazing ~2h science communication podcast Coffee Break: Señal y Ruido (Signal to noise). I’m proud to participate in this podcast from time to time, remotely from Sydney. Coffee Break: Señal y Ruido is, at the moment, one of the most important science communication podcasts in Spanish, with tens of thousands of listeners every week, and broadcasted weekly in several radio stations in Spain and South America.

Well, as the “core” of Coffee Break: Señal y Ruido are IAC astronomers, they decided to submit an observing proposal to get time to obtain spectroscopic data of Tabby’s star using the 1.2m Mercator Telescope, located at the Roque de los Muchachos Observatory (La Palma, Canary Island, Spain). The proposal is led by Marian Martínez González, with Héctor Socas-Navarro, Andrés Asensio, Carlos Westendorp and Carlos González in the team. They got time last week, and were observing till last Wednesday night. They did a great job in social media (please follow @pcoffeebreak) under the hashtag “CB_Tabby“, explaining how observations are conducted in professional telescopes and the results they were obtaining on the fly.

On Sunday night, observations were already showing “something weird” happening again in Tabby’s star. These features were detected by spectroscopy, no photometry. They contacted the very same Tabetha S. Boyajian (Tabby), the initial study’s lead author, who is leading an international follow-up of the star. She sent this message to her collaborators alerting of the weird behavior in Tabby’s star:

And indeed follow-up observations continued during the week. Last night, Friday 19th May 2017, the alert of confirmed by other telescopes: Tabby’s star had dimmed 3%!! This is the plot obtained by The Las Cumbres Observatory Global Telescope (LCOGT) network:

Plot showing the relative brightness of Tabby’s star with time, obtained by Las Cumbres Observatory Global Telescope network. The lowest point shows a 2% drop.
LCOGT

This LCOGT plot shows the brightness of Tabby’s star relative to the star’s normal brightness: the lowest point shows a 2% drop! Tabetha S. Boyajian (Tabby) triggered the alert:

Many media, including Sky and Telescope, New Scientist and Popular Science, have included the news in the last few hours, that is also running wild in social media. But none of these are saying that the actual alert comes from the observations lead by Marian Martínez González (IAC) and “Coffee Breakers” at the 1.2m Mercator Telescope at the beginning of the week! I really think this is not fair, and proper credit to the team that actually triggered the alert at the beginning of the week must be given.

Now, professional astronomers are triggering the “targets of opportunity” to observe Tabby’s star with small and big telescopes. But amateur astronomers are also invited to contribute too!

Star KIC 8462852 in infrared (2MASS survey) and ultraviolet (GALEX). Credit: Infrared: IPAC/NASA, Ultraviolet: STScI (NASA). File from Wikipedia: https://commons.wikimedia.org/wiki/File:KIC_8462852_in_IR_and_UV.png

KIC 8462852 or Tabby’s Star is a 11.7 magnitude star visible with telescopes larger than 5 inches (130 mm) in a dark sky. It is located in the constellation Cygnus (hence, it is visible for all the Northern hemisphere and part of the South hemisphere, although a bit too low for latitudes below 20 degrees south). If you have an equipment that allows to get accurate photometry using several broad-band filters and are interested on contributing to real scientific observations, please don’t hesitate: try to observe KIC 8462852 these days.

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Milky Way rising, LMC, and AAT

Milky Way rising, LMC & AAT

Milky Way, Large Magellanic Cloud, and Anglo-Australian Telescope. Combination of. 6  frames, each of 30 seconds, CANON EOS 5D Mark III, 16mm, f/2.8, ISO 1600. Thursday 2 March 2017. The dome was illuminated in one of the frames by a car leaving the building.

More sizes and high-resolution image in my Flickr.

Credit: Ángel R. López-Sánchez (AAO/MQU).

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Almost full moon and Sydney Tower

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A 97.8% illuminated moon rises over Sydney on Sunday 13th November 2016. I checked for a nice spot to get the photo of this almost full moon (with a supermoon happening tomorrow) crossing behind the famous Sydney Tower.

The image was taken at 7:15pm Sydney time (8:15 UTC) using my CANON EOS 5D Mark III with a 70-200 mm lens at 200mm, f4.5, 100 ISO and 1/800 seconds. The Moon was at a distance of 355 806 km and had an apparent size of 33.6 arcmin. It was only 17 degrees over the horizon.

More info and high resolution images:

https://www.flickr.com/photos/angelrls/30651527540/

Credit: Ángel R. López-Sánchez (AAO/MQU)

Supermoons

During the last few days the news are talking about the “Supermoon” happening on Monday 14th November. The reports (some examples here, here and here) say that “it will be the brightest Full Moon in years“. Even we at the Australian Astronomical Observatory have been asked about this “very rare phenomenon“. But how much is true about all of this?

Let’s take a look. First of all we should have clear that the Moon, as any other small body moving around a larger body, has an elliptical orbit.

Diagram explaining the movement of the Moon around the Earth. Not in scale. Credit: Ángel R. López-Sánchez. Moon image: Paco Bellido.

Diagram explaining the movement of the Moon around the Earth following an elliptical orbit and defining the perigee and the apogee. Not in scale. Credit: Ángel R. López-Sánchez. Moon image: Paco Bellido.

Planets also move around the Sun following elliptical orbits, as it was discovered by the great astronomer (and the first real astrophysicist in History, although he also had to work as an astrologer to get a salary) Johannes Kepler at the beginning of the 17th century.

This means that sometimes the Moon is closer to the Earth and sometimes it is farther from the Earth, just depending on where it is located within its orbit. The point on the Moon’s orbit closest to Earth is called the perigee (at an average distance of 362 600 km) and the point farthest away is the apogee (at an average distance of 405 400 km). On average the Moon-Earth distance is about 382 900 kilometers.

Therefore, just because of its distance, the apparent size of the Moon is a bit larger than usual when it is at the perigee, while it seems a bit smaller than usual when the Moon is at the apogee. An image can explain this much better than words:

Comparison of the apparent size of the Moon when it is located at the perigee (left) and when it is at the apogee (right). Credit: Paco Bellido.

Comparison of the apparent size of the Moon when it is located at the perigee (left) and when it is at the apogee (right). Credit: Paco Bellido.

These photos were taken by the Spanish astrophotographer and friend Paco Bellido in 2014 and 2015 from Córdoba (Spain), my natal city, and clearly show the different apparent size that the Moon has at the perigee (left) when compared to where it is at the apogee (right).

What does happen when the full moon coincides with the perigee? Well, that is a supermoon! The next time this will occur is next Tuesday, 15th November, 12:52am Sydney time. In that moment the Moon will be ~13% larger and ~30% brighter than a full moon happening in the apogee (a “micromoon“). From Sydney (and Australia) the best moment to see it will be on the evening of Monday 14th November, and actually many people are planning to enjoy watching the “supermoon” appearing over the Pacific Ocean at the dusk from Sydney’s famous beaches and clifts.

Regarding this, it is important to say that our brain tricks us when observing the Moon or the Sun close to the horizon: they do appear to be larger than they do higher up in the sky. This is called the Moon illusion, some studies suggest that the perception is that the Moon is almost 3 times larger near the horizon that when located near the zenith.

Supermoon over Espejo's Castle (Córdoba, Spain) on 20th March 2011. This photo, taken by Paco Bellido, has been widely used in many places since then. Now people still try to get it too with their cameras... More info (in Spanish) in "El beso en la luna". Credit: Paco Bellido.

Supermoon over Espejo’s Castle (Córdoba, Spain) on 20th March 2011. This photo, taken by Paco Bellido, has been widely used in many places since then. Now people still try to reproduce this photo with their cameras when full moon… More info (in Spanish) in Paco’s blog “El beso en la luna“. Credit: Paco Bellido.

However, I must insist that the term “supermoon” does not come from Astronomy but from the pseudoscience of astrology. Perhaps that is one of the reasons why many people are talking about this. The term “supermoon” was coined by the US astrologer Richard Nolle in 1979, who defined it as ‘a New or a Full Moon that occurs when the Moon is at or near (within 90% of) its closest approach to Earth in its orbit’.

Nolle, who associated supermoons to catastrophes without any scientific evidence that this was true, didn’t know that we astronomers already had a scientific term to describe this alignment: the perigee-syzygy of the Earth-Moon-Sun system. The word “syzygy” means a perfect alignment between three bodies, that are in a perfect straight line. The most famous examples of syzygies are the lunar and solar eclipses, when the alignment of the Sun, Earth and Moon happens on the lunar nodes (the two points where the plane of the orbit of the Moon around the Earth and the plane of orbit of the Earth around the Sun intercept).

As other “expressions”, such as “blood moon” (a lunar eclipse) or “blue moon” (the second full moon within the same calendar month), the term “supermoon” has become very popular lately, perhaps also because all the action in social media. But these definitions are not official astronomical terms. Indeed, a “blue moon” does not have a proper astronomical definition, and may happen or not depending on the time zone the observer is located.

In any case all the excitement about the supermoon happening on Tuesday 15th (for us in Sydney, but for the majority of the world on Monday 14th) it that the exact moment of the full moon (12:52 am Sydney time) is really close to the perigee, happening at a distance of only 356 536 km from us. The supermoon was not that close since 26th January 1948, when it was at 356 460 km, and it will not be that close till 26 November 2034, when it happens at 356 472 km.

Check the numbers, please. 356 532 km, 356 460 km, 356 472 km… they all just differ in tens of kilometers! That is only a difference of a 0.02% ! Even considering the distances happening on other supermoons (I forgot to say we typically have 2-3 supermoons per year, last 17th October and next 13 Dec will be also supermoons), the differences are just within around 500 km, what is translated into a difference of only 0.14%.

Illustration: Supermoons: can you see what is the largest? Eight supermoons between 2015 and 2018, images have been scaled to the apparent size of the Moon considering its distance from Sydney when the full moon is happening. The dates are times indicated are the moment of the Full Moon. The sizes and distances are computed assuming the observer is located in Sydney, Australia. This is an illustration, not real photos taken from Sydney (I can't travel to the future!). The original Moon image is the photo of the "micromoon" that Spanish astrophotographer Paco Pellido took on 5 March 2015 from Córdoba, Spain, which is the image I use in this post. An image without labels can be found here. The high resolution image is available here. Credit: Ángel R. López-Sánchez, Moon Photo Credit: Paco Bellido.

Illustration: Supermoons: can you see what is the largest? Eight supermoons between 2015 and 2018, images have been scaled to the apparent size of the Moon considering its distance from Sydney when the full moon is happening. The dates are times indicated are the moment of the Full Moon. The sizes and distances are computed assuming the observer is located in Sydney, Australia.
This is an illustration, not real photos taken from Sydney (I can’t travel to the future!). The original Moon image is the photo of the “micromoon” that Spanish astrophotographer Paco Pellido took on 5 March 2015 from Córdoba, Spain, which is the image I use in this post. An image without labels can be found here. The high resolution image is available here. Credit: Ángel R. López-Sánchez, Moon Photo Credit: Paco Bellido.

Let me say it again: the difference of the distance between the Earth and the Moon during a “supermoon”, with these happening typically 2-3 times per year (for full moon, 4-5 times per year in total including new moon), is only the 0.14%. Do you think you’ll be able to notice this with your naked eye?

However, giving numbers (talking quantitatively) the media can say “it is a rare event, the closest supermoon in almost 70 years“. But in practice you’ll not notice a thing. It will be a supermoon essentially similar to all of those we have every year.

Distance from the observer to the Moon depending on when rising or setting (top) or when it is near the zenith (bottom). Credit: Ángel R. López-Sánchez. Moon image: Paco Bellido.

Distance from the observer to the Moon depending on when rising or setting (top) or when it is near the zenith (bottom). Credit: Ángel R. López-Sánchez. Moon image: Paco Bellido.

There is more. Besides the lunar illusion, the moon is actually a bit further away from us when it is rising or setting than when it is near the zenith, as the image above clearly shows. The difference on the distance between the observer and the Moon may vary between few thousand an twelve thousand kilometers. This is called “diurnal effect” as it is, indeed,  larger than the difference of few hundreds of kilometers found for supermoons. In both cases, I insist, the differences on the apparent size of the Moon can’t be noted with the naked eye.

Here again it is important to have a bit of critical thought about what all of this means. In any case this “supermoon” is a great excuse to forget about our domestic problems, look at the sky and be amazed by all the beautiful things that are hiding among the stars.

More info:

PS: Ah, yes, a curiosity:  it is me who will be observing at the Anglo-Australian Telescope (AAT) the night of Monday 14th till Tuesday 15th… That is, quantitatively talking this will be the worst night since the AAT was built to be observing there…

Update 17 November:

I’ve included the illustration comparing the size of the Moon for 8 supermoons, as seen from Sydney. This started as a game in social media on Monday. I also prepared this illustration showing the sizes of the 12 full moons in 2016, as seen from Sydney. Do you identify the micromoon and the 3 supermoons?

Illustration: Full Moons in 2016 as seen from Sydney. All the full moons in 2016, scaled in size following the Moon's apparent size as seen from Sydney. The micromoon corresponds to 22nd Apr (top right) and the thre supermoons are 16 Oct, 14 Nov (15 Nov Sydney time) and 14 Dec. This is an illustration, not real photos taken from Sydney (I can't travel to the future!). The original Moon image is the photo of the "micromoon" that Spanish astrophotographer Paco Pellido took on 5 March 2015 from Córdoba, Spain, which is the image I use in this post. The image without labels is here. A high resolution image is available in my Flickr. Credit: Ángel R. López-Sánchez. Moon photo credit: Paco Bellido.

Illustration: Full Moons in 2016 as seen from Sydney. All the full moons in 2016, scaled in size following the Moon’s apparent size as seen from Sydney. The micromoon corresponds to 22nd Apr (top right) and the thre supermoons are 16 Oct, 14 Nov (15 Nov Sydney time) and 14 Dec. This is an illustration, not real photos taken from Sydney (I can’t travel to the future!). The original Moon image is the photo of the “micromoon” that Spanish astrophotographer Paco Pellido took on 5 March 2015 from Córdoba, Spain, which is the image I use in this post. The image without labels is here. A high resolution image is available in my Flickr. Credit: Ángel R. López-Sánchez. Moon photo credit: Paco Bellido.

Podcast in FBI radio: The Milky Way is missing

Some few months ago I was interviewed by Zacha Rosen in the FBi’s Not What You Think radio show. I was talking about what a galaxy is, the feeling of seeing the center of the Milky Way close to the zenith for the first time, and the problem of the light pollution.

Radio interview in FBI Sydney

The show was broadcasted on FBI 94.5 FM at 10:30am Saturday October 22nd, Sydney time. It is also available as podcast from the Not What You Think webpage or using iTunes.

You can also listen to the 18 minutes interview here:

 

Thanks Zacha for this wonderful experience I hope to repeat in the future!

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Perseids 2016 over Teide Observatory

Perseids 2016 over the Teide Observatory. Combination of  25 meteors from the Perseids meteor shower detected in 24 frames. All frames were taken with a CANON EOS 5D Mark III with a Samyang 14mm lens, 30 seconds exposure at f/2.8 and ISO 800. Frames were taken between 0:00 and 2:30 UTC 12 August 2016 from the Teide Observatory (Tenerife, Canary Islands, Spain). The central dome is the Carlos Sánchez Telescope (TCS). The building at the right is the Quijote Experiment. The towers at the left belongs to the Solar Telescopes at site. The dome of the MONS Telescope is seen with some orange light.

The frame taken at 0:36 UTC was used for showing the landscape and the star field. The Moon was up, its light painted the landscape and buildings. In the background some light pollution from Santa Cruz de Tenerife and La Laguna can be seen (orange colours). The light pollution was enhanced because of the existence of dust in the atmosphere.

The estimated ZHR (Zenithal Hourly Rate) using these images is ZHR = 31 meteors/hour.

More info and high resolution images:

https://www.flickr.com/photos/angelrls/27722628870

Credit: Ángel R. López-Sánchez (AAO/MQU)

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Milky Way over the GTC and the TNG

Milky Way over the 10.4m Gran Telescopio CANARIAS (GTC) and the 3.6m Telescopio Nazionale Galileo (TNG), Roque de los Muchachos Observatory, La Palma, Canary Islands, Spain.

Single frame, 15 seconds exposure at 1600 ISO over CANON EOS 5D Mark III, F=33mm and f/2.8. Taken on Wed 3 Aug 2016, 20:35 UTC.

More info and high resolution images:

https://www.flickr.com/photos/angelrls/27722628870

Credit: Ángel R. López-Sánchez (AAO/MQU)