Rosetta blog: Chasing a comet from Earth – refurbish on a veteran watching campaign

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An talk with Colin Snodgrass of a Open University, UK, who coordinates a consortium of veteran astronomers watching Comet 67P/Churyumov-Gerasimenko from Earth in support of a Rosetta mission.

Q: Rosetta has been ‘living’ with Comet 67P/Churyumov-Gerasimenko for roughly a year now. How was this year from a viewpoint of a veteran astronomers watching a comet with telescopes on Earth?
A: It has been a really sparkling year for everybody in comet science, following a formula from Rosetta, though thankfully a ground-based perspective of 67P didn’t get too sparkling nonetheless – a comet mostly followed a predictions in terms of a sum brightness, that is calming as it allows us to have certainty in a skeleton for watching (and for Rosetta). We watched a comet grow from a singular dot to uncover a transparent comet-like figure in 2014, and afterwards had a comparatively prolonged winter where we couldn’t observe a comet (between Nov and April). Now that a comet is behind within strech of a telescopes, it is an even some-more considerable sight, with a prolonged tail manifest in deeper images. Recently, as a comet is coming perihelion, it is many some-more active. We can now investigate a gasses and large-scale dirt jets in a coma from ground-based observations.

Recent picture from a 2 m Liverpool Telescope, taken on a morning of 19 Jul 2015. It comprises 10 x 20s r-band images. The length of a tail manifest in a picture in a twilight sky is approximately 120,000 km. Credit: Colin Snodgrass / Geraint Jones / Liverpool Telecope

Recent picture from a 2 m Liverpool Telescope, taken on a morning of 19 Jul 2015. It comprises 10 x 20s r-band images. The length of a tail manifest in a picture in a twilight sky is approximately 120,000 km.
Credit: Colin Snodgrass / Geraint Jones / Liverpool Telecope

Q: How many observatories were concerned and how mostly have they celebrated a comet?
A: In 2014, a comet was still comparatively faint, with a bulk of around 20, approximately 400,000 times fainter than a exposed eye can detect, so many of a observations were achieved with some of a biggest telescopes accessible on a ground: a European Southern Observatory’s Very Large Telescope and a Association of Universities for Research in Astronomy’s Gemini South telescope, both located in Chile. Other observatories were also used, including a TRAPPIST comet-chasing telescope, also in Chile, a Nordic Optical Telescope on La Palma, in a Canary Islands, and a Las Cumbres Observatory Global Telescope Network, that operates robotic telescopes during several locations opposite a globe.

Recent picture of Comet 67P/C-G formed on information acquired from a VLT on 8 Jul 2015, as tweeted by astronomer Alan Fitzsimmons. (see https://twitter.com/FitzsimmonsAlan/status/619113668106711040). Credits: Alan Fitzsimmons / Colin Snodgrass / ESO

Recent picture of Comet 67P/C-G formed on information acquired from a VLT on 8 Jul 2015. Credits: Alan Fitzsimmons / Colin Snodgrass / ESO

Then, from a finish of 2014 and for a initial few months of 2015, a comet was too tighten to a Sun to be celebrated from anywhere on Earth; when veteran telescopes could see it again, in May, it was many brighter than during a finish of 2014, with a bulk around 15. Many some-more telescopes in a northern hemisphere are now apropos concerned in a observations, including a William Herschel Telescope and a Telescopio Nazionale Galileo on La Palma and ESA’s visual belligerent hire on Tenerife, in a Canary Islands, a BTA-6 visual telescope of a Special Astrophysical Observatory of a Russian Academy of Science in a Caucasus Mountains, a Canada France Hawaii Telescope and a NASA Infrared Telescope Facility on Mauna Kea, Hawaii. Some of a colleagues are also watching a comet during x-ray and radio wavelengths with a IRAM and ALMA observatories. We are now following a comet many nights regulating robotic telescopes, including a Liverpool Telescope on La Palma and a STELLA telescope on Tenerife, that have done special efforts to assist a debate – enabling new modes of operation to lane a relocating aim like 67P in a box of STELLA, and even building a totally new spectrograph to be supportive to cometary gasses on a Liverpool Telescope.

Comet 67P/C-G on 22 May taken with a VLT/FORS2 instrument. It is a multiple of 2 x 30s R-band exposures, aligned on a comet. The comet changed opposite a credentials stars between a dual images, heading to double stars in this combination. Credits: Colin Snodgrass / Alan Fitzsimmons / ESO

Comet 67P/C-G on 22 May taken with a VLT/FORS2 instrument. It is a multiple of 2 x 30s R-band exposures, aligned on a comet. The comet changed opposite a credentials stars between a dual images, heading to double stars in this combination. Credits: Colin Snodgrass / Alan Fitzsimmons / ESO

Q: What can we tell from a data? Is a comet working as approaching from a prior perihelion passes?
A: The comet’s large-scale activity is augmenting in good agreement with a predictions from prior observations. However, comets are indeterminate and we contingency always design a unexpected! For this reason, it is generally critical to have a vast network of telescopes concerned in a campaign, so that we can pledge a quick response in a box of any remarkable change to a comet’s behaviour. After perihelion we will also have special ‘target of opportunity’ mode observations ready, that can be triggered on brief notice, usually in box there is a vital outburst during a comet.

One of a other formula that we have from observations so distant is that there is a poignant asymmetry in a comet’s activity – we have usually recently been means to detect a gas in a coma from a ground, though we know that we were means to detect a same gasses many serve from a Sun after perihelion in prior orbits. We will continue to follow a comet via a rest of a extended Rosetta goal to endorse this, and to improved know because this is a case.

Q: Which telescopes will be watching a comet around perihelion?
A: At perihelion a comet is in northern skies, so it can't be seen from a incomparable telescopes in Chile, like a VLT and Gemini South. Our debate moves to telescopes north of a equator, including those in Hawaii (e.g. Gemini North, NASA’s IRTF) and a mainland USA, and European facilities, generally those situated in a Canary Islands. 67P is too tighten to a Sun to indicate a Hubble Space telescope to it until October, though a vast accumulation of telescopes on a belligerent are means to minister – though usually for a really brief duration before morning any night. This is one of a reasons to have telescopes around a universe observing.

Q: What are we looking brazen a many from these observations?
A: As a comet reaches perihelion a activity turn is high adequate that we can detect jets within a coma that are thousands of kilometres in length. These contingency somehow be related with a activity settlement that Rosetta sees during a nucleus, though as nonetheless no one knows how a tiny jets seen in OSIRIS or NAVCAM images (which are usually a few km long) describe to a really large-scale structure seen from ground.

Coming adult on a blog soon: an refurbish on the amateur observing programme and how we can get involved. 

Source: Rosetta blog