Uranus is not as boring as we thought

The conventional view of Uranus has been that its apparent surface shows few, if any, distinguishing features. The images from the Voyager 2 probe in the 1980s showed what Nasa describes as a "placid, solid blue ball".

The James Webb telescope, using infrared wavelengths rather than Voyager's visible ones, shows something else. In this light the north polar ice cap becomes visible. (Uranus, bizarrely, rotates almost at right angles to all the other planets so the north pole is, in this configuration, pointing towards us.) Some storm clouds are apparent as well, and the planet's rings show up clearly.

I've not been adding to this blog of late, so I realise I am a bit late with this as a group of photos were released by Nasa back in December 2023. The Nasa web page has copious information about the set, which includes wider field photographs (also larger than the image above).

That Nasa page doesn't give information about the wavelengths used for the image. There's a more detailed report from Scientific American, which notes that image is built using wavelengths of 1.4, 2.1, 3.0 and 4.6 microns. Since photographically, we're more used to nanometres this means 1400, 2100, 3000 and 4600 nm.

[Image credit: NASA, ESA, CSA, STScI]

Lucky Infrared Images of Jupiter

Back in 2011 I noted some IR shots of outer planets by Mike Brown at Caltech, at a wavelength of 1.5 µm.

Last week another fascinating set of images, this time of Jupiter, emerged. These were at 4.7 µm and rather than a demonic cricket ball this time the infrared image resembled a jack-o'lantern.

This wavelength reveals a glow from relatively warm deeper layers of the atmosphere breaking through upper cloud layers. In visible light this is obscured by even higher haze in the atmosphere. The image here is a composite built from a number of so-called 'lucky' images, captured from earth during brief pauses in our atmospheric turbulence. The instrument was the Gemini North telescope on Hawaii’s Maunakea volcano, at an altitude a little over 4,200 metres.

To find out more, I'll point you at the paper available on the Gemini Observatory web site.

[Image credit: International Gemini Observatory/NOIRLab/NSF/AURA M.H. Wong (UC Berkeley) and team Acknowledgments: Mahdi Zamani.]

Flying high ... for infrared

One of Nasa's longer-running infrared astronomy projects is the Stratospheric Observatory for Infrared Astronomy (SOFIA). It uses a pre-loved 747 with a suitable new aperture to fly high and catch infrared radiation from above 99% of atmospheric water vapour.

Not quite flying your Lear Jet to Nova Scotia for a total eclipse of the sun but still pretty cool.

Read about it on the Scientific American blog.

Spitzer gone ... waiting for Webb

I have to admit that I am not as au fait with what's happening in astronomy these days as I should be; especially since infrared astronomy, once the new kid on the block, is where most of the action now occurs.

The end of January saw the decommissioning of NASA's Spitzer Space Telescope. At about 1430 PDT on Thursday January 30th, JPL reported ...

...the spacecraft was placed in safe mode, ceasing all science operations. After the decommissioning was confirmed, Spitzer Project Manager Joseph Hunt declared the mission had officially ended.

We now have to wait until March next year for the James Webb telescope to launch and the next phase will begin.

NASA's Spitzer Space Telescope Ends Mission of Astronomical Discovery

Infrared astronomy faces a gap

In late 2016 I noted that the James Web infrared space telescope was two years away (in this post) but it now seems that the launch has been pushed back to March 2021 at the earliest. This delay means that there will be a gap in infrared observation capabilities, as the Spitzer is set to cease operation over a year before that.

More information on this can be found on the Scientific American web site.

Two years to James Webb ... and counting

Once upon a time infrared was regarded as being the new astronomy. There was even a book of that title, published in 1975 and written by David A Allen. By 2014, and David L Clements' book Infrared Astronomy - Seeing the Heat, infrared was dominating the field. No longer the new astronomy, now it is astronomy.

As the BBC news web site pointed out, last week marked two years until the launch of the James Webb Space Telescope (JWST). This is the replacement for Hubble, and is a much more powerful/sensitive device. The mirrors and optical components are now assembled and ready to be tested. It's a reflector. Radiation hits the main mirror, 6.5 metres across, is then reflected and focussed onto a much smaller secondary mirror in front of the main one and then reflected onto sensors at the centre of the main mirror. You can see this in the photo above.

The JWST will be sensitive to wavelengths long enough to see back to the early days of the universe. It's basic doppler effect: as the sources of light move away from us at increasing speed, the light we see from them lengthens in wavelength towards red and beyond (hence red-shift). Because the universe is expanding, the further away from us an object is, the faster it is moving away from us. [Good pub question: where is the centre of the observable universe? Answer: where you are.]

This is one of its sensors, for NIRCam - 2048 by 2048 pixels for near infrared wavelengths between 0.6 and 5 microns (600 and 5000 µm).

NIRCam is one of four instruments: NIRCam, NIRSpec, NIRSS and MIRI. MIRI images wavelengths between 5 and 28.5 microns with a resolution of 1024 by 1024 pixels. This is a gross oversimplification, and sections 20 to 23 of Nasa'a scientific FAQ give much more information about the cameras.

If you're interested in more fine detail about the NIR system, then try this NIRCam Instrument Overview paper from the University of Arizona. Nasa has a set of web pages, Explore the James Webb Space Telescope, with copious resources.

[Photos courtesy of Nasa]

Thermal Eclipse

Many thanks to Dr Chris Lavers of the University of Plymouth for sending over unusual views of last week's partial solar eclipse. Here's an example ...

This was taken in the south west of England with a FLIR 320 by 240 pixel E320 thermal imaging camera. This camera covers a range of 7.5 to 13 µm, which includes a substantial atmospheric window around 10 µm.

More snippets

Apologies for not posting yet this year ... but here are a few items to make up for it.

Towards the end of last year I came across a claim that a special diet could extend human vision into the edge of the near infrared.

Petapixel carried an explanation of the research project and also a rebuttal by a neuroscientist. The original crowd-funded experiment page is on experiment.com and the group carrying out the research is called Science for the Masses. Since last August the web seems to have gone quiet on the project.

A slight increase in deep red sensitivity would be useful for astronomers wanting to view the universe at the wavelength of hydrogen-alpha: 656.28 nm. Canon produced a camera modified to give similar better response a few years back and Nikon have now also done so, although theirs is a high-resolution full-frame camera. It's the D810A. The older Canon still had some infrared filtering in place so it couldn't be used for infrared photography, but it is unclear whether this is the case with the Nikon. The press release is unclear although DP Review suggests that there is still filtering.

For those of you interested in the BBC's natural history infrared shooting, there is a training film on line where Colin Jackson explains his technique. However, this his team moved on to using modified Canon DSLR cameras rather than 'pure' video cameras so the film is a little out of date.

Finally, a thermal imaging video showing cloud formations across the earth, shot from space at a wavelength of 6.5 µm. (This is worth expanding for a better view.)

BBC Sky at Night on Infrared

The current edition of Sir Patrick Moore's long-running BBCTV astronomy programme, The Sky at Night, is called Age of the Infrared (follow the link for the schedule). The program abstract says:

Space telescopes such as Herschel and Spitzer are peering at the dusty, dark cosmos and with their infrared eyes they can see the cold parts of the sky where stars are being born. Sir Patrick Moore discusses why the infrared is full of hidden delights, whilst Dr Chris North talks to Dr Amy Mainzer about NASA's infrared WISE telescope.

Origination is Sunday/Monday at five minutes past midnight (later in Northern Ireland) with several repeats on BBC Two, BBC Four and BBC HD. It will be on the iPlayer as well.

American Astronomical Society Austin sees new infrared images

The BBC web site has a small slide show of some far infrared images from space telescopes (such as WISE, Herschel and Spitzer) that were released at the 219th American Astronomical Society meeting in Austin, Texas, which ends today (12th Jan).

Outer planets ablaze at 1.5 microns

Astronomer Mike Brown at Caltech hunts in the outer reaches of the solar system. He usually concentrates on what is called the Kuiper Belt which extends from the orbit of Neptune out to about twice as far as Neptune's orbit. He recently used the Keck telescope in Hawaii with the intention of imaging Neptune's moon Triton, but the views of the planet itself, and closer neighbour Uranus, were too interesting to ignore. The Keck's adaptive optics system, which compensates for turbulence in the earth's atmosphere, produces stunning results.

Neptune, glowing like a demonic cricket ball, shows the two distinct bands which are glowing at the imaging wavelength of 1.5 microns (1500 nm). Of course these are not really 'hot' since the surface of Neptune is -200 C and the bright bands will only be a few degrees warmer. These correspond to faint but visible features on Neptune's 'surface'.

With Uranus the main features are the rings, which stand out distinctly given the low level of radiation from the planet itself, and the spot to the top left which is the moon Miranda. The bright spots on the surface are clouds. This is notable because the 'surface' of Uranus, in visible light, is almost devoid of any features (although, as the 'northern' uranian hemisphere warms up some banding is appearing).

There is more at space.com.

RW Wood took infrared photographs of gas giants Jupiter and Saturn at the end of October 1915. He had been granted use of the 60 inch reflector at Mount Wilson and took photographs through infrared, yellow, violet and ultraviolet filters. His infrared filter had a band-pass of 700 nm, with its upper limit being determined by the plate sensitivity, which was probably less than 800 nm. In this case infrared photographs showed fewer features than visible light whereas belts were clearly shown on the violet and ultraviolet plates. (It is not possible to record a wavelength as long as 1.5 microns using photographic emulsion, so an electronic sensor has to be used, although this is not thermal imaging. However, this wavelength is still within an atmospheric window for infrared.)

You can read Wood's 1916 paper on the SAO/NASA Astrophysics Data System (ADS). It is entitled Monochromatic Photography of Jupiter and Saturn.

[My thanks to Mike Brown for permission to reproduce his images here.]