Low-Energy Astrophysics

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Welcome to Low Energy Astrophysics, an online community of green-minded astronomers who are concerned about various aspects of human energy consumption. We formed in spring 2009 in order to compile a white paper for the Decadal Survey of US Astronomy and Astrophysics, and we used this wiki to write it. After the paper's submission, we converted the wiki to serve as a repository for all kinds of resources that astronomers can use to help them reduce their own energy consumption, and then, crucially, tell all their friends about it.

If you too are a green-minded astronomer, you should join us!

Once you have an account you can chip in with your own ideas, resources, calculations, news etc - to get an account, email dr.phil.marshall at gmail.com.

Add your name to the growing list here, and help us collect more data on how much energy we use in our work.

Also, to be kept up to date with news and so on, join the mailing list here: http://groups.google.com/group/LEastro


Resources for Astronomers

You can find more information on climate change, renewable energy and so on linked to here. Please do add to this page!

AAS Sustainability Committee

Current membership

Please visit the new AAS Sustainability Committee website!

The Astro2010 White Paper

The final paper PDF is available from astro-ph/0903.3384; this wiki's URL is provided in the "comments" field of the astro-ph listing. The sections of the paper have been converted into sub-pages linked to below.

Splinter Session at the 219th AAS Meeting (January 2012, Austin, TX)

A description of the AAS 219 Splinter Session of the AAS Sustainability Committee.

Special Session at the 218th AAS Meeting (May 2011, Boston, MA)

A description of the AAS 218 Special Session of the AAS Sustainability Committee.

Splinter Meeting at the 217th AAS Meeting (January 2011, Seattle, WA)

Agenda and powerpoint slides from the AAS 217 Splinter Session of the AAS Sustainability Committee at the 2011 AAS winter meeting in Seattle, WA.

Splinter Meeting at the 2010 AAS Annual Meeting

Organisational notes and resources for this get-together on the Thursday evening of the 2010 AAS meeting in Washington DC can be found here.

The Energy Consumption of the Average Astronomer

Let's see if we make a more accurate estimate of the energy budget of a professional astronomer, starting from what we did for the white paper.


  • Emphasise energy consumption per day per person; this is the relevant quantity for any exercise in energy accounting. Our chosen units are kWh/day/astronomer. We use the size of the membership of the AAS - 7000 as a rough estimate of the total number of astronomers in the US.
 Calculations go in boxes like this one
  • Start your contributions with your name (e.g. Nicola, Ken H.)
  • Flag problematic areas in bold, and do the discussion on the "discussion page"
  • Keep the results up to date on this page!


 Non-astronomical Energy Consumption:   250 kWh/day/astronomer

 Small-scale, Computationally-intensive Office Work:   4 kWh/day/astronomer

 Observatories:   15 kWh/day/astronomer

 Supercomputing Centers:   1 kWh/day/astronomer

 Travel:   113 kWh/day/astronomer


It is not so easy to compile accurate estimates of energy consumption. It is much easier to find out the financial cost of a project (in USD) than its true cost (in kWh)! You can discuss the concept of true-cost accounting here.

Nevertheless, even from our highly-simplified picture, we can see certain economies of scale in play: operating large ground-based facilities is not as energy-consuming as one might have expected, when averaged over the whole astronomical community. Despite its simplicity, our toy model does allow us to draw quite a strong conclusion: if we are looking to reduce our energy consumption, we can have by far the biggest impact by decreasing the amount of energy we spend on flights.

 Adding up the approximate contributions we have identified above in our toy model,
 we estimate the additional total energy consumption of the average US astronomer at work to be
   (4+7+8+1+113) ~ 133 kWh/day/astronomer.

Astronomy is a small profession. What impact are we having on US national energy consumption?

 Taking the population of the US to be 300 million, we find that astronomy costs
   133 kWh/day/astronomer * (7000 / 3e8) = 0.003 kWh/day per US citizen.

The cost of doing astronomy is a miniscule proportion (0.0012%) of the total US energy budget. We conclude that the energy price per citizen of doing astronomy is negligibly small. The entire daily energy consumption of US astronomy is roughly equivalent to that used by the 1.6 million motorists of Los Angeles in half a minute of their daily commutes.[1]

Do you think that the above non-astronomical energy consumption calculation is unfair, because you walk or cycle to work? Follow this link!

How Does This Relate To Our Carbon Footprint?

Many websites, articles, and advertisements quote the impact of energy consumption in terms of pounds of CO2 produced, rather than kWh used. How do we convert between the two? The EPA has a handy table which shows the carbon dioxide emissions and total electricity generation from 1998 and 1999. (If somebody finds newer numbers, please update them!) We note that coal is the dirtiest source of electricity, emitting 2 pounds of CO2/kWh, but we only get 50% of our electricity from coal. Fully 30% of our electricity is from nonfossil-fueled sources such as nuclear, hydro, solar, wind, etc. The rest is from natural gas, which emits less CO2/kWh than coal. Meanwhile, petroleum also emits a lot of CO2, so each kWh from your car is equivalent to getting the energy from a coal-fired plant. Averaging everything together:

 For U.S. electricity, we emit 1.3 pounds of CO2/kWh.
 For cars, planes, and diesel trains we emit 2.0 pounds of CO2/kWh.

Some energy-consuming activities will have higher carbon footprint than others, when, for example, deforestation is taken into account - follow this link for more details on the conversion between energy consumption and carbon footprint in some specific cases.

Things We Can Do to Reduce Our Energy Consumption

We made some recommendations in the white paper - we can refine and expand these here. Follow the bold links to sub-pages where you can add your ideas and discuss them:

Better Meeting Organisation
Hold conferences in sensible places! Novel funding models that encourage use of trains and buses! 2-center workshops! Coordination of back-to-back conferences!

Replace Flights with Virtual Meetings
Invest in a polycom! Install and use virtual world software! Help develop it so that it works for astronomy! Organise a virtual meeting and shout about it!

More Energy-Efficient Infrastructure
Turn off your computers! Push for individual thermostats! Pressure your building designers! Read more about the Gemini Observatory Green Initiative

Local Sustainable Energy Generation
Buy some solar panels! Look for green options on your electricity bills! Install a wind turbine! Give electricity back to the grid!

Offset Schemes
Do they work? Could one be made to work?

Get The Numbers Right
Write to AAS, NSF, IAU, DoE, NASA... someone should be doing all these calculations for astronomy properly! In the meantime, you can get your own numbers right - there is a range of energy and carbon footprint calculators available online, or you can figure your budget out yourself from scratch. Follow this link to get started

Amplification Through Outreach

The benefits of implementing any of our recommendations can be amplified greatly by publicizing them effectively. The IAU's goals for the International Year of Astronomy 2009 include "bring[ing] the issues of natural environment and energy preservation to the agenda of decision makers."[2] We hope this spirit continues into the next decade, with astronomers playing a role in bringing the issue of energy efficiency to the attention of the public. The astronomy community can directly influence a group of people roughly 30 times larger than itself. A social epidemic needs an efficient network: we sincerely hope that astronomers will be key nodes in this network! Read more about how this works here.

Why Are We Doing This?

Like all workers, we astronomers consume energy while at work. A report on the state of any profession would be incomplete without some consideration of its energy consumption: the way the world uses energy is precipitating a global environmental and economic crisis, the threatening ramifications of which are now coming to light. These include:

  • Potentially catastrophic climate change
  • The depletion of fossil fuel reserves (and the resulting economic and political upheaval)

The UN Intergovernmental Panel on Climate Change (2007) has recently warned of "large-scale climate events [that] have the potential to cause very large impacts,"[3] and current research projects a 10% chance of devastating warming of more than 7oC over this century if no action is taken.[4] The 2007/2008 UN Human Development Report sees climate change as "the greatest challenge facing humanity at the start of the 21st Century," and notes that "failure to meet that challenge raises the spectre of unprecedented reversals in human development." [5] In 2004, the AAS called for "peer-reviewed climate research to inform climate-related policy decisions, and, as well, to provide a basis for mitigating the harmful effects of global change."[6] Many scientists, including the authors of this paper, have come to the conclusion that the mitigation of the harmful effects of climate change needs to start as soon as possible. It is clear that this mitigation must necessarily involve rapid and severe reductions in our production of greenhouse gases, the most crucial of which being the carbon dioxide produced by burning fossil fuels.[3]

Finding alternatives to fossil fuels has other benefits. Oil, for example, is a finite resource highly valued for more than just its combustion: it is the raw material for plastics, pharmaceuticals, coatings, reagents, and many other products upon which we depend daily. Conserving oil addresses this issue, and both of those given above, but meeting this challenge will require a rethinking in the way we live and work, and an active pursuit of wiser alternatives. Let us briefly put this challenge into perspective by assessing the total energy consumption of Americans, and what it would take to supply them with sustainable energy from the brightest astronomical source, the Sun.

 For the United States, per capita energy consumption has been estimated as 250 kWh/day/person,[7][8]
 including household electricity use, manufacturing, and transportation. Suppose we could supply all
 of this energy using electricity from solar power generators, which we might expect to provide
 30 W/m^2 on average.[7]  How much sunny desert land would we need?
 For 300 million Americans, the answer is:
    3e8 x 250 kWh/day/person / 24h/day / 0.03 kW/m^2 = 1.0e11 m^2
 which is 40,000 square miles, or about a third of the area of the state of Arizona.

This calculation is not a comment on the feasibility of solar power generation: it is simply an echo of the conclusion of MacKay (2008)[7] and others that sustainable energy generation for an entire nation requires national-scale infrastructure. The inevitable change to sustainable energy will be expensive, but the less we use, the less we will have to spend.

The amount of energy that the US astronomical community uses is negligible - astronomy is not the problem! However, per astronomer, we use comparable amounts of energy in our work to high-flying businesspeople. Here's the point: all of us in the US must act to reduce our energy consumption. The big, important things that astronomers in the US can and should do are much the same as the things that everyone else can and should do - the key difference is that we astronomers can do them in the public eye. The fact that astronomy is a high-profile activity, receiving more media attention than most (if not all) branches of science, means that the US astronomy community can and should play a leading role in the reduction of energy consumption.

Number of unique visitors to this page since 2009-12-09: Image:/

  1. ^ Los Angeles Dept. of Transportation, "2008 Transportation Profile" http://ladot.lacity.org/pdf/PDF10.pdf
  2. ^ International Year of Astronomy 2009: Goals and Objectives (http://www.astronomy2009.org/general/about/goals/)
  3. ^ 3.0 3.1 Climate Change 2007: The Fourth Assessment Report of the IPCC (http://www.ipcc.ch/ipccreports/ar4-wg2.htm)
  4. ^ Sokolov, et al. (2009) (http://globalchange.mit.edu/resources/gamble/)
  5. ^ UN Human Development Report (2007/2008) (http://tinyurl.com/5nthf8)
  6. ^ American Astronomical Society Endorsement of AGU Statement on Climate Change (http://tinyurl.com/bxwuzf)
  7. ^ 7.0 7.1 7.2 MacKay (2008): Sustainable Energy without the Hot Air (http://withouthotair.com)
  8. ^ UN Human Development Report (2007/2008) (http://hdrstats.undp.org/countries/data_sheets/cty_ds_USA.html)

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