Astronomy Tonight

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Below you will find a large form that lets you customize the output data. Its defaults are for Ottawa, the capital of Canada. As a convenience, here are the results for some selected locations (Canada and US only):

The information is customized for your location, and includes:

• current weather conditions and forecast.
• weather radar images (usually not available in the far north).
• satellite images showing cloud cover (not available in the far north).
• the Clear Sky Clock (Canada and the US only).
• positions of the Sun, Moon, and planets.
• selected asteroids and bright comets.
• a current diary of sky phenomena.
• Messier/Caldwell objects appearing above the horizon (highest altitude first).
• a stereographic chart of the entire night sky.
• the current observation window, showing the Sun's rise-set times, times of twilight, and the Moon's rise-set times.
• lunar libration, for today and the upcoming month.
• positions of the Galilean satellites of Jupiter.
• upcoming meteor showers (if any).
• auroral activity level (if above your configured threshold).
• upcoming occultations at your location (if any).
• phenomena related to the Galilean satellites of Jupiter (if any).

These links will help you look up the data you need when filling out the form:

• latitude and longitude: the quickest way is to click the Current location button, which will use your browser's default location. Otherwise, use Google Maps: right-click on a location, and select "What's here?", to see the corresponding latitude and longitude.
• radar id for US locations: use NOAA/NWS.
• clear sky clock: the quickest way is to click the Use lat/long button, and the system will find the station that's nearest to the latitude and longitude location you've already entered in the form. Otherwise, use cleardarksky.com to infer the station id.

If the meaning of an item in the form below is unclear to you, try and hover your mouse over the item; some items have a tooltip. Required items are marked with *.

There is a defect related to time zones. Example: if you are in Ottawa, then you can view data for Washington DC, since those two cities are in the same time zone. If you are in Ottawa and you view data for Los Angeles, however, then the times are going to be messed up. Everything works fine only if you stay in the same time zone used by your browser. Most of the time, this defect won't bother you, because you're usually concerned with nearby locations. (This problem is caused by how Javascript treats dates and times. There are ways around this problem, but I haven't done anything about it yet. If you need a work-around, then just temporarily change your computer's time zone setting.)

The satellite imagery is particularly useful, because it shows detailed cloud information. The satellite image generated by the above form centers on a given location, and has a small area. It's also interesting to see the clouds over a large area of the country. The images are especially dramatic when the Sun is low in the sky, and produces longer shadows. Here's a form for showing larger cloud images.

Credits:

• Astronomical Algorithms, Jean Meeus: many algorithms used here are taken from this book.
• Environment Canada : current conditions, forecasts, and radar images.
• NOAA/NWS : current US weather conditions, forecasts, and radar images.
• NowCOAST: server for NOAA images captured by the GOES satellites (clouds).
• Observer's Handbook of the Royal Astronomical Society of Canada: comments on the Messier objects, and osculating orbital elements for planets.
• My custom star catalog is the source of star positions.
• Allen Rahill (Canadian Meteorological Center) and Attilla Danko: Clear Sky Clock images.
• International Meteor Organization : Meteor shower data.
• British Astronomical Association, Comet section : current comet data.
• Jet Propulsion Laboratory : Orbital elements for asteroids and comets.
• British Geological Survey : position of the geomagnetic north pole.
• NOAA Space Weather : auroral activity (Kp).
• International Occultation Timing Association : occultation predictions.
• US Naval Observatory, Multiyear Interactive Computer Almanac (MICA, v2.2.2) : sky diary, phenomena for Galilean satellites.

This site also allows you to generate a customizable, precise planisphere for your location (as two PDF files).

You can help to improve astronomytonight.net, by contributing to its github repository.

Code last updated on: 2024-01-18.