Astronomy and space tools

Observing 10

Plan the night, find what is up, line up the mount and log what you see.

• Observing session plannerPick the astronomy tools you need for a night (sky tonight, target heights, polar alignment, your telescope, the month's events and a log sheet), see them together on one page, and download them as one image, PDF or Word file, or each on its own. #18
• Sky tonightFor your place and date: sunset, when it gets properly dark, the Moon's phase and rise and set times, where each planet is, and the best galaxies, clusters and nebulae for your eyes, binoculars or telescope. #13
• Light pollution calculatorTurn a sky quality meter reading, the faintest star you can see, a Bortle class or a luminance into all the others, see how much artificial light adds to your sky, and how much longer your images need than at a dark site. #51
• Target altitude plannerPlot how high your targets climb through the night, against your own trees and roofs. Get meridian (pier flip) times, the hours above a useful height, airmass and parallactic angle for one target or a whole list. #14
• Polar alignment helperSee the clock position of Polaris (or Sigma Octantis in the south) for your place and time, drawn on a polar scope reticle, so you can line up your equatorial mount in a minute. #15
• Sky events calendarA month-by-month sky calendar for your place: Moon phases and how much is lit each night, meteor shower peaks, eclipses you can see, planet oppositions and elongations, and equinoxes, with a one-tap calendar file. #16
• Observing logLog what you see at the eyepiece or camera: object, equipment, seeing, transparency and notes. Each time you save, choose a new log file or add to an existing one, so your files grow into a database of every observation. #17
• Eclipse finderList every solar and lunar eclipse you can see from your place for up to 50 years, with local start, peak and end times, how much is covered, the Sun or Moon's height, and a picture you can scrub through. #65
• Dark-sky calendarSee a whole year of nights at once: twilight, true darkness and moonlight for your place, the Moon-free dark hours in each month, and the best nights for deep-sky observing and imaging. #45
• Meteor shower plannerPick a shower such as the Perseids or Geminids and see how many meteors an hour to expect from your place and sky, hour by hour, where the Moon will be, and how much moonless dark time each night around the peak has. #50

Astrophotography 8

Size up your telescope and camera, set exposures and open FITS files.

• Star FWHM checkerOpen a star image and measure every star's FWHM, half-flux radius and elongation, with a map across the field that shows focus, sensor tilt, field curvature and tracking errors. #72
• Image stackerCalibrate your light frames with darks, flats and bias, align them on their stars and stack them with a kappa-sigma clipped average that removes satellite trails. Download the result as 32-bit FITS. #76
• Sub-exposure calculatorFind the shortest sub length that buries your camera's read noise under sky noise, from a test frame or from your sky brightness. Works for one-shot colour, LRGB and narrowband, with a chart of what each length costs. #42
• Backfocus calculatorAdd up your camera, filter wheel, off-axis guider and adapters, allow for the filter's thickness, and get the exact spacer stack to hit your reducer's or flattener's backfocus from the spacers you own. #43
• Mosaic plannerWork out how many panels you need to cover a big target such as the Andromeda Galaxy with your telescope and camera, with the overlap you choose, a picture of the layout, and RA/Dec for every panel centre as a CSV. #49
• Telescope and camera calculatorEnter your telescope, eyepieces and camera to see magnification, true field, exit pupil, faintest stars, image scale and whether your camera suits your seeing, with a picture of what fits in the view. #19
• Star trails and exposure calculatorFind the longest exposure before stars start to trail with your camera and lens (NPF and 500 rule), and plan star-trail sequences: frames, total time and card space. #20
• FITS viewer and header inspectorOpen a FITS image to view it with a proper stretch, read pixel values and sky coordinates, and see its full header. Or drop a whole night's files to list exposure, filter and temperature and total your time per filter. Nothing is uploaded. #21

Planetary science 4

• Mars timeSee the time on Mars now or at any Earth date: Mars Sol Date, Coordinated Mars Time, local mean and true solar time, the rovers' mission sols, the season and the dates of this Mars year's equinoxes and solstices. #53
• Impact crater calculatorWork out the crater an asteroid or comet would dig on the Earth, the Moon or Mars, the energy in megatons and how often such impacts happen, or work back from a crater to the size of the body that made it. #58
• Planet data explorerEvery planet, Pluto and the large moons in one sortable table: compare any two to scale, plot any two quantities (such as Kepler's third law) and see your weight on each world. #74
• Jupiter's moonsSee where Jupiter's four large moons are at any moment, in the same orientation as your eyepiece, and list the coming transits, shadow transits, occultations and eclipses you can see from your place. #62

Solar physics 2

• Sun position calculatorFind where the Sun is at any place and moment: its altitude and azimuth, how long shadows are, sunrise, sunset, solar noon, twilight, a sun path diagram and a year of day lengths. #61
• Sunspot counterOpen a white-light photo of the Sun and the tool finds the disc, the spots and the groups, and gives the relative sunspot (Wolf) number with spot areas. Tap to correct anything it got wrong. #75

Stellar astrophysics 7

• Magnitude and flux converterConvert between Vega and AB magnitudes, Jansky, f_ν, f_λ and photon flux in UBVRI, 2MASS, WISE and SDSS bands or at any wavelength, with the zero points and their sources shown. #44
• Blackbody calculatorType a temperature, a B − V colour or a peak wavelength to get the Planck spectrum, Wien peak, power per square metre and how it splits into UV, visible and infrared; add a radius and distance for a star's luminosity, bolometric correction and magnitudes. #56
• Light curve period finderPaste times and brightness measurements, even with gaps and uneven spacing, and find the period with a Lomb-Scargle periodogram, false alarm probabilities, alias checks and a folded light curve. #48
• Radial velocity orbit fitterPaste a star's radial velocities and fit a Keplerian orbit: period, semi-amplitude, eccentricity, periastron, systemic velocity with uncertainties, the mass function and the companion's minimum mass. #64
• Spectral line identifierPaste a spectrum or a list of wavelengths and match each line to hydrogen, helium, metals, nebular lines, lamps, light pollution or the atmosphere, and find the redshift where several lines agree. #70
• Variable star logLog your variable star estimates or camera magnitudes, see each star's light curve, work out estimates by the step method, and export AAVSO Visual or Extended files ready to upload to WebObs. #77
• Double star calculatorPredict where the companion of a binary star will be, with separation and position angle from its orbital elements, or measure a double star on your own image by tapping the two stars. #68

Galactic and extragalactic astronomy 3

• Cosmology calculatorType a redshift and get the age of the universe then, the lookback time, comoving, angular diameter and luminosity distances, kpc per arcsecond and the distance modulus, for Planck 2018, WMAP or your own cosmology. #41
• Redshift calculatorConvert between redshift, velocity in the relativistic, optical and radio conventions, and observed wavelength or frequency of any common spectral line, with the cosmological recession velocity. #55
• Galaxy rotation curve fitterPaste a galaxy's rotation curve and fit a bulge, an exponential disc and a dark halo: masses with uncertainties, how much of the galaxy is dark matter, and the halo's total mass. #69

Exoplanets 4

• Habitable zone calculatorFind the habitable zone of any star from its temperature and luminosity, and see whether a planet sits inside it, how much starlight it gets, its equilibrium temperature and its orbital period. #52
• Exoplanet mass calculatorTurn a star's radial velocity wobble into the planet's minimum mass (m sin i), or a planet mass into the wobble it causes; add a transit depth for the radius, density and gravity, with the velocity curve drawn. #57
• Transit plannerType a planet's ephemeris and see every upcoming transit with ingress, middle and egress on your clock, the star's altitude, darkness, the Moon, how much you can see and how uncertain the timing is. #54
• Transit light curve fitterPaste an exoplanet transit light curve and fit a limb-darkened model: the planet's size relative to its star, depth, duration, impact parameter, inclination and the star's density. #71

Radio astronomy 3

• Radio telescope calculatorFind what a radio dish or array can detect: beam width, collecting area, gain in K/Jy, system equivalent flux density, noise after any integration, a source's signal-to-noise and how long you need to detect it. #60
• Interferometer uv-coverageLay out an array of radio dishes, pick a source and an observing time, and see the uv tracks Earth's rotation sweeps out, the resolution, the largest scale you can image and the dirty beam. #67
• Hydrogen line analyserPaste a 21 cm hydrogen spectrum from a backyard radio telescope and get LSR velocities, the terminal velocity, kinematic distances, column density and the Milky Way's rotation curve. #73

Spaceflight and astrodynamics 5

• Rocket equation and delta-v calculatorEnter each stage's dry mass, propellant and Isp and get the delta-v of every stage and the whole rocket, the payload fraction, and how it compares with the delta-v needed for orbit, the Moon or Mars. #46
• Link budget calculatorWork out whether a radio link will close: a CubeSat downlink, a ground station or a point-to-point link. Gives EIRP, free-space loss, G/T, C/N0, Eb/N0, the margin, the fastest data rate and the margin through a satellite pass. #59
• Orbit transfer calculatorDelta-v, burn by burn, and transfer time between two circular orbits around Earth, the Moon, Mars, Jupiter or the Sun, with the target's lead angle, how often launch windows come round, and a bi-elliptic comparison. #47
• Porkchop plotDraw a porkchop plot for a trip from one planet to another: launch energy and arrival speed for every launch date and flight time, the cheapest window, and the burns from a parking orbit. #63
• Satellite ground track and passesPaste a satellite's TLE or design an orbit to see its ground track on a world map, its period, speeds and how Earth's bulge turns it, and the times it passes over your place. #66

Research 2

Coordinates, time systems and catalogue work for students and researchers.

• Astronomy time converterConvert any moment between UTC, your local time, Julian Date, Modified Julian Date and Unix time, and see sidereal time, ΔT and light-time corrected BJD for a star. #22
• Sky coordinate converterConvert a sky position, or a whole target list, between J2000, JNow, galactic and ecliptic coordinates, and see where it is in your sky right now. #23