Cool Sun Facts · Comet hunting practice
Practise hunting comets in the Sun's glare
In the Sungrazer Project, volunteers search spacecraft images for comets passing close to the Sun. NASA says over half of all known comets were first discovered by its contributors, and that no prior knowledge is needed. Here you can practise the method on real images of a comet whose story is long settled.
How the project tells a comet from everything else
- A comet moves in a near-perfect straight line at a near-constant speed, and keeps its size, shape and brightness, across at least five consecutive images.
- Cosmic-ray hits, specks and streaks made by energetic particles, appear once, anywhere.
- Stars always move from left to right, horizontally, all at the same speed; planets move horizontally too, are bigger and brighter, and carry spikes.
- Before reporting, hunters measure the object's position in each image: speeds between images that differ by more than 10 pixels an hour (in the C3 camera) mean it is not one moving object.
Practice: five frames from SOHO's widest camera
Two real sequences, each with a documented answer. Find something that moves steadily from frame to frame and mark the same point on it in each: click or tap the image, or type its position (0 to 1024 across and down). Not every sequence has a comet in it.
| Frame | Time (UTC) | Mark (of 1024) |
|---|
Images: SOHO/LASCO C3, from the SOHO archive (15 December 2011; 20 January 2005), loaded as you step through them. Courtesy of SOHO/LASCO consortium. SOHO is a project of international cooperation between ESA and NASA (credit as SOHO asks).
What these frames show
- The bright moving object with a tail is Comet Lovejoy, C/2011 W3, a Kreutz sungrazer announced on 2 December 2011. It entered this camera's view early on 14 December and skimmed about 140,000 km above the Sun's surface late on 15 December and early on 16 December.
- It passed closest to the Sun at 00:17 UTC on 16 December and, against expectations, survived: the first Kreutz comet to do so in the space age.
- The dark band reaching to the centre is the support for the occulter disk, part of the camera, and the white circle marks where the Sun's disc is, hidden behind it. Neither is in the sky.
- The fixed points of light are background stars, which the guide says drift from left to right, all together and slowly; a speck in only one frame is a cosmic-ray hit.
- This comet was found and confirmed long ago. Marking it is practice, not a discovery.
What these frames show
- No comet. A solar flare began just before 2 a.m. Eastern time on 20 January 2005 (about 07:00 UTC), and a storm of energetic protons reached Earth about 15 minutes later.
- The protons strike the camera's detector, and NASA describes the result as snow in the images: the frames after 07:00 are covered in specks and short streaks that were never in the sky.
- The project's guide says such hits appear once, anywhere, so a speck you mark in one frame will not line up with anything in the next, and the marks fail the speed rule. The dark band and the white circle are, as before, the occulter's support and the Sun's position.
- A storm like this is why hunters check that an object keeps a steady line over at least five frames before reporting it.
Taking part for real
The project's official guide to SOHO comet hunting explains the whole method, including how to check what has already been reported. New finds are reported only on the project's own reporting page, under its rules. This site sends nothing to the project and reports nothing for you; a practice note saved here stays in this browser.
Sources
- NASA The Sungrazer Project (opens in a new tab) for volunteers find sungrazing comets in SOHO and STEREO images; over half of all known comets first found by contributors; no prior knowledge needed · checked 2 October 2026
- US Naval Research Laboratory, Sungrazer Project The "Official Guide" to SOHO Comet Hunting (opens in a new tab) for comets move in a near-straight line at near-constant speed in at least five consecutive images; cosmic rays appear once; stars move left to right horizontally; planets horizontally with spikes; speeds differing by more than 10 px/h in C3 (60 in C2) mean a false report · checked 2 October 2026
- ESA & NASA, SOHO LASCO C3 browse images, 15 December 2011 (opens in a new tab) for the dated frames shown in the first practice · checked 2 October 2026
- ESA & NASA, SOHO LASCO C3 browse images, 20 January 2005 (opens in a new tab) for the dated frames shown in the second practice · checked 2 October 2026
- ESA & NASA, SOHO SOHO copyright and credit (opens in a new tab) for public education use encouraged without authorization; credit "Courtesy of SOHO/LASCO consortium. SOHO is a project of international cooperation between ESA and NASA." · checked 2 October 2026
- ESA & NASA, SOHO The Great "Birthday Comet" of 2011 (Pick of the Week, updated 16 December 2011) (opens in a new tab) for Kreutz comet C/2011 W3 (Lovejoy), announced 2 December 2011; entered LASCO C3 early on 14 December; skimmed about 140,000 km above the surface late 15 to early 16 December; unexpectedly survived · checked 2 October 2026
- NASA Solar Dynamics Observatory Comet Lovejoy Event (opens in a new tab) for perihelion at 00:17 UTC on 16 December 2011; the first Kreutz comet to survive perihelion in the space age · checked 2 October 2026
- ESA/NASA SOHO About the SOHO real-time images (opens in a new tab) for LASCO C2 shows the corona to 8.4 million km; C3 spans 32 solar diameters; the white circle is the Sun's disc; streamers; occasional CMEs · checked 2 October 2026
- NASA Scientific Visualization Studio SOHO/LASCO View of January 2005 Solar Events (opens in a new tab) for the 20 January 2005 flare began just before 2 a.m. ET; a storm of energetic protons reached Earth 15 minutes later; the storm causes 'snow' in the LASCO images as radiation swamps the cameras · checked 2 October 2026
- US Naval Research Laboratory, Sungrazer Project Report a comet (opens in a new tab) for the project's own reporting page · checked 2 October 2026