Comet Holmes
The comet that brightened nearly a million times in a day in 2007, briefly becoming bigger than the Sun.
Key facts
- Designation
- 17P/Holmes
- Type
- Jupiter-family comet
- Orbital period
- about 6.9 years
- Closest to the Sun
- about 2.1 AU (about 310 million km)
- Farthest from the Sun
- about 5.2 AU
- Tilt of orbit
- about 19°
- Nucleus
- about 3.4 km across
- Discovered
- by Edwin Holmes in London on 6 November 1892, during an outburst
- Returns
- at perihelion in 2021; next in 2028
Orbit
Holmes goes round the Sun every seven years, staying beyond Mars's orbit. It never comes near Earth and is normally faint.
Size and nature
The nucleus is about 3.4 km across. On 23 and 24 October 2007 it erupted, brightening from about magnitude 17, visible only in large telescopes, to about magnitude 2.8, plain to the naked eye, in less than two days. That is a rise of nearly a million times. The cloud of dust and gas expanded until, in November, it was wider than the Sun, briefly the largest object in the Solar System, though it held only a tiny amount of material. Watchers in Britain saw a fuzzy yellow star in Perseus that grew night by night.
History
Edwin Holmes, an English amateur astronomer, found it in 1892 during a similar outburst, and it flared again weeks later. Then it faded and was lost for decades. The cause of such outbursts is not settled; one idea is that a pocket of gas under the crust bursts through, or a part of the surface collapses.
Meteor showers
Its orbit does not reach Earth, so it has no meteor shower.
Key dates
| Date | What happened |
|---|---|
| 6 November 1892 | Edwin Holmes discovered Comet Holmes during an outburst. |
| 24 October 2007 | Comet Holmes brightened nearly a million times, becoming visible to the naked eye. |
Did you know?
It is the largest outburst ever recorded for a comet.
The dust cloud in November 2007 was wider than the Sun.
Both its discovery and its 2007 eruption came in the autumn, from Perseus.