Comets

103 P/Hartley 2 2010-10-07.
This periodic comet comes closest to the Sun just outside the Earth's orbit. The 2010 perihelion occurs just as the Earth itself is on that side of the Sun, both helping the apparent brightness of the comet and allowing it to be seen all night. In this image the comet is approaching the open star clusters χ and h Persei. The picture on the left is made from 8 frames taken over a period of somewhat over one hour with the frames aligned on the stars. The comet makes a trail due to its movement during that period. On the right the same frames are aligned on the comet, turning all stars into trails.
Edinburgh. f = 135 mm, f/4, 5 min per frame. Canon EOS 300D. Stack of 8 frames.

Comet C/2007 N3 Lulin 2009-03-01.
In February 2009, comet Lulin passes both opposition and closest to the Earth. It passes through the constellation of Leo past Saturn and later Regulus.
Edinburgh. f = 135 mm, f/2.8, 1 min per frame. Canon EOS 400D. Stack of 16 frames.

Comet 17P/Holmes 2007-11-11.
In late October 2007, comet Holmes brightens about 500,000-fold from being beyond the reach of amateur astronomers' telescopes to competing with the brighter stars of the night sky - easily visible to the naked eye. From day to day its coma grows, while its total brightness remains more or less constant. Here it is almost the apparent size of the Sun.
Edinburgh. f = 400 mm, f/6.3, 2 min per frame. Canon EOS 400D. Stack of 4 frames.

Comet C/2004 Q2 Machholz 2005-01-29.
At the end of January 2005, comet Machholz passes the double cluster of χ and h Persei, which is caught just in the bottom right corner. The blue ion tail can be seen emerging to the left from the head (the coma). A second tail points to the bottom left, apparently caused by dust that is lagging behind the comet in its orbit.
Earlyburn. f = 135 mm, f/2.8, 10 min, 400 ISO. Canon EOS 300D.

Comet C/1995 O1 Hale-Bopp 1997-03-28.
The comet has passed through the constellation Cassiopeia (top of the image). Both the blue straight ion tail and the curved white dust tail are visible and about 10° long. The original image is affected by sodium-illuminated cloud at the bottom right and by a general background gradient. Removal of this has not been quite perfect, and did nothing about the scanner artefact that is a blue horizontal bar near the centre.
East Lothian. f = 50 mm, f/1.8, 165 s, 100 ISO. Praktica VLC2, Fujichrome. Spline background subtracted.

153 P/Ikeya-Zhang 2002-03 and 2002-04.
Montage of seven images of this bright comet of spring 2002. All are adjusted to the same brightness representation, all are adjusted to the same scale (~106 pix/° in the full version), and all are rotated to be oriented in equatorial coordinates. Observe how the direction of the tail changes as the comet moves across the sky from the evening West horizon to high declination low above the North horizon, the tail always pointing away from the Sun. Also observe how the balance between the broad, bent dust tail and the thin, straight ion tail changes over time.
The images were taken (left to right) on the evenings of 2002-03-13, 2002-03-25, 2002-03-29, 2002-04-01, 2002-04-06, 2002-04-07, 2002-04-16. Black corresponds to a surface brightness of -1 MJy/sr, pink to +5 MJy/sr, and white to 50 MJy/sr.
Earlyburn. f = 50 mm, f/1.8 (f/2.2 for third image). First image Philips ToUcam Pro, the rest Logitech QuickCam VC. Third and fourth stationary on tripod, the others piggyback on Celestron 8. Exposure times 10 to 20 min. Combined grey and false colour encoding of brightness.