Vernal Equinox

Spring (Vernal) Equinox is on March. 21 at 01h 00m

Comet C/2002 V1 (NEAT) - update March 3

A series of clear evenings made it possible to observe the comet from Rousay on Feb. 12 and Feb. 14. Despite a very good sky on the evening of 15th the comet was not seen - by then (17 50) it was only 9.5 arc degrees from the Sun and the twilight very strong.

Both observations on the 12th and 14th showed the comet still brightening (estimated mag. 2.0 on 12th). Seen in a red, twilight sky on the 14th the comet had all the appearance of a phantom in 20x80 binoculars.

Occultation by Jupiter of S Cancri - Mar 21

Dia 1: Jupiter showing position of S Cancri in respect to Io and Europa at Mar. 2, 01h 00. Click for an enlargement

Jupiter is still retrograding towards the open cluster M 44 (Beehive Cluster). In the early hours of March 21, Jupiter will pass in front of the star S Cancri (variable: max. mag. 8.3*).

The opportunity to see the occultation of a comparatively bright star by a planet does not occur as frequently as one might imagine; this event should be within the reach of observes using small telescopes (80mm refr. at x80). Those with larger instruments should attempt to time the disappearance as accurately as possible.

At the time of disappearance (approximately 4h 22m), Jupiter will be only 6½ degrees above the western horizon. Re-appearance occurs with the planet below the horizon from Orkney. Weather permitting, observers should commence their observations as soon as possible on the night 20/21 March*.

A field diagram for March 21 at 01 hrs is given in dia 1. The star is between Europa and Io. Europa passes into eclipse at 02 36 and re-appears approximately 6 minutes after the disappearance of S Cancri.

Jupiter is "stationary" on April 3/4, after which it resumes its forward motion towards Leo.

(* - S Cancri is an eclipsing binary (variability: magnitude 8.3 - 10.3). The precise time of maximum for this event is uncertain, therefore it is important to commence observations early in order to monitor the position, as suggested.)

Aurora and related phenomenon

I am frequently asked by newcomers to Orkney when is the best time to look for the Merry Dancers.

Obviously for any night-time observation one needs a clear sky; but a perfectly clear, moonless night cannot guarantee a display of the aurora.

Fig. 2: 2002 Aug. 16 10.42 UT. The Sun in full photographed in H-alpha (filter: Daystar ATM 0.7Å); exp. 1/125 sec on Kodak TP 2415 150mm Cooke refractor focal length 2 metres stopped to 66mm f/30.

Aurora are most likely to be seen close to times of high solar activity. Direct visual* evidence of the Sun's activity is demonstrated by the frequency, appearance, size and distribution of sunspots. But spots are not the only phenomenon associated with high solar activity. Important to the Earth are the streams of ionic particles ejected from the Sun which, on arrival in the high atmosphere of the Earth, interact to give "magnetic storms" and other manifestations, including aurora.

Fig. 2: 2002 August 16 15.10 UT. The Sun in region of large sunspot photographed in H-alpha (filter: Daystar ATM 0.7 Å0; exp. 1/60 sec on Kodak TP 2415: 150mm Cooke refractor focal length 2 metres stopped to 100mm f/62 (efl 6.2 metres).

Magnetic effects may be monitored in a number of ways. Evidence of unusually high magnetic disturbance on magnetometers at ground level is frequently associated with aurora. Space probes are better able to give us some indication of an impending "storm" but there is no guarantee that a spectacular aurora will follow. Solar activity was at its peak last year. It will peak again in approximately eleven years hence.

There have been a number of fine displays of the aurora over the past two years. (An archive is to be established on this website for the aurora, the noctilucent clouds and other phenomena of interest. Readers are invited to contribute. Please contact me at Springfield, Rousay.)

*Observing the Sun has to be conducted with great caution. Never look at the Sun with the unaided eye and certainly never through any optical device that is not specifically designed for the purpose. Those interested in looking for sunspots are best advised to use the projection method details of which may be had through this web site. But projecting or observing with ordinary dense filters will only reveal spots as dark areas against a brighter background with penumbral effects in some cases. More detailed and rewarding views can only be had by the use of special filters or instruments designed for selective wavelengths.

The most frequently used region of the spectrum is the H-alpha light of hydrogen. Seen in Halpha the Sun takes on a different aspect all together. (See Figs. 2, 3, 4). It is now possible, at some expense, to purchase binoculars equipped with filters which enable one to look at the Sun in the H-alpha with safety. (See: www.coronadofilters.com or contact the writer for further details.)

Fig 4: 2002 March 2 10.32 UT. The Sun showing large prominence. Photographed in H-alpha (filter: Daystar ATM 0.7 Å); exp. 1/60 sec on Kodak TP 2415: 150mm Cooke refractor focal length 2 metres stopped to 100mm f/52 (efl 5.2 metres). All photographs by M J Hendrie, Colchester, Essex; to whom grateful thanks are tendered.

J.V.
Feb 7, 2003