This month’s highlights include the Little Crab, a former 16th-century constellation
1. The Little Crab
Recommended equipment: 10×50
The 48 Greek constellations had gaps between them, and some of these were filled with new constellations. For a few decades in the 16th century, Cancer Minor, proposed by Flemish astronomer Petrus Plancius, was one of these. This asterism of different coloured 5th magnitude stars extends 7° from 85 Geminorum to 68 Geminorum, looking like a fainter version of Sagitta. It’s 6° south of Kappa (κ) Geminorum.
2. Mekbuda
Recommended equipment: 10×50
Mekbuda (Zeta (ζ) Geminorum) is a Cepheid variable (mag. +3.6 to +4.2) star. The period of a Cepheid is proportional to its luminosity (intrinsic brightness) so, merely by measuring its period, you can determine its distance by comparing its luminosity with magnitude. Mekbuda’s period is 10.15 days, so you can obtain a light curve in a month. It is an easy, wide double star.
3. VZ Cancri
Recommended equipment: 10×50
If 10.15 days is too long for you and you want to watch a star complete its cycle of variability in a single session, this is the one for you! VZ Cancri oscillates between mag. +7.2 and +7.9 over a period of 4 hours 17 minutes. You’ll find it midway between 49 and 36 Cancri. VZ is a RR Lyrae variable; it has a rapid rise in brightness followed by a dimming.
4. RV Monocerotis
Recommended equipment: 10×50
RV Monocerotis is an altogether different experience. This red giant star takes 121.3 days to cycle through magnitudes +6.9 and +7.7. It is classified as a semi-regular variable owing to its underlying periods of 91.8 and 1047 days. There are no bright markers nearby, so find it by taking a line from Alhena (Gamma (γ) Geminorum) through Xi (ξ) Geminorum and extending it a further 7.5° – RV is the reddest star in the field of view.
5. M50
Recommended equipment: 10×50
M50 lies 8° from Delta (δ) Monocerotis in the direction of Theta (θ) Canis Majoris. Expect to see a circular glow about half the Moon’s apparent diameter. This comes from just over 100 stars, but you won’t be able to resolve more than four or five, depending on the sky’s darkness, in 10×50 binoculars.
6. Pakan’s 3
Recommended equipment: 15×70
This little asterism is 3° southwest of M50 and 2° north of Theta (θ) Canis Majoris. As long as you have a dark transparent sky, the number ‘3’, which is composed from 11 (9th magnitude) stars, stands out from the background Milky Way. Spend a bit of time on it with mounted binoculars, when the colours of the stars, ranging from white to orange, become more perceptible.
Photo: PETE LAWRENCE