Targets for April 28–May 5, 2016
Small telescope: Double stars Zeta and Iota Cancri
Large telescope: Spiral galaxy NGC 2841
Large telescope: Spiral galaxy NGC 3169
This week’s small-telescope target is pair of double stars in Cancer the Crab. The first, Tegmeni, otherwise known as Zeta (ζ) Cancri, sits 7° west-southwest of the Beehive Cluster (M44).
Tegmeni’s A star shines at magnitude 5.6, and the B component isn’t far behind at magnitude 6.0. Both glow with an attractive yellow light. The separation between the two stars is 5.9″, which means you can split this pair with a 2.4-inch telescope, but you’ll need to use a magnification of 125x or above.
The star’s name, sometimes spelled Tegmen, means “in the covering,” and may refer to its position on the rear edge of the Crab’s shell.
Our second binary, Iota (ι) Cancri, is the northernmost star in this constellation’s inverted Y shape. This pair exhibits more of a difference in brightness than Tegmeni. The magnitude 4.2 primary is nine times as bright as the magnitude 6.6 secondary.
Iota is a great target for any size scope because of the wide separation and the stars’ colors. Some 30″ lies between the two luminaries. The primary shines yellow, and its companion is blue.
It’s galaxy season
This week’s first large-telescope object is spiral galaxy NGC 2841 in the constellation Ursa Major the Great Bear. You’ll find this treat 1.8° west-southwest of magnitude 3.2 Theta (θ) Ursae Majoris.
What a gorgeous object! This magnitude 9.3 galaxy tilts southeast to northwest and displays a classic disk appearance. Its nucleus is wide and bright. NGC 2841 is also pretty big. It measures 8.1′ by 3.5′.
Through an 8-inch telescope, you’ll see several dark regions within the tightly wound spiral arms, but the arms themselves are tough to see even at high powers.
A rich galaxy field
This week’s second large-scope target is spiral galaxy NGC 3169 in Sextans the Sextant. This object will give you twice the observing pleasure. It combines magnitude 10.2 NGC 3169 with the magnitude 10.5 spiral NGC 3166, which lies only 8′ to the west-southwest.
Furthermore, the pair forms a noninteracting quartet with two more spirals — magnitude 13.9 NGC 3165 and magnitude 12.1 NGC 3156. To find it, look 4.1° north-northeast of magnitude 4.5 Alpha (α) Sextantis.
Through an 8-inch telescope, NGC 3169 appears about twice as long as it is wide, oriented northeast to southwest. Its measurements are 5.0′ by 2.8′. The central region, also elongated, is much brighter than the halo.
NGC 3166 appears ever so slightly oval (4.8′ by 2.3′), stretched in an east-west direction. Its central region is wide, and its halo is thin.
Expand your observing at Astronomy.com
The Sky this Week
Get a daily digest of celestial events coming soon to a sky near you.
Observing Basics
Find more guidance from Senior Editor Michael E. Bakich with his Observing Basics video series.
