There are a lot of asteroids in the Solar System, plenty of which are visible through small telescopes.
It’s therefore unsurprising that some will, from time to time, appear to pass across extended deep-sky objects like star clusters.
Over the coming weeks in early 2025, there'll be a chance to track a couple of these interesting events.
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Asteroid 28 Bellona
The first is to locate asteroid 28 Bellona. At the end of February 2025, this 100km object will appear relatively near the Beehive Cluster, M44, in Cancer, the Crab.
If you can locate it during February 2025, shining at mag. +10.1 against the background stars of southern Cancer, you should be able to get into the habit of keeping track of it as continues towards M44 during March.
It eventually appears to cross the cluster from the end of March into April, when it’ll be dimmer at around mag. +11.5.
As the Beehive is very easy to find mid-way between Regulus (Alpha (α) Leonis) and Castor (Alpha (α) Geminorum), locating 28 Bellona during its cluster-crossing period shouldn’t be too hard.
If you’ve never observed an asteroid passing through a star field before, this is a great place to start.
Asteroid 8 Flora
In March 2025, 8 Flora will reach opposition, when it can be seen shining at mag. +9.6 against the stars of southeast Leo.
Keeping track of Flora through March and into early April, you’ll be able to watch as it passes through the Leo Triplet, a famous patch of sky containing the three relatively bright galaxies, M65, M66 and NGC 3628.
At mag. +10.1, 8 Flora actually passes in front of NGC 3628, the Hamburger Galaxy, between 9 and 12 April.
Photographing the asteroids
Both events will make for great photo opportunities, especially if you start gathering images of each object early and compile them into an aligned composite designed to show how their individual dots track against the background stars and galaxies.
If you’re an imager, you’ll need to plan your field of view to cover the whole path of the asteroids.
Weather will affect your observations, creating gaps in the capture sequence, but that’s a reality of astronomy!
The Moon will have an influence too, brightening the sky as it passes along the section of the ecliptic closest to the asteroids.
So, what originally seemed to be a fairly simple exercise turns out to be a challenging project to keep all of the images similar enough in appearance to be combinable for the final composite.
Ultimately, a great training challenge to improve your observational and imaging skills.
Let us know how you get on and share any images you captured by emailing contactus@skyatnightmagazine.com
