This has been, on paper at least, one of the best weeks ever to try astrophotography. The global lockdown means much less pollution in the atmosphere, giving a clearer view of the stars.... and then there is the added bonus of no airplanes in the sky adding unwanted lines to our long exposures.
In the fourth of our five-part guide to spring astrophotography we are going to going to shoot 'planetshine' using a double exposure technique.
Everyone photographs the full Moon, but for a more delicate sight try searching for a crescent Moon. For most of this week the Moon is invisible, since its New Moon on Thursday, 23 April, but for a couple of mornings beforehand, and a few evenings afterward, there will be a super-slim crescent Moon ‘chasing’ the Sun’s set and rise. The photographic prize here is ‘planetshine’ or ‘earthshine’ on the Moon’s dark portion.
Look at the slither of the lit-up part of the Moon, then cast your eyes to the darker, un-lit part of the Moon, and you’ll notice that you’re able to see some detail on the Moon’s surface. That's because some sunlight is being reflected from Earth and on to the Moon. It's always happening, but while human eyes have the dynamic range to see it (when the moon is very slim), cameras do not.
To capture ‘planetshine’ in a close-up you need to expose separately for the ‘sunshine’ side (ISO 400, 1/800 sec. to prevent over-exposing) and ‘planetshine’ side (ISO 800, 2 seconds to get some detail but avoid blurring) using a long lens.
- Thursday, April 23: ‘sighting’ of a 1% crescent moon signals the start of the Islamic festival of Ramadan (though you need a very low view to the western horizon)
- Friday, April 24: moonset occurs over an hour after sunset
- Saturday, April 25: the crescent moon is between the Pleiades and Hyades
- Sunday, April 26: the crescent moon will be close to bright planet Venus
Experiment with different ISO and exposure times (particularly for the ‘planetshine’ side) and you’ll end up with two images to combine using a layer mask in Photoshop. If you use a wide-angle lens then one judicious exposure is usually enough to show the phenomenon.
However, be prepared to experiment because the light is tenuous and rapidly changing in the blue hours. Here’s when to try shooting ‘earthshine’ this week (get moonset times for your location).