Event Date: August 18th
Time: 5:30 AM
Brief
Keep a good eye on Mercury the next two mornings, as it brightens faster and reaches dichotomy. It is approaching a star seen to its east this morning, moving towards it in prograde motion. At 1 1/2º apart is Asellus Australis (Delta Cancri): a double star within the crab's boundaries at magnitude 3.9. Since skies are dark enough now when Mercury and the star get slightly out of atmospheric pollution, we can see them easily as a pair in binoculars or in a wide-field telescope. If skies are clear enough and we wait long enough for them to get higher, we can see them both with the eye. Seeing the star this way is challenging, and especially if waiting too long and the Sun's glare gets in the way.
Image number one is the zoom-out, and the second a zoom-in with a field of 2º.
Time: 5:30 AM
Brief
Keep a good eye on Mercury the next two mornings, as it brightens faster and reaches dichotomy. It is approaching a star seen to its east this morning, moving towards it in prograde motion. At 1 1/2º apart is Asellus Australis (Delta Cancri): a double star within the crab's boundaries at magnitude 3.9. Since skies are dark enough now when Mercury and the star get slightly out of atmospheric pollution, we can see them easily as a pair in binoculars or in a wide-field telescope. If skies are clear enough and we wait long enough for them to get higher, we can see them both with the eye. Seeing the star this way is challenging, and especially if waiting too long and the Sun's glare gets in the way.
Image number one is the zoom-out, and the second a zoom-in with a field of 2º.
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| click on images to enlarge: courtesy of Starry Night Pro Plus, version 6.4.3, by Simulation Curriculum Corp. |
Tomorrow when I revisit this pair, they will be quite a sight with a high magnification: Mercury will be just past dichotomy, just starting a waxing gibbous phase, and the star will be very close to it. Not often do we see Mercury so close to an unaided-eye magnitude star, and especially when Mercury is at such a good magnitude (-0.3 this morning and a little better than -0.4 tomorrow). With the geometry of the eastern morning sky improving fast between now and early October, it remains good throughout early December when we have our final Mercury morning apparition of the year. Between now and then, we have a poor evening apparition of Mercury, which will make it hard to see it near stars; it will be south of the Sun for that one, while north of the Sun right now for this one. Be ready for tomorrow and have a telescope with a low-focal length eyepiece ready! Even using a telescope with a long-focal length eyepiece and/or low f-ratio telescope, you can notice a deep sky attraction near the pair; I will reveal that tomorrow as well.
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