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seen Aug 17 at 9:12

Astrophysicist, Linux fan.


Aug
17
answered Is it possible for a person to not see the new moon at different places on earth?
Aug
15
comment What is star composition after formation
I think there may be confusion here between "a gas cloud reaches a critical mass/radius and collapses to form a star" and "the protostellar core reaches a critical temperatre and starts hydrogen fusion". See e.g. en.wikipedia.org/wiki/Jeans_instability for the former.
May
30
answered How to determine period of pulsar?
Jan
6
answered How to calculate Longitude from Right Ascension?
Jan
6
answered How to calculate the altitude of the Moon?
Nov
23
comment Can I see comet ISON from Saudi Arabia?
I added the code to libTheSky. This link points to github and my contact data in case you have questions. Check the functions best_planet_xsmag() and pl_xsmag() in the file visibility.f90 (it's in Fortran, sorry ;-)).
Nov
23
comment Can I see comet ISON from Saudi Arabia?
I use elements and magnitude data from the MPC - not perfect, especially for "first-time" comets. Still, the best moment for observation may suffer relatively little from systematic effects.
Nov
21
comment Can I see comet ISON from Saudi Arabia?
I apologise for the loss of format above (paste it into your text editor to restore the three columns). Summarised, the table indicates you could see ISON with the naked eye on Nov 17-21 and Dec 11-25, best around Dec 17 at 5:15 AST. The computer code is very simple and while I think that the best dates and times are roughly correct, the magnitudes are probably not and you may well need binoculars to see ISON as the original answer indicates.
Nov
21
comment Can I see comet ISON from Saudi Arabia?
Good, and I was wrong. I wrote a small program to compute exactly that: the "excess magnitude" defined as <limiting magnitude> - <comet magnitude corrected for airmass>, where positive values indicate you may see the object with the naked eye. I get (for Riyadh): Nov: Day time Exc.mag 15 4:56 -0.2 17 4:59 0.1 19 5:03 0.3 21 5:08 0.2 23 5:17 -0.4 25 5:53 -1.3 27 6:10 -2.2 (28 17:06 -50.7 - never visible) Dec: 01 6:15 -3.4 03 6:04 -2.3 05 5:57 -1.8 07 5:29 -1.3 09 5:23 -0.4 11 5:21 0.1 13 5:18 0.3 15 5:17 0.3 17 5:15 0.4 19 5:16 0.3 21 5:15 0.3 23 5:16 0.2 25 5:13 0.1 27 5:14 -0.0
Nov
21
comment Can I see comet ISON from Saudi Arabia?
I think the term "most visible" is somewhat vague. Early (~5th of) December may be more favourable than later in the month, even though you'll have to observe it in twilight. As the days go by, you can indeed see the comet earlier, against a darker sky background and higher above the horizon, but the object itself will also be dimmer. You may therefore always need binoculars to see "ISON".
Nov
17
comment How do scientists determine the age of stars?
Also, what do you mean with 'oldest galaxies'? We see the galaxies that are farthest away from us while they are still very young, since their light took about the age of the universe to reach us. In contrast, we see nearby galaxies while they're old, since their light only took a few million years to get here. Yet, both are about equally old (formed at roughly the same time after the Big Bang).
Nov
17
comment How do scientists determine the age of stars?
I think you're confusing at least two things - the age of a star, and the time it took its light to arrive on Earth. The first tells how long ago a star was formed, the latter how far away it is.
Oct
27
answered How can I observe the Orionid Meteor Shower?
Oct
20
awarded  Teacher
Oct
20
answered How does moonrise/moonset azimuth vary with time?
Oct
20
answered Why don't Neutron Stars form event horizon?