Jump to content


Photo

Stellar object interval?

  • Please log in to reply
4 replies to this topic

#1 jrbuete

jrbuete

    Explorer 1

  • -----
  • Posts: 53
  • Joined: 10 Feb 2013
  • Loc: SoCal

Posted 26 April 2013 - 11:02 AM

Once an item, say M42 sets in the west at sunset, how long until is rises in the east at sunset? Curious because I was just getting into some serious viewing of M42 and now it's below my horizon (trees and mountains) :confused:
I think I know but wanna be sure:)

#2 ThreeD

ThreeD

    Apollo

  • -----
  • Posts: 1029
  • Joined: 23 Dec 2008
  • Loc: Sacramento suburbs

Posted 26 April 2013 - 12:53 PM

In 6 months it will be at located 180 degrees away from its current position with respect to Polaris assuming the same time of day (UTC -- so not including DST).

If you actually want to view it near sunset then you need to realize that you need to wait a few months longer to allow it to rise sufficiently above the horizon. If you want to view it sooner, then wait a few months from now and you can catch it in the morning before sunrise.

--Scott

#3 Tony Flanders

Tony Flanders

    Voyager 1

  • *****
  • Posts: 11173
  • Joined: 18 May 2006
  • Loc: Cambridge, MA, USA

Posted 26 April 2013 - 01:05 PM

Once an item, say M42 sets in the west at sunset, how long until is rises in the east at sunset?


It depends on the object's declination and on the season. And also, of course, what you mean by "at sunset." No deep-sky object is visible less than 45 minutes after sunset, especially if it's low in the sky.

M42 is a smidge south of the celestial equator, so at northern latitudes it spends almost half of the time above the horizon. That means it will be reappearing at roughly the same time of night in roughly 6 months. As luck would have it, nights will be significantly longer by then, so it will indeed be visible not long after sunset despite the 1.5 to 2 hours lost to twilight.

Far-north objects like M81 and M82 are always above the horizon for observers around latitude 40 north, and therefore observable whenever the sky is reasonably dark.

Far-south objects like M7 just skim above the horizon for a few hours, so their viewing season is quite short.

#4 bherv

bherv

    Surveyor 1

  • *****
  • Posts: 1610
  • Joined: 10 Mar 2006
  • Loc: WMass

Posted 26 April 2013 - 05:58 PM

If you stay up late or get up in the predawn hours, Orion returns to dark sky by late summer. By mid-September it is high enough before dawn to get decent views of M42. As far as the evening goes, you have to wait until November before it gets high enough at a decent hour. Most of my viewing of Orion comes in the fall during the wee hours of the morning.
Barry

#5 jrbuete

jrbuete

    Explorer 1

  • -----
  • Posts: 53
  • Joined: 10 Feb 2013
  • Loc: SoCal

Posted 26 April 2013 - 08:01 PM

Thanks, pretty much what I thought based on its RA/DEC... have to put that target on hold for a while...






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics